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Nestlings of altricial birds are not typically provisioned water. For the first time in a wild altricial bird we provide annotated video documentation of adult pied crows (Corvus albus) gathering water with their bills and provisioning it to their nestlings in a similar manner as food is delivered. The circumstances of this provisioning suggest that the function is to dislodge anthropogenic food (mainly boiled rice, which has a sticky consistency) from the parent's bill, flush it into the mouth of the nestling, and facilitate swallowing. The means by which the adults gather the water without swallowing and transport it is also unusual. Water provisioning by pied crows is a previously undescribed example of corvid ingenuity, likely in an effort to handle novel food in a human-altered environment. [ABSTRACT FROM AUTHOR]

The mammalian skull base ossifies from chondral elements into successive bones described as the basicranial stem or axis. The axis includes the basioccipital, basisphenoid, presphenoid, and mesethmoid bones. Accurately tracing the ontogenetic origin of this area is essential, as endochondral development plays a crucial role in understanding the homology of these axial bones. This area contributes to building the ethmo-sphenoidal area and contains phylogenetic signal. In our study, we examined the ontogeny of the neurocranial base and allied bones (i.e., alisphenoid and orbitosphenoid) in representatives of two living armadillo clades: Dasypus hybridus (n = 18) (Dasypodidae), Chaetophractus vellerosus (n = 9) and Chaetophractus villosus (n = 11) (Chlamyphoridae). The presphenoid is not ossified in D. hybridus, C. villosus, or C. vellerosus; moreover, there is no clear evidence that this bone forms a separate ossification in other cingulates. In addition, there is evidence for the existence of postnatal mesethmoid ossification in armadillos. There are different ontogenetic trajectories in armadillos, precocial for Dasypus and altricial for Chaetophractus. The presence of the mesethmoid is likely a plesiomorphic condition for Placentalia. [ABSTRACT FROM AUTHOR]

Simple Summary: Mammals nurse their young through rapid early growth. Most placental mammals bridge the period with a set of small, temporary 'deciduous' or 'milk' teeth. At some point, a mother weans her young, who must then feed independently to survive. How tooth eruption integrates with gestation, birth and weaning is explored here for 71 species in nine mammalian orders. Body weights range from 22 g to 4300 kg and maternal investment (gestation plus nursing) ranges from 6 weeks to more than 7 years. These mammals differ widely at birth, from no teeth to all deciduous teeth emerging, but commonalities appear when infants transit to independent feeding. Weaning takes place with an entire deciduous dentition, closest in time to emergence of the first permanent molars and well before second molars emerge. Adult body size explains less about tooth eruption than expected. Instead, many mammals, from monkey to moose, limit maternal investment (from initial pregnancy to young with first molars) to just under one year, timing infant development to annual cycles. Mammals that invest multiple years in their young include several critically endangered species. Integrating tooth emergence into life history gives insight into living mammals and builds a framework for interpreting the fossil record. The young of toothed mammals must have teeth to reach feeding independence. How tooth eruption integrates with gestation, birth and weaning is examined in a life-history perspective for 71 species of placental mammals. Questions developed from high-quality primate data are then addressed in the total sample. Rather than correlation, comparisons focus on equivalence, sequence, the relation to absolutes (six months, one year), the distribution of error and adaptive extremes. These mammals differ widely at birth, from no teeth to all deciduous teeth emerging, but commonalities appear when infants transit to independent feeding. Weaning follows completion of the deciduous dentition, closest in time to emergence of the first permanent molars and well before second molars emerge. Another layer of meaning appears when developmental age is counted from conception because the total time to produce young feeding independently comes up against seasonal boundaries that are costly to cross for reproductive fitness. Mammals of a vast range of sizes and taxa, from squirrel monkey to moose, hold conception-to-first molars in just under one year. Integrating tooth emergence into life history gives insight into living mammals and builds a framework for interpreting the fossil record. [ABSTRACT FROM AUTHOR]

Background: Neocortex development has been extensively studied in altricial rodents such as mouse and rat. Identification of alternative animal models along the "altricial-precocial" spectrum in order to better model and understand neocortex development is warranted. The Greater cane rat (GCR, Thyronomys swinderianus) is an indigenous precocial African rodent. Although basic aspects of brain development in the GCR have been documented, detailed information on neocortex development including the occurrence and abundance of the distinct types of neural progenitor cells (NPCs) in the GCR are lacking. Methods: GCR embryos and fetuses were obtained from timed pregnant dams between gestation days 50–140 and their neocortex was analyzed by immunofluorescence staining using characteristic marker proteins for NPCs, neurons and glia cells. Data were compared with existing data on closely related precocial and altricial species, i.e. guinea pig and dwarf rabbit. Results: The primary sequence of neuro- and gliogenesis, and neuronal maturation is preserved in the prenatal GCR neocortex. We show that the GCR exhibits a relatively long period of cortical neurogenesis of 70 days. The subventricular zone becomes the major NPC pool during mid-end stages of neurogenesis with Pax6 + NPCs constituting the major basal progenitor subtype in the GCR neocortex. Whereas dendrite formation in the GCR cortical plate appears to initiate immediately after the onset of neurogenesis, major aspects of axon formation and maturation, and astrogenesis do not begin until mid-neurogenesis. Similar to the guinea pig, the GCR neocortex exhibits a high maturation status, containing neurons with well-developed dendrites and myelinated axons and astrocytes at birth, thus providing further evidence for the notion that a great proportion of neocortex growth and maturation in precocial mammals occurs before birth. Conclusions: Together, this work has deepened our understanding of neocortex development of the GCR, of the timing and the cellular differences that regulate brain growth and development within the altricial–precocial spectrum and its suitability as a research model for neurodevelopmental studies. The timelines of brain development provided by this study may serve as empirical reference data and foundation in future studies in order to model and better understand neurodevelopment and associated alterations. [ABSTRACT FROM AUTHOR]

Simple Summary: Brown adipose tissue (BAT) is a thermogenic tissue that greatly contributes to preventing neonatal hypothermia by activating biochemical and endocrine processes because of cold stress. The presence of uncoupling proteins and adrenergic receptors in the brown adipocyte initiates the metabolic pathway for heat production. However, the presence and absence of BAT, as well as its activation, location, and the degree of thermogenic response, are traits that depend on intrinsic and extrinsic factors of mammals. The present review aims to discuss the neuromodulation mechanisms of thermoregulation and the importance of BAT, emphasizing the analysis of the biochemical, physiological, and genetic factors that determine the distribution, amount, and efficiency of this energy resource in newborns of different species. Hypothermia is one of the most common causes of mortality in neonates, and it could be developed after birth because the uterus temperature is more elevated than the extrauterine temperature. Neonates use diverse mechanisms to thermoregulate, such as shivering and non-shivering thermogenesis. These strategies can be more efficient in some species, but not in others, i.e., altricials, which have the greatest difficulty with achieving thermoneutrality. In addition, there are anatomical and neurological differences in mammals, which may present different distributions and amounts of brown fat. This article aims to discuss the neuromodulation mechanisms of thermoregulation and the importance of brown fat in the thermogenesis of newborn mammals, emphasizing the analysis of the biochemical, physiological, and genetic factors that determine the distribution, amount, and efficiency of this energy resource in newborns of different species. It has been concluded that is vital to understand and minimize hypothermia causes in newborns, which is one of the main causes of mortality in neonates. This would be beneficial for both animals and producers. [ABSTRACT FROM AUTHOR]

Most vertebrates are precocial in locomotion, able to walk and run soon after birth. Precociality requires a bony skeleton of sufficient strength to resist mechanical loading during early locomotor efforts. The aim of this study was to use an animal model—the preterm infant pig—to investigate some of the proximate factors that might determine variation in bone strength in precocial animals. Based on the prior literature, we tested the null predictions that skeletal integrity would be significantly compromised by truncated gestation (i.e., preterm birth) and reduced body mass at birth. We generated a suite of both morphometric measures (tissue mineral density and cross‐sectional geometry) and performance‐related metrics (ability to resist loading, deformation, and fracture during three‐point bending tests) of the appendicular skeleton of preterm and full‐term infant pigs. Results showed that very few measures in our ontogenetic infant pig sample significantly varied with either gestation length or birth mass. Overall, our results contribute to a growing body of literature demonstrating the early functional capacity of the precocial infant musculoskeletal system and suggest that bone strength in perinatal precocial mammals may be robust to the factors shown to compromise skeletal integrity in more altricial taxa. [ABSTRACT FROM AUTHOR]

Environmental challenges faced early in life can both activate and shape the development of the hypothalamic-pituitary-adrenal axis. Activation of this axis is characterized in part by elevated levels of glucocorticoids, exposure to which can have profound effects throughout an animal's life. We have demonstrated that in nestling eastern bluebirds (Sialia sialis), bouts of environmentally relevant cooling result in elevations of corticosterone (the primary avian glucocorticoid) very early in life. Nestlings repeatedly exposed to cooling also exhibit dampened corticosterone secretion later in life in response to restraint compared to control nestlings. We explored the mechanistic basis of this phenomenon. Specifically, we asked whether early-life cooling alters adrenal sensitivity to adrenocorticotropic hormone (ACTH), the primary controller of corticosterone synthesis and release. To this end, we subjected nestlings to repeated bouts of cooling (cooled nestlings) or brooding temperatures (control nestlings) early in life and, before fledging, assessed (1) the capacity of the nestlings' adrenals to produce corticosterone following ACTH injection, (2) the effect of cooling on corticosterone responses to restraint, and (3) the effect of cooling on adrenal sensitivity to ACTH. We found that both cooled and control nestlings secreted substantially higher levels of corticosterone following ACTH treatment than they did following restraint. We also confirmed that cooled nestlings had reduced corticosterone secretion in response to restraint compared to control nestlings; however, sensitivity to exogenous ACTH did not differ between temperature treatments. We hypothesize that early-life cooling alters later corticosterone secretion by affecting higher levels of the hypothalamic-pituitary-adrenal axis. [ABSTRACT FROM AUTHOR]

The quail (Coturnix coturnix, Linnaeus 1758), a notable model used in developmental biology, is a precocial bird species in which the processes of retinal cell differentiation and retinal histogenesis have been poorly studied. The purpose of the present research is to examine the retinogenesis in this bird species immunohistochemically and compare the results with those from previous studies in precocial and altricial birds. We found that the first PCNA-negative nuclei are detected at Stage (St) 21 in the vitreal region of the neuroblastic layer, coinciding topographically with the first αTubAc-/Tuj1-/Isl1-immunoreactive differentiating ganglion cells. At St28, the first Prox1-immunoreactive nuclei can be distinguished in the vitreal side of the neuroblastic layer (NbL), but also the first visinin-immunoreactive photoreceptors in the scleral surface. The inner plexiform layer (IPL) emerges at St32, and the outer plexiform layer (OPL) becomes visible at St35—the stage in which the first GS-immunoreactive Müller cells are distinguishable. Newly hatched animals show a well-developed stratified retina in which the PCNA-and pHisH3-immunoreactivies are absent. Therefore, retinal cell differentiation in the quail progresses in the stereotyped order conserved among vertebrates, in which ganglion cells initially appear and are followed by amacrine cells, horizontal cells, and photoreceptors. Müller glia are one of the last cell types to be born. Plexiform layers emerge following a vitreal-to-scleral gradient. Finally, our results suggest that there are no significant differences in the timing of different events involved in retinal maturation between the quail and the chicken, but the same events are delayed in an altricial bird species. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nutritional nitrogen conservation is important during insect development. • Maturing Cryptocercus punctulatus cockroaches invest more nitrogen into their exoskeletons. • Neotermes jouteli termites remain small with less nitrogen investment in their exoskeleton. • Significant cuticular/exoskeleton nitrogen is lost during each successive molt. The role of nitrogen during insect development and reproduction is key in the success of a species, and is of primary importance in wood feeding taxa. Based on comparison of xylophagous, one-piece termites to the termite sister group, subsocial wood-feeding cockroaches in the genus Cryptocercus , it has been proposed that the evolution of termite eusociality involved a fundamental shift in nitrogen allocation strategies. Cryptocercus exhibits a nitrogen storage economy, with individuals gradually increasing in size and cuticular density over a years-long developmental period. Termites, however, remain in a juvenilized morphotype with minimal investment into cuticle, suggesting that nitrogen is conserved and circulated according to the needs of the colony via behaviors such as trophallaxis and cannibalism. We examined the nitrogen economy of Cryptocercus punctulatus and the dampwood termite Neotermes jouteli , focusing on cuticular nitrogen investment during development and exuvial nitrogen losses resulting from molting. Cryptocercus progressively changes from a pale, thin, soft cuticle at hatch to a dark, thick, heavily sclerotized cuticle in adults; increases in N/mg cuticle and the quantity of cuticular catecholamines are correlated with these ontogenetic color changes. There were significant differences in the nitrogen content of two successive age classes of early stage juveniles and in their discarded exuvia at molt. Soldier and alate castes of N. jouteli exhibited the highest sclerotization/melanization indices; pseudergates had levels comparable to those measured in Class I (3rd and 4th instar) juveniles of C. punctulatus. Exuvia of N. jouteli contained 0.19 μgN/mg, while exuvia of approximately two- and three-year-old C. punctulatus had 72.9 and 82.6 μgN/mg, respectively. Our data support the hypothesis that the evolution of termite eusociality from subsocial cockroach ancestors was rooted in chronic fitness limitations imposed by their low nitrogen diet. [ABSTRACT FROM AUTHOR]

Social networks are considered to be 'highly modular' when individuals within one module are more connected to each other than they are to individuals in other modules. It is currently unclear how highly modular social networks influence the persistence of contagious pathogens that generate lifelong immunity in their hosts when between‐group interactions are age dependent. This trait occurs in social species with communal nurseries, where juveniles are reared together for a substantial period in burrows or similar forms of containment and are thus in isolation from contact with individuals in other social groups.Our main objective was to determine whether, and to what extent, such age‐dependent patterns of between‐group interactions consistently increased the fade‐out probability of contagious pathogens that generate lifelong immunity in their hosts. We hypothesised that in populations of species where juveniles are raised in communal nurseries, a high proportion of recovered adults in a group would form a 'protective barrier' around susceptible juveniles against pathogen transmission, thereby increasing the probability of epidemic fade‐out in the population.To test this idea, we implemented a spatially implicit individual‐based susceptible–infected–recovered (SIR) model for a large range of generic host and pathogen traits.Our results indicated that (a) the probability of epidemic fade‐out was consistently higher in populations with communal nurseries, especially for highly contagious pathogens (high basic reproduction number, R0) and (b) communal nurseries can counteract the cost of group living in terms of infection risk to a greater extent than variation in other traits.We discuss our findings in relation to herd immunity and outline the importance of considering the network structure of a given host population before implementing management measures such as vaccinations, since interventions focused on individuals with high between‐group contact should be particularly effective for controlling pathogen spread in hosts with communal nurseries. [ABSTRACT FROM AUTHOR]

In altricial birds, leaving the nest is a key life history transition associated with a high risk of mortality. Studies of numerous species have shown that young typically fledge early in the day, and it is often asserted that early fledging is important for survival; however, evidence for this hypothesis is limited. We used an automated monitoring system to obtain precise fledging times of 1582 young blue tits, Cyanistes caeruleus , from 230 nests. As expected, nestlings primarily fledged early in the day (84% fledged before midday). However, we found no evidence that early fledging was associated with higher postfledging survival (i.e. recorded the following autumn or later). We propose two alternative explanations for the morning peak in fledging. Hypothesis 1 is that some offspring reach a developmental threshold for fledging overnight and leave the nest early the next day. This is supported by our observation that offspring that fledged early in the day tended to be more developed than those that fledged later in the day, that is, they were older and had a high body mass (measured at 14 days of age) for their fledging age. Hypothesis 2 is that the timing of fledging is related to parental provisioning behaviour. Our results do not support this hypothesis. Parents reduced their nest visit rate over the course of the day, but offspring did not fledge earlier when their parents decreased their visit rate more strongly with time of day. In conclusion, our results do not support the notion that the time of fledging affects survival but suggest a link with nestling development. • In altricial birds, nestlings typically fledge early in the day. • This is often assumed to improve survival, but with little supporting evidence. • We monitored the precise fledging times of 1582 blue tits from 230 nests. • Fledging time was not associated with the probability of local survival. • Instead, fledging time was related to the developmental stage of nestlings. [ABSTRACT FROM AUTHOR]

The fore‐ and hindlimbs of birds are specialized to perform different functions. The growth patterns of limb bones and their relationship with the ontogeny of locomotion are critical to our understanding of variation in morphological, physiological and life‐history traits within and among species. Unfortunately, the ontogenetic development of limb bones has not been well explored, especially in altricial birds. In this study, we sampled the entire measurements of the pigeon (Columba livia) of individual skeletons, to investigate the ontogenetic allometry of limb bones by reduced major axis regression. The ulna and humerus were found to be positively allometric in relation to body mass, with the ulna growing more rapidly than the humerus. Together with previous data, this suggests that strong positive allometric growth in forelimb bones could be a common trend among diverse Carinatae groups. Hindlimb was dominated by positive allometry, but was variable in the growth of the tarsometatarsus which included three allometric patterns. A greater dorsoventral diameter in the midsection of the humerus and ulna confers superior bending resistance and is ideal for flapping/gliding flight. Shape variation in the midsection of different hindlimb components reflects different mechanical loading, and the markedly inverse trend between the tibiotarsus and tarsometatarsus before 28 days of age also suggests loading change before fledging. Before fledging, the growth of the leg bones was prior to that of the wing bones. This kind of asynchronous development of the fore‐ and hindlimbs was associated with the establishment and improvement of different functions, and with shifts in the importance of different functions over time. [ABSTRACT FROM AUTHOR]

Nesting localities of extant birds and reptiles may provide taphonomic models for interpreting nesting sites of ancient archosaurs. Here we describe assemblages of nesting gulls (Larus delawarensis and L. californicus), American white pelicans (Pelecanus erythrorhynchos), and double-crested cormorants (Phalacrocorax auritus). Seventy nests yielded 2752 skeletal elements and 2308 eggshells. Most material was located inside the nest for gulls and consisted of osteologically mature gull bones and pelican eggshell. Pelican and cormorant nesting material were located outside the nest, with higher percentages of juvenile avian bone. Eggshell concave up and down ratios on the surface of gull nests compared closely to predated assemblages. Pelican and cormorant surface ratios were approximately 50:50, suggesting trampling by altricial young. Weathered bones in the subsurface of cormorant and pelican nests and layers of predated eggshell in gull nests suggest multi-year accumulations. The amount of material associated with the nests and the age of the nester's bones provides a means of distinguishing altricial and semi-precocial nesting sites. Nesting grounds for gulls with semi-precocial young yielded less skeletal material but a higher proportion of mature gull bones, whereas the large assemblages with altricial pelican and cormorant nests were dominated by prey items and their own young. [ABSTRACT FROM AUTHOR]

Levels of conspecific brood parasitism (CBP) and quasi-parasitism (QP) are important parameters for the general understanding of alternative female mating strategies. We deployed double-digest RAD sequencing to assess CBP and QP in a south temperate population of Grass Wrens (Cistothorus platensis). CBP rate was low and varied annually (0–10%). No cases of QP were identified in our population. Grass Wrens showed similar levels of CBP when compared to other Neotropical songbirds. Given that females could increase their reproductive output by laying eggs in both their nests and in other females' nests, it is striking that CBP is so rare. Future work should evaluate counter-adaptations (egg pecking and rejection, nest desertion, and retaliation) that reduce the success of CBP. [ABSTRACT FROM AUTHOR]

Life history theory predicts that physiological and behavioral responsiveness to stress should be delayed in development until the benefits of heightened reactivity outweigh the costs of potentially chronic glucocorticoid levels. Birds often acquire stress‐responsiveness at locomotor independence, however, both stress‐responsiveness and locomotor ability are delayed in birds with altricial developmental strategies. Parrots (Psittacidae) are extremely altricial, but it is not known whether they also postpone physiological responsiveness to stress until locomotor independence. We quantified individual variation in baseline and stress‐induced plasma corticosterone (CORT) concentrations, the main avian glucocorticoid, in wild green‐rumped parrotlets (Forpus passerinus) of Venezuela at four stages of nestling development. Parrotlet neonates are very underdeveloped and compete for parental care among extreme sibling size hierarchies, a competitive scenario that might benefit from early hypothalamic–pituitary–adrenal (HPA) functionality. Nestlings that underwent a standardized restraint stress‐treatment showed higher average CORT concentrations compared to baseline in all age groups sampled, and exhibited no evidence of age‐related changes in the stress response. This is 2 weeks before locomotor independence and earlier than previously documented for altricial species. Results suggest that precocity of HPA function may be advantageous to growth and survivorship in extremely altricial birds. Research Highlight: Green‐rumped parrotlet nestlings exhibited elevated plasma corticosterone concentrations in response to a standardized stress‐treatment by as early as 13 days posthatching of a 30‐day nestling period.Nestlings exhibited no age‐related changes in the stress response at 18, 23, and 28 days of age.Results suggest that parrotlets attain hypothalamic–pituitary–adrenal functionality at an earlier life history stage than previously predicted for altricial birds. [ABSTRACT FROM AUTHOR]

The altricial–precocial spectrum describes the degree of morphological maturation of offspring at the moment of hatching. In fishes, precocial species develop all their structures at early stages of embryogenesis and larvae hatch at an advanced stage of development, while altricial species hatch at a less developed stage. The timing of retinal development also varies significantly between precocial and altricial fish species. Thus, retinal development is completed before hatching in precocial species. In contrast, a relatively simple retina is observed in altricial newborns and the acquisition of the adult retinal features extends until late in larval life. Therefore, retinal maturation at hatching could be considered as a morphological character to describe the developmental mode of fish newborns. Syngnathids fishes hatch with well-developed sensory systems, jaws, and feeding structures and, therefore, they are considered as precocial fish species. Using as a model the retina of two species of syngnathids (Syngnathus typhle and Hippocampus guttulatus), we describe the retinal maturity during different embryological stages and compare the results with previous studies in the retina of other altricial and precocial fish species. This will be done through a review of the pertinent literature, as well as by drawing on our own experience gathered through recent studies on fish retinogenesis. These differences in the maturity of the visual system have implications for the vision-based survival skills during the early life stages after hatching and for the overall ecology and fitness of the species. [ABSTRACT FROM AUTHOR]

Cardiovascular maturation in avian species has primarily been studied in precocial species of birds, with few studies conducted on altricial species, which make up the majority of avian species. In the precocial species of birds studied to date, cardiovascular regulation is derived primarily from an adrenergic receptor stimulation that is present from approximately 50% to 60% of incubation until hatching. Conversely, the cholinergic modulation of heart rate differs in its timing of activation, as it is reported to be present in some studies at 60% of incubation to as late as after hatching in others. This has led to the speculation that, although adrenergic stimulation is critical to cardiovascular homeostasis, cholinergic stimulation prior to hatching in birds is species-specific and therefore is not critical for cardiovascular homeostasis in embryonic birds. In this work, we conducted a series of studies on an altricial species, the neotropic cormorant (Phalacrocorax brasilianus), to gain novel data regarding cardiovascular development in a largely unstudied group of birds. We investigated cholinergic and adrenergic receptor mediated control of both arterial blood pressure and heart rate. We predicted that, given the state of this altricial species at hatching, both cholinergic and adrenergic tone on the cardiovascular system would be functional in the embryo. Our findings indicate that cholinergic tone was present at 90% of incubation. However, there was a pronounced adrenergic tone on the cardiovascular system that was relatively greater than that reported in the other studies of avian embryos. Therefore, our findings support our prediction regarding the function of cholinergic tone and adrenergic tone prior to hatching. • Neotropic cormorant embryos at 70% and 90% of incubation possessed a b-adrenergic tone on arterial pressure and heart rate. • Neotropic cormorant embryos also showed a continuous a-adrenergic tone on arterial pressure. • Cholinergic tone was only present on heart rate at 90% incubation. • Our findings provide further evidence that adrenergic regulation is critical for maintaining homeostasis of the cardiovascular system during embryonic avian development. [ABSTRACT FROM AUTHOR]

Family life forms an integral part of the life history of species across the animal kingdom and plays a crucial role in the evolution of animal sociality. Our current understanding of family life, however, is almost exclusively based on studies that (i) focus on parental care and associated family interactions (such as those arising from sibling rivalry and parent‐offspring conflict), and (ii) investigate these phenomena in the advanced family systems of mammals, birds, and eusocial insects. Here, we argue that these historical biases have fostered the neglect of key processes shaping social life in ancestral family systems, and thus profoundly hamper our understanding of the (early) evolution of family life. Based on a comprehensive survey of the literature, we first illustrate that the strong focus on parental care in advanced social systems has deflected scrutiny of other important social processes such as sibling cooperation, parent–offspring competition and offspring assistance. We then show that accounting for these neglected processes – and their changing role over time – could profoundly alter our understanding of the origin and subsequent evolution of family life. Finally, we outline how this 'diachronic' perspective on the evolution of family living provides novel insights into general processes driving the evolution of animal sociality. Overall, we infer that the explicit consideration of thus‐far neglected facets of family life, together with their study across the whole diversity of family systems, are crucial to advance our understanding of the processes that shape the evolution of social life. [ABSTRACT FROM AUTHOR]

In oviparous species, the embryonic environment-particularly temperature-can alter phenotype and survival of an individual by affecting its size as well as its metabolic rate. Previous studies have shown that incubation temperatures can affect sex ratio in birds; specifically, low incubation temperatures were shown to produce a male-biased sex ratio in zebra finches (Taeniopygia guttata) possibly because of a higher pre- or postnatal mortality rate in females. We hypothesized that sexes respond differently to suboptimal incubation temperature, leading to a male-biased sex ratio. To test this hypothesis, zebra finch eggs were incubated at 36.1°, 37.5°, or 38.5°C and hatching success, hatchling mass, residual yolk mass, and pectoralis mass were measured. We found that while hatchling mass was similar between the sexes at 37.5°C, female hatchlings were heavier at 36.1°C, and male hatchlings were heavier at 38.5°C. Pectoralis muscle mass was similar between the sexes at 36.1°C; however, at 37.5°C, female pectoralis mass was heavier at hatching than that of males. Females at 37.5°C also had lower residual yolk at hatching compared with males, reflecting a higher use of energy by female embryos compared with male embryos at this temperature. In contrast, residual yolk was similar between the sexes at 36.1° and 38.5°C. Our results suggest that there are sex differences in how incubation temperature alters organ mass and yolk energy reserve; this can lead to a difference in survival at different incubation temperatures between the sexes. Taken together with previous studies showing that females alter incubation behavior with ambient temperature, rising ambient temperatures could impact phenotype and survival of avian offspring in a sex-specific manner. [ABSTRACT FROM AUTHOR]

Abstract: Comparative developmental studies have shown that the retina of altricial fish and mammals is incompletely developed at birth, and that, during the first days of life, maturation proceeds rapidly. In contrast, precocial fish and mammals are born with fully differentiated retinas. Concerning birds, knowledge about retinal development is generally restricted to a single order of precocial birds, Galliformes, due to the fact that both the chicken and the Japanese quail are considered model systems. However, comparison of embryonic pre‐hatchling retinal development between altricial and precocial birds has been poorly explored. The purpose of this study was to examine the morphogenesis and histogenesis of the retina in the altricial zebra finch (Taeniopygia guttata, Vieillot 1817) and compare the results with those from previous studies in the precocial chicken. Several maturational features (morphogenesis of the optic vesicle and optic cup, appearance of the first differentiated neurons, the period in which the non‐apical cell divisions are observable, and the emergence of the plexiform layers) were found to occur at later stages in the zebra finch than in the chicken. At hatching, the retina of T. guttata showed the typical cytoarchitecture of the mature tissue, although features of immaturity were still observable, such as a ganglion cell layer containing many thick cells, very thin plexiform layers, and poorly developed photoreceptors. Moreover, abundant mitotic activity was detected in the entire retina, even in the regions where the layering was complete. The circumferential marginal zone was very prominent and showed abundant mitotic activity. The partially undifferentiated stage of maturation at hatching makes the T. guttata retina an appropriate model with which to study avian postnatal retinal neurogenesis. [ABSTRACT FROM AUTHOR]

Endothermy is a conspicuous and important adaptation in birds. Even though juvenile and adult birds are endothermic and maintain a constant, high body temperature by means of internal heat production, they begin life expressing an ectothermic phenotype. Depending on where a species falls along a continuum of maturity at hatching, from precocial to altricial, they begin to express endothermic traits either close to the time of hatching or as nestlings over a period of 1-3 weeks. Developing endothermy requires attaining a high basal metabolic rate and associated aerobic scope to produce sufficient internal heat, insulation to retain the internally produced heat, and a thermostat that “turns on” heat production in response to cooling ambient temperatures. To support the high metabolic costs of endothermy, the animal must have the capacity to deliver sufficient oxygen and nutrients to the heat-generating tissues. In this review, we examine the development of physiological and morphological traits that are required for endothermy and discuss their potential to limit the development of endothermy. These include ventilatory and cardiovascular function, contribution of visceral organ masses, membrane lipid composition, substrate supply pathways, and skeletal muscle physiology. The developmental trajectories of each of these systems in precocial and altricial species can have significant effects on the development of an endothermic phenotype. [ABSTRACT FROM AUTHOR]

Summary: Sleep deprivation during pregnancy is an emerging concern, as it can adversely affect the development of the offspring brain. This study was conducted to evaluate the effects of deprivation of rapid eye movement (REM) sleep during the third term of pregnancy on the sleep–wake profiles of neonates in the Wistar rat model. Sleep–wake patterns were assessed through electrophysiological measures and behavioural observations during postnatal days 1–21 on pups born to REM sleep‐deprived dams and control rats. Pups of REM sleep‐deprived dams had active sleep that was not only markedly higher in percentage during all the days studied, but also had reduced latency during later postnatal days 15–21. Quiet sleep and wake periods were lower. These factors, along with less frequent but longer sleep–wake cycles, indicated maturational delay in the sleep–wake neural networks. The disruption of time‐bound growth of sleep–wake neural networks was substantiated further by the decreased slope of survival plots in the sleep bouts. Examination of altered sleep–wake patterns during early development may provide crucial information concerning deranged neural development in the offspring. This is the first report, to our knowledge, to show that maternal sleep deprivation during pregnancy can delay and impair the development of sleep–wake profile in the offspring. [ABSTRACT FROM AUTHOR]

In chicken, corticotropin-releasing hormone (CRH) acts as a thyrotropin (TSH)-releasing factor, mediated by the type 2 CRH receptor (CRHR2) on the thyrotropes of the pituitary gland. It is not known whether CRH also controls TSH release in non-precocial avian species that have a different pattern of thyroidal activity during their life cycle. Therefore, we investigated the TSH-releasing capacity of CRH in an altricial species, the zebra finch ( Taeniopygia guttata ). Cellular localisation of type 1 CRH receptor ( CRHR1 ) and CRHR2 mRNA in the pituitary was determined by in situ hybridisation, combined with immunohistochemical staining of pituitary thyrotropes. In addition, isolated pituitary glands were stimulated with CRH to determine the effect on TSH release. Lastly, the mRNA levels of hormones and receptors involved in the control of thyroidal and adrenal function were measured by qPCR in zebra finch chicks between hatching and fledging, and in adults. Most of the hypophyseal CRHR2 mRNA co-localised with thyrotropes, whereas CRHR1 mRNA was found inbetween thyrotropes. Pituitary glands stimulated in vitro with CRH showed increased secretion of TSH-like activity. Pituitary CRHR2 mRNA expression decreased while pituitary TSHB mRNA and brain CRH mRNA levels increased towards fledging, similar as seen in chicken hatching. These results suggest that CRHR2 expressed on thyrotropes is likely mediating CRH-induced TSH release in altricial avian species like it does in precocial species, and that the increased thyroid hormone levels towards fledging in altricial birds are the result of increased hypothalamic stimulation, in which the thyrotropic activity of CRH may initially play a role. [ABSTRACT FROM AUTHOR]

The existing different modes of reproduction in monotremes, marsupials and placentals are the main source for our current understanding of the origin and evolution of the mammalian reproduction. The reproductive strategies and, in particular, the maturity states of the neonates differ remarkably between the three groups. Monotremes, for example, are the only extant mammals that lay eggs and incubate them for the last third of their embryonic development. In contrast, marsupials and placentals are viviparous and rely on intra-uterine development of the neonates via choriovitelline (mainly marsupials) and chorioallantoic (mainly placentals) placentae. The maturity of a newborn is closely linked to the parental care strategy once the neonate is born. The varying developmental degrees of neonates are the main focus of this study. Monotremes and marsupials produce highly altricial and nearly embryonic offspring. Placental mammals always give birth to more developed newborns with the widest range from altricial to precocial. The ability of a newborn to survive and grow in the environment it was born in depends highly on the degree of maturation of vital organs at the time of birth. Here, the anatomy of four neonates of the three major extant mammalian groups is compared. The basis for this study is histological and ultrastructural serial sections of a hatchling of Ornithorhynchus anatinus (Monotremata), and neonates of Monodelphis domestica (Marsupialia), Mesocricetus auratus (altricial Placentalia) and Macroscelides proboscideus (precocial Placentalia). Special attention was given to the developmental stages of the organs skin, lung, liver and kidney, which are considered crucial for the maintenance of vital functions. The state of the organs of newborn monotremes and marsupials are found to be able to support a minimum of vital functions outside the uterus. They are sufficient to survive, but without capacities for additional energetic challenges. The organs of the altricial placental neonate are further developed, able to support the maintenance of vital functions and short-term metabolic increase. The precocial placental newborn shows the most advanced state of organ development, to allow the maintenance of vital functions, stable thermoregulation and high energetic performance. The ancestral condition of a mammalian neonate is interpreted to be similar to the state of organ development found in the newborns of marsupials and monotremes. In comparison, the newborns of altricial and precocial placentals are derived from the ancestral state to a more mature developmental degree associated with advanced organ systems. [ABSTRACT FROM AUTHOR]

Hatching asynchrony occurs primarily as a consequence of the timing of embryonic development. Despite over 50 years of study, it is unclear why, ultimately, most birds initiate embryonic development (incubation) before all eggs are laid. One hypothesis focuses on prehatching (embryo) survival and predicts that early incubation maximizes embryo survival by reducing exposure of unincubated eggs (egg viability hypothesis). Another set of hypotheses focuses on posthatching growth and survival and predicts that females time incubation to maximize the number or quality of hatched offspring that fledge (adaptive hatching pattern hypotheses). I experimentally manipulated when females could begin incubation to test how timing of embryonic development influences prehatching survival and posthatching growth and survival in the house sparrow, Passer domesticus . Despite high embryo survival in both naturally asynchronous and experimentally synchronized nests, early incubation appeared to maximize embryo survival in all but the earliest-laid eggs, suggesting that house sparrows begin incubation too late to maximize survival of all embryos. Early incubation had little effect on overall (i.e. mean) patterns of posthatching growth and survival. However, early incubation increased the initial variation in offspring size because last-hatched young were relatively small when all eggs had completed hatching. Nestlings that were small at hatch completion grew slowly and exhibited a reduced probability of survival, suggesting that house sparrows begin incubation too early to maximize growth and survival of hatched offspring. These results suggest that timing of incubation neither maximizes embryo survival nor maximizes posthatching growth and survival. Instead, early incubation appears to be a trade-off between maintaining both embryo survival and growth and survival of late-hatched offspring. Thus, house sparrow females likely time incubation as an adaptive strategy to maximize the number of embryos that survive the incubation and nestling periods to fledge. [ABSTRACT FROM AUTHOR]

In altricial birds, parental provisioning is plastic and can respond to a variety of environmental stimuli. In this study, we manipulated the size of entrances into artificial nest cavities (i.e. nestboxes) in a population of house wrens Troglodytes aedon as a means of manipulating a male's sexual attractiveness, and examined changes in parental provisioning. Nest cavities with large entrances are less desirable as nesting sites, and the males at these sites are less attractive to females. Therefore, we predicted that males at boxes that had large entrances would invest more in parental care (i.e. those that succeeded in finding a mate would provision their offspring at a higher rate) than males at nestboxes with small entrances. As predicted, males provisioned their offspring with food at the highest rates at nestboxes with enlarged entrances, and male provisioning effort positively predicted the number of fledglings they produced per egg. Males at these boxes provisioned more than their mates and more than females and males at nestboxes with small entrances. At nestboxes with small entrances, males provisioned at the same rate as females, and female provisioning did not differ significantly between treatments, on average. Male and female provisioning rates were negatively correlated, such that the increase in provisioning by males at nestboxes with enlarged entrances did not enhance nestling condition, likely because food delivery by females declined with increased provisioning by males. However, the amount of time females spent providing warmth for their ectothermic young increased with increases in male provisioning, suggesting that levels of male parental care altered the mode, not necessarily the extent, of care provided by females. These findings suggest that male provisioning is related to sexual attractiveness, and that sexual conflict over biparental care may not be as simple as the assessment of food provisioning might otherwise suggest. [ABSTRACT FROM AUTHOR]

We evaluated the variation in absolute size and shape of birds' eggs and the effects of developmental mode and phylogenetic relatedness on these traits. Eggs were characterized by length, diameter, and three indices of egg shape. Indices of egg shape were calculated as the ratio of radii that described the curvature of pointed end (cloacal zone), blunt end (infundibular zone), and lateral zone to egg diameter. We found that eggs shape was less variable than the absolute size of eggs. Index of the cloacal zone was the most changeable and index of the infundibular zone was very conservative. Size and shape of eggs could be better explained with phylogenetic relatedness than developmental mode. [ABSTRACT FROM AUTHOR]

The aim of this work is to estimate the relationship between developmental mode and flight style, body mass and wing morphology of birds. We revealed high evolutionary correlation between developmental mode and flight style of birds. Different developmental modes, as well as flight styles, repeatedly appeared in birds' evolution. Precocial birds are associated with continuous-flapping flight. Small altricial birds mostly use passerine-type flight. Soaring birds are large and have an intermediate developmental mode. Developmental strategies and flight styles correlate with differences in body mass and traits of wing morphology (wingspan, wing area, humerus, ulna, manus, and primary feather lengths). Nevertheless, by comparing results of phylogenetic and standard discriminant function analyses, we reveal that phylogeny strongly affects the morphology of wing traits and body mass in birds. When using phylogenetic t-tests, we did not find an association between relative length of wing elements and different developmental mode and flight style groups, except altricial birds with flapping and gliding flight style (Apodidae, Hirundinidae). [ABSTRACT FROM AUTHOR]

In vertebrates, exposure to stressful stimuli early in development may alter the activity of the hypothalamo-pituitaryadrenal (HPA) axis, with the potential for fitness consequences later in life. For altricial species, whose young rely on their parents for food, warmth, and protection from predators, adult behavior can modify the impact of some stressors on their offspring after birth or hatching. We have shown that single bouts of cooling that normally occur when brooding females leave the nest elevate corticosterone secretion in very young free-living eastern bluebird (Sialia sialis) chicks. Thus, natural variation in maternal brooding patterns can result in differential exposure of offspring to cooling, and also to glucocorticoids, very early in development. We tested the hypothesis that exposure to repeated bouts of cooling (mimicking those that occur normallywhen females leave the nest)would alter the activity of the chicks' HPA axis later in life. We exposed freeliving chicks to either four 18-min bouts of cooling or brooding temperatures (control) during the first week after hatching. Then, just before fledging (i.e., at least 7 d after the cooling treatments had ceased), we assessed their corticosterone responses to restraint. Repeatedly cooled chicks had a significantly lower corticosterone response to restraint than did control chicks but did not differ from controls in other measures of growth and development. Our data suggest that natural variation in maternal brooding patterns, and hence natural variation in the chicks' body temperature, can alter the activity of the HPA axis well beyond the brooding period. [ABSTRACT FROM AUTHOR]

Background: a series of events take place in a precise spatial and temporal context during the development of any organism. Typically, certain ontogenetic processes are consistent with the proper completion of previous events. Objective: to identify possible heterochronic events that may relate to altricial and precocious development patterns. Methods: we analyzed the ontogeny of three species of birds with two different development models: Columba livia (semialtricial 2), Coturnix coturnix, and Gallus gallus domesticus (precocial 2). The starts and endings of thirteen morphological events were compared, from hour 16 of incubation to the time of hatching. Results: while no differences in the sequence of developmental events were found, the events of the maturation stage in the altricial kind started earlier compared to the precocial species. Ontogenetic acceleration events in C. livia and C. coturnix explain how these species reach a level of morphological development similar to that of G. gallus domesticus, but with shorter incubation period. Conclusion: the results provide information not considered in the literature of the specialty about heterochronic events in early developmental stages of poultry. [ABSTRACT FROM AUTHOR]

We examined development of endothermy in altricial Red-winged Blackbirds ( Agelaius phoeniceus) by measuring oxygen consumption $$(\dot{V}{\text{o}}_{2} )$$ , body temperature and ventilation at ambient temperatures from 35 to 15 °C. Mitochondrial respiration of permeabilized skeletal muscle was also measured from breast (pectoralis) and thigh (femorotibialis) muscles. Animals were studied from the first day of hatching through fledging (12 days post-hatch, dph). Nestling whole-body metabolic rate began to show an endothermic response to cold temperature midway between hatching and fledging. Nestlings less than 5 dph were unable to maintain elevated $$\dot{V}{\text{o}}_{2}$$ and body temperature when exposed to gradually decreasing temperature, whereas 7 dph nestlings maintained $$\dot{V}{\text{o}}_{2}$$ until ~25 °C, after which $$\dot{V}{\text{o}}_{2}$$ decreased. From 10 dph to fledging, animals maintained elevated $$\dot{V}{\text{o}}_{2}$$ and body temperature when exposed to gradual cooling; full endothermic capacity was achieved. Ventilation followed a similar developmental trend to that of $$\dot{V}{\text{o}}_{2}$$ , with increases in 10 dph fledglings occurring in tidal volume rather than ventilation frequency. LEAK respiration and oxidative phosphorylation (OXPHOS) through complex I of breast muscle mitochondria increased significantly after 3 dph. Expression of avUCP and PCG- 1α mRNA increased significantly at 3 dph and remained elevated in both skeletal muscle types. Increased metabolic capacity at the cellular level occurred prior to that of the whole animal. This change in whole animal metabolic capacity increased steadily upon hatching as evidenced by the shift of metabolic rate from an ectothermic to endothermic phenotype and the increase of mitochondrial OXPHOS activity of the shivering muscles of this altricial avian species. [ABSTRACT FROM AUTHOR]

In birds, incubation temperature can vary by several degrees Celsius among nests of a given species. Parents may alter incubation temperature to cope with environmental conditions and/or to manipulate embryonic development, and such changes in incubation behavior could have long-lasting effects on offspring phenotype. To investigate short- and long-term effects of suboptimal incubation temperatures on survival and physiological functions in zebra finches, eggs were incubated at 36.2, 37.4 or 38.4°C for the entire incubation period. The post-hatch environment was identical among the treatment groups. We found that hatching success was lowest in the 38.4°C group, while post-hatch survival was lowest in the 36.2°C group. Incubation temperature had sex-specific effects on offspring phenotype: incubation temperatures affected body mass (Mb) but not physiological parameters of males and conversely, the physiological parameters but not Mb of females. Specifically, males from the 38.4°C group weighed significantly less than males from the 36.2°C group from the nestling period to adulthood, whereas females from different incubation temperature groups did not differ in Mb. In contrast, females incubated at 36.2°C had transient but significantly elevated basal metabolic rate and adrenocortical responses during the nestling and fledgling periods, whereas no treatment effect was observed in males. Innate immunity was not affected by incubation temperature in either sex. These results suggest that a 1°C deviation from what is considered an optimal incubation temperature can lower offspring performance and offspring survival. [ABSTRACT FROM AUTHOR]

Accurate estimations of nestling ages are often required for studies of life history traits and breeding strategies of avian species. Yet detailed information on species-specific developmental patterns of chicks is scarce. In this study, we present comprehensive data on plumage and behavioural development of New Zealand fantail (Rhipidura fuliginosa placabilis) chicks during the nesting period. We also provide an illustrated guide to ageing New Zealand fantail nestlings using visual traits, based on the daily development characteristics of 15 broods. This study contributes towards understanding the life history of this species as well as forming a foundation for future comparative studies on avian life history. [ABSTRACT FROM AUTHOR]

Highlights: [•] We studied the effects of cooling on corticosterone secretion in bluebird chicks. [•] A<10°C reduction of chick surface temperature elevated corticosterone secretion. [•] Thermal and hormonal responses to cooling increased in an age-dependent manner. [•] Some broods naturally experienced such bouts of cooling in the wild. [•] Variation in maternal brooding may affect glucocorticoid exposure early in life. [ABSTRACT FROM AUTHOR]

The avian eggshell acts as the major source of calcium for embryogenesis in bird. Using scanning electron microscopy, the inner eggshell surface was analysed before and after embryonic development and its accompanying calcium removal. This was done in eggs from two bird species with different growth rates and modes of development, the precocial Japanese quail Coturnix japonica and the altri-cial starling Sturnus vulgaris. Next, enzyme histochemistry was used to localize carbonic anhydrase in the extra-embryonic chorioallantoic membrane to provide support for the hypothesis that calcium may be released from the eggshell by means of acidification through the action of carbonic anhydrase. However, neither in the precocial quail nor in the altricial starling could any staining for carbonic anhydrase be detected. These results lead us to the conclusion that the role of carbonic anhydrase in embryonic calcium mobilization from the avian eggshell remains unclear. [ABSTRACT FROM AUTHOR]

Abstract: The separation of a nutrition-responsive insulin-like growth factor (IGF) system and a growth hormone (GH) responsive IGF system to control pre- and post-natal growth of developing mammals may originate from the constraints imposed by intra-uterine development. In eutherian species that deliver relatively precocial young, maturation of the GH regulatory system is coincident with the time of birth. We measured the hepatic expression of the four key growth axis genes GH-receptor, IGF-1 and -2, and IGFBBP-3, and plasma protein concentrations of IGF-1 from late fetal life through to adult stages of a marsupial, the tammar wallaby. The data clearly show that maturation of GH-regulated growth in marsupials occurs gradually over the course of post-natal life at an equivalent developmental stage to that of precocial eutherian mammals. This suggests that the timing of GH-regulated growth in marsupials is not related to parturition but instead to the relative developmental stage. [Copyright &y& Elsevier]

Brain size variation in mammals correlates with life histories: larger-brained species have longer gestations, mature later, and have increased lifespans. These patterns have been explained in terms of developmental costs (larger brains take longer to grow) and cognitive benefits (large brains enhance survival and increase lifespan). In support of the developmental cost hypothesis, we show that evolutionary changes in pre- and postnatal brain growth correlate specifically with duration of the relevant phases of maternal investment (gestation and lactation, respectively). We also find support for the hypothesis that the rate of fetal brain growth is related to the energy turnover of the mother. In contrast, we find no support for hypotheses proposing that costs are accommodated through direct tradeoffs between brain and body growth, or between brain growth and litter size. When the duration of maternal investment is taken into account, adult brain size is uncorrelated with other life history traits such as lifespan. Hence, the general pattern of slower life histories in large-brained species appears to be a direct consequence of developmental costs. [ABSTRACT FROM AUTHOR]

The article discusses the importance of neonatal maturity to understand the evolution of brain size in homeothermic vertebrates. The authors argue that the combined field of brain size constraints and tracing brain development techniques has played an important role in the development of an essential framework of brain size evolution. They mention that most people believe that the evolution of large brains is limited by the cost of brain maintenance or brain growth.

The evolution of mammalian brain size is directly linked with the evolution of the brain's unique structure and performance. Both maternal life history investment traits and basal metabolic rate (BMR) correlate with relative brain size, but current hypotheses regarding the details of these relationships are based largely on placental mammals. Using encephalization quotients, partial correlation analyses, and bivariate regressions relating brain size to maternal investment times and BMR, we provide a direct quantitative comparison of brain size evolution in marsupials and placentals, whose reproduction and metabolism differ extensively. Our results show that the misconception that marsupials are systematically smaller-brained than placentals is driven by the inclusion of one large-brained placental clade, Primates. Marsupial and placental brain size partial correlations differ in that marsupials lack a partial correlation of BMR with brain size. This contradicts hypotheses stating that the maintenance of relatively larger brains requires higher BMRs. We suggest that a positive BMR-brain size correlation is a placental trait related to the intimate physiological contact between mother and offspring during gestation. Marsupials instead achieve brain sizes comparable to placentals through extended lactation. Comparison with avian brain evolution suggests that placental brain size should be constrained due to placentals' relative precociality, as has been hypothesized for precocial bird hatchlings. We propose that placentals circumvent this constraint because of their focus on gestation, as opposed to the marsupial emphasis on lactation. Marsupials represent a less constrained condition, demonstrating that hypotheses regarding placental brain size evolution cannot be generalized to all mammals. [ABSTRACT FROM AUTHOR]

Abstract: Neural aromatization of testosterone (T) to estrogen during development is thought to be important for sexual differentiation of many altricial mammals. We evaluated the effects of neonatal injections of the non-aromatizable androgen dihydrotestosterone propionate (DHTP) and estradiol (E2) on the copulatory behavior of the female musk shrew, an altricial insectivore. Following adult ovariectomy and replacement T, animals were paired with a stimulus female for two 60-minute copulatory behavior tests. The latency to induce sexual receptivity (in the form of tail-wagging by the female), mount latency and total number of mounts were recorded in experimental females and in a group of untreated control males. While neither hormone treatment significantly affected mounting behavior, DHTP-treated animals induced receptivity faster and with latencies not significantly different from intact males, suggesting that early non-aromatizable androgens can have masculinizing actions by either increasing sexual motivation or making the treated animal more attractive to the stimulus female. Reliance on androgenic rather than estrogenic metabolites for the differentiation of courtship behaviors conforms to the pattern seen more typically in primates than rodents. [Copyright &y& Elsevier]

Schmidt KL, Chin EH, Shah AH, Soma KK. Cortisol and corticosterone in immune organs and brain of European starlings: developmental changes, effects of restraint stress, comparison with zebra finches. Am J Physiol Regul Integr Comp Physiol 297: R42-R5 I, 2009. First published April 22, 2009; doi: 10.1 152/ajpregu.90964.2008.-Glucocorticoids (GCs) are produced in the adrenal glands and also in extraadrenal sites, including immune organs and brain. Here, we examined regulation of systemic GC levels in plasma and local GC levels in immune organs and brain during development. We conducted two studies and examined a total of 462 samples from 70 subjects. In study 1, we determined corticosterone and cortisol levels in the plasma, immune organs, and brain of wild European starlings on posthatch day 0 (P0) and P10 (at baselihe and after 45 mm of restraint). Baseline corticosterone and cortisol levels were low in the immune organs and brain at P0 and P10, providing little evidence for local GC synthesis in starlings. At P0, restraint had no significant effects on corticosterone or cortisol levels in the plasma or tissues; however, there was a trend for restraint to increase both corticosterone and cortisol in the immune organs. At P10, restraint increased corticosterone levels in the plasma and all tissues, but restraint increased cortisol levels in the plasma, thymus, and diencephalon only. In study 2, we directly compared GC levels in European starlings and zebra finches at P4. In zebra finches but not starlings, cortisol levels were higher in the immune organs than in plastha. This difference in immune GC levels might be due to evolutionary lineage, life history strategy, or experiential factors, such as parasite exposure. This is the first study to measure immune GC levels in wild animals and one of the first studies to measure local GC levels after restraint stress. [ABSTRACT FROM AUTHOR]

Glucocorticoids (GCs) have profound effects on the immune and nervous systems during development. However, circulating GC levels are low neonatally and show little response to stressors. This paradox could be resolved if immune and neural tissues locally synthesize GCs. Here, we measured baseline corticosterone and cortisol levels in plasma, immune organs, and brain regions of developing zebra finches. Steroids were extracted using solid phase-extraction and quantified using specific immunoassays. As expected, corticosterone was the predominant GC in plasma and increased with age. In contrast, cortisol was the predominant GC in immune tissues (bursa of Fabricius, thymus, spleen) and decreased with age. Cortisol levels in immune tissues were higher than cortisol levels in plasma. In the brain, corticosterone and cortisol levels were similarly low, providing little evidence for local synthesis of GCs in the brain. This is the first study to measure 1) cortisol in the plasma of songbirds, 2) corticosterone or cortisol in the brain of songbirds, and 3) corticosterone or cortisol in the immune system of any species. Despite the prevailing dogma that corticosterone is the primary GC in birds, these results indicate that cortisol is the predominant GC in the immune system of developing zebra finches. These results raise the hypothesis that cortisol is synthesized de novo from cholesterol in the immune system as an "immunosteroid," analogous to neurosteroids synthesized in the brain. Local production of GCs in immune tissues may allow GCs to regulate lymphocyte selection while avoiding the costs of high systemic GCs during development. [ABSTRACT FROM AUTHOR]

Developing animals may face a cost-benefit tradeoff during growth mediated through hormones such as glucocorticoids, as the hormone is essential for development but can have detrimental consequences. To investigate potential tradeoffs caused by brief, moderate elevations of corticosterone in avian young, we artificially elevated the hormone levels in two ways: feeding corticosterone-containing worms and applying corticosterone dermal patches. The former experiment tested the effects of an acute corticosterone elevation (25 mm) on begging behavior, whereas the latter explored the effects of artificially elevated corticosterone for 24 to 48 h on growth. Corticosterone altered both begging behavior and growth of white-crowned sparrow nestlings. It increased latency to beg immediately after the treatment and suppressed growth as early as 24 h after the patch application. These experiments also showed that the effects depended on the age or types of development (e.g. gaining mass or growing feathers) that the nestlings were going through. [ABSTRACT FROM AUTHOR]

Abstract: Activation of the adrenocortical response to stress during development can have fundamental consequences over the lifetime of the organism; as such, many organisms are less responsive to stress during critical developmental periods. In this study, we evaluated stress reactivity in nestling white-crowned sparrows, examining corticosterone and binding globulin levels in response to both restraint stress and ACTH challenge. Restraint stress induced a significant corticosterone response in both 4 to 6- and 7 to 9-day-old nestlings, but not in the youngest group (1–3 days); this non-significant increase in corticosterone in the youngest birds resembles the mammalian hyporesponsive period, wherein young animals are resistant to most stressors. Binding globulin levels appear to extend this period of low reactivity: when free corticosterone levels were calculated, only the oldest age group (7–9 day) showed a significant response to restraint. ACTH challenge data revealed that all ages of white-crowned sparrow nestlings responded to exogenous ACTH treatment with significant elevation of corticosterone, although early-stage nestlings did not reach adult levels of response. [Copyright &y& Elsevier]

This article reviews thyroid function and its hypothalamic-pituitary-thyroid (HPT) axis control in birds with emphasis on the similarities and differences in thyroid function compared to mammals and other vertebrate classes. Thyroid hormones are important in metabolism and the thermogenesis required for homeothermy in birds, as in mammals, the other homeothermic class of vertebrates. Thyroid hormones play important roles in development and growth in birds, as is the case for all vertebrate classes. The developmental effects of thyroid hormones in birds are presented in the context of differences in precocial and altricial patterns of development and growth with emphasis on oviparous development. The sections on thyroid hormone actions include discussion of effects on the development of a number of tissue types as well as on seasonal organismal processes and interactions of the thyroid axis with reproduction. The current picture of how environmental chemicals may disrupt avian thyroid function is relatively limited and is presented in the context of the assessment endpoints that have been used to date. These endpoints are categorized as thyroid and HPT axis endpoints versus target organ endpoints. The final section discusses two recommended assay protocols, the avian two-generation toxicity assay and the avian one-generation assay, and whether these protocols can evaluate thyroid disruption in birds. [ABSTRACT FROM AUTHOR]

Abstract: Mammals adopt a limited number of postures during their day-to-day activities. These stereotyped skeletal configurations are functionally adequate and limit the number of degrees of freedom to be controlled by the central nervous system. The temporal pattern of emergence of these configurations in altricial mammals is unknown. We therefore carried out an X-ray study in unrestrained rats from birth (P0) until postnatal day 23 (P23). The X-rays showed that many of the skeletal configurations described in adult rodents were already present at birth. By contrast, limb placement changed abruptly at around P10. These skeletal configurations, observed in anesthetized pups, required the maintenance of precise motor control. On the other hand, motor control continued to mature, as shown by progressive changes in resting posture and head movements from P0 to P23. We suggest that a few innate skeletal configurations provide the necessary frames of reference for the gradual construction of an adult motor repertoire in altricial mammals, such as the rat. The apparent absence of a requirement for external sensorial cues in the maturation of this repertoire may account for the maturation of postural and motor control in utero in precocial mammals (Muir et al., 2000 for a review on the locomotor behavior of altricial and precocial animals). [Copyright &y& Elsevier]

We partitioned the metabolizable energy intake (MEI) into energy for maintenance (MEm) and for growth (MEg) in sucking precocial and altricial rodent pups. Each of the two components includes energy loss due to the heat increment of feeding. MEm of precocial pups expressed as average daily energy costs or as a proportion of MEI was greater than in altricial pups of similar size and, therefore, less energy was available for growth. Consequently, the overall energy cost (via total MEI) per unit postnatal growth of precocial pups was greater than for altricial pups of similar size. We used the proportion of calculated MEm to that predicted by body mass as an index of precociality in rodent pups. The proportion of MEg to MEI in precocial pups was lower than in altricial pups and was inversely related to the index of precociality. [ABSTRACT FROM AUTHOR]

Abstract: During the evolution of therian mammals, the two-segmented, sprawled tetrapod limbs were transformed into three-segmented limbs in parasagittal zig-zag configuration (three-segment limb hypothesis). As a consequence, the functional correspondence of limb segments has changed (now: scapula to thigh, upper arm to shank, fore arm plus hand to foot). Therefore, the scapula was taken into account in the current study of the postnatal growth of the postcranial skeleton in two small mammalian species (Tupaia glis, Galea musteloides). Comparisons were made between the functionally equivalent elements and not in the traditional way between serially homologous segments. This study presents a test of the three-segment limb hypothesis which predicts a greater ontogenetic congruence in the functionally equivalent elements in fore and hind limbs than in the serially homologous elements. A growth sequence, with decreasing regression coefficients from proximal to distal, was observed in both species under study. This proximo-distal growth sequence is assumed to be ancestral in the ontogeny of eutherian mammals. Different reproductive modes have evolved within eutherian mammals. To test the influence of different life histories on ontogenetic scaling during postnatal growth, one species with altricial juveniles (Tupaia glis) assumed to be the ancestral mode of development for eutherians and one species with derived, precocial young (Galea musteloides) were selected. The growth series covered postnatal development from the first successive steps with a lifted belly to the adult locomotory pattern; thus, functionally equivalent developmental stages were compared. The higher number of allometrically positive or isometrically growing segments in the altricial mammalian species was interpreted as a remnant of the fast growth period in the nest without great locomotor demands, and the clearly negative allometry in nearly all segments in the precocial young was interpreted as a response to the demand on early locomotor activity. Different life histories seem to have a strong influence on postnatal ontogenetic scaling; the effects of the developmental differences are still observable when comparing adults of the two species. [Copyright &y& Elsevier]

Comparative studies of locomotion indicate that limb design and performance are very similar in adult mammals of small to medium size. The present study was undertaken to test whether basic therian limb pattern is present during postnatal development. Kinematic data were collected from juveniles of two eutherian species in a cross-sectional study, using cinevideography. The tree shrew Tupaia glis and the cui Galea musteloides were selected because of their different reproductive strategies, which could result in differences in the development of locomotor abilities. The aims of this study were to describe the process by which young animals develop the adult pattern of locomotion and the extent to which this process varies in two species with very different postnatal ontogenies. Despite their different life histories, the development of kinematic parameters in the altricial tree shrew and the precocial cui are surprisingly similar. General limb design, performance, and timing of segment and joint movements in the young animals were similar to adults in both species, even from the first steps. Touch-down of the forelimb occurred at the position below the eye in all individuals and limb position was highly standardized at touch-down; no major changes in segment and joint angles were observed. Significant changes occurred at lift-off. With increasing body mass, limb segments rotated more caudally, which resulted in larger limb excursions and relatively longer steps. Developmental changes in locomotor abilities were similar in both species; only the time necessary to reach the adult performance was different. Despite the widely assumed maturity of locomotor abilities in precocial young, the first steps of the cui juveniles were not similar to the movements of adults. The adult locomotor pattern was reached within the first postnatal week in the cui and by the time they leave the nest in the tree shrew (39 days after birth; individual P39). These results suggest that during the evolution of precocial development only processes independent of exercise or gravity can be shifted into the intrauterine period. However, development of locomotor ability dependents on exercise, and adjustments and training occur during growth. Therefore, only the time necessary to reach maturity was dearly shortened in the precocial juvenile relative to the ancestral altricial condition. [ABSTRACT FROM AUTHOR]

Pelicans produce altricial chicks that develop into some of the largest birds capable of sustained flight. We traced pulmonary morphological development in the Australian pelican, Pelicanus conspicillatus, from third trimester embryos to adults. We described growth and development with allometric relationships between lung components and body mass or lung volume, according to the equation y =  ax b. Pelican lung volume increased faster than body mass ( b = 1.07). Relative to lung volume, the airways and vascular spaces increased allometrically ( b > 1) in embryos, but isometrically ( b ≈ 1) after hatching. Parabronchial mantle volume decreased ( b < 1) prior to hatching and increased isometrically thereafter. Surface area of air capillaries, blood capillaries and the blood–gas barrier increased relative to lung volume ( b > 0.67) before and after hatching. Barrier thickness decreased before hatching, remained constant in juveniles and decreased by adulthood. The anatomical diffusing capacity significantly increased before hatching ( b = 4.44) and after hatching ( b = 1.26). Although altricial pelicans developed pulmonary complexity later than precocial turkeys, the volume-specific characteristics were similar. However, lungs of volant adult pelicans became significantly larger, with a greater capacity for gas exchange, than lungs of terrestrial turkeys. Exchange characteristics of growing pelican lungs were inferior to those of adult birds of 26 other species, but converged with them at maturity. [ABSTRACT FROM AUTHOR]