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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]

In birds, parental care and attachment period differ widely depending on the species (altricial or precocial), developmental strategies, and life history traits. In most bird species, parental care can be provided by both female and male individuals and includes specific stages such as nesting, laying, and hatching. During said periods, a series of neuroendocrine responses are triggered to motivate parental care and attachment. These behaviors are vital for offspring survival, development, social bonding, intergenerational learning, reproductive success, and ultimately, the overall fitness and evolution of bird populations in a variety of environments. Thus, this review aims to describe and analyze the behavioral and endocrine systems of parental care and newborn attachment in birds during each stage of the post-hatching period. [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]

In birds, parental care and attachment period differ widely depending on the species (altricial or precocial), developmental strategies, and life history traits. In most bird species, parental care can be provided by both female and male individuals and includes specific stages such as nesting, laying, and hatching. During said periods, a series of neuroendocrine responses are triggered to motivate parental care and attachment. These behaviors are vital for offspring survival, development, social bonding, intergenerational learning, reproductive success, and ultimately, the overall fitness and evolution of bird populations in a variety of environments. Thus, this review aims to describe and analyze the behavioral and endocrine systems of parental care and newborn attachment in birds during each stage of the post-hatching period.

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]

Epidemiologically, metabolic disorders have garnered much attention, perhaps due to the predominance of obesity. The early postnatal life represents a critical period for programming multifactorial metabolic disorders of adult life. Though altricial rodents are prime subjects for investigating neonatal programming, there is still no sufficiently generalised literature on their usage and methodology. This review focuses on establishing five approach-based models of neonatal rodents adopted for studying metabolic phenotypes. Here, some modelled interventions that currently exist to avoid or prevent metabolic disorders are also highlighted. We also bring forth recommendations, guidelines and considerations to aid research on neonatal programming. It is hoped that this provides a background to researchers focused on the aetiology, mechanisms, prevention and treatment of metabolic disorders. [ABSTRACT FROM AUTHOR]

The visual system is affected by neurodegenerative diseases caused by the degeneration of specific retinal neurons, the leading cause of irreversible blindness in humans. Throughout vertebrate phylogeny, the retina has two kinds of specialized niches of constitutive neurogenesis: the retinal progenitors located in the circumferential marginal zone and Müller glia. The proliferative activity in the retinal progenitors located in the circumferential marginal zone in precocial birds such as the chicken, the commonest bird model used in developmental and regenerative studies, is very low. This region adds only a few retinal cells to the peripheral edge of the retina during several months after hatching, but does not seem to be involved in retinal regeneration. Müller cells in the chicken retina are not proliferative under physiological conditions, but after acute damage some of them undergo a reprogramming event, dedifferentiating into retinal stem cells and generating new retinal neurons. Therefore, regenerative response after injury occurs with low efficiency in the precocial avian retina. In contrast, it has recently been shown that neurogenesis is intense in the retina of altricial birds at hatching. In particular, abundant proliferative activity is detected both in the circumferential marginal zone and in the outer half of the inner nuclear layer. Therefore, stem cell niches are very active in the retina of altricial birds. Although more extensive research is needed to assess the potential of proliferating cells in the adult retina of altricial birds, it emerges as an attractive model for studying different aspects of neurogenesis and neural regeneration in vertebrates.

During development of the vertebrate retina, mitotic activity is defined as apical when is located at the external surface of the neuroepithelium or as non-apical when is found in more internal regions. Apical mitoses give rise to all retinal cell types. Non-apical mitoses are linked to committed horizontal cell precursors that subsequently migrate vitreo-sclerally, reaching their final position in the outer surface of the inner nuclear layer, where they differentiate. Previous studies have suggested differences in the timing of retinal maturation between altricial and precocial bird species. In the present study we analyze qualitatively and quantitatively the mitotic activity in the developing retina of an altricial (zebra finch, Taeniopygia guttata) and a precocial (Japanese quail, Coturnix coturnix) bird species. We found that pHisH3-immunoreactive apical and non-apical mitoses were abundant in the T. guttata retina at the hatching stage. In contrast, pHisH3 immunoreactivity almost disappeared from the quail retina at the embryonic day 10 (E10). Furthermore, we also found that the onset of the appearance of non-apical mitoses occurred at later stages in the altricial bird species than in the precocial one. The disappearance of apical mitoses and the spatiotemporal distribution of non-apical mitoses followed central to peripheral and dorsal to ventral gradients, similar to gradients of cell differentiation described in the retina of birds. Therefore, these results suggest that retinal neurogenesis is active at the hatching stage in T. guttata , and that horizontal cell differentiation is delayed in the altricial bird species compared to the precocial one. Together, this study reveals important insights into the timing differences that regulate bird retinal maturation and provides a better understanding of the evolution of avian altriciality and precociality. [ABSTRACT FROM AUTHOR]

During development of the vertebrate retina, mitotic activity is defined as apical when is located at the external surface of the neuroepithelium or as non-apical when is found in more internal regions. Apical mitoses give rise to all retinal cell types. Non-apical mitoses are linked to committed horizontal cell precursors that subsequently migrate vitreo-sclerally, reaching their final position in the outer surface of the inner nuclear layer, where they differentiate. Previous studies have suggested differences in the timing of retinal maturation between altricial and precocial bird species. In the present study we analyze qualitatively and quantitatively the mitotic activity in the developing retina of an altricial (zebra finch, Taeniopygia guttata) and a precocial (Japanese quail, Coturnix coturnix) bird species. We found that pHisH3-immunoreactive apical and non-apical mitoses were abundant in the T. guttata retina at the hatching stage. In contrast, pHisH3 immunoreactivity almost disappeared from the quail retina at the embryonic day 10 (E10). Furthermore, we also found that the onset of the appearance of non-apical mitoses occurred at later stages in the altricial bird species than in the precocial one. The disappearance of apical mitoses and the spatiotemporal distribution of non-apical mitoses followed central to peripheral and dorsal to ventral gradients, similar to gradients of cell differentiation described in the retina of birds. Therefore, these results suggest that retinal neurogenesis is active at the hatching stage in T. guttata, and that horizontal cell differentiation is delayed in the altricial bird species compared to the precocial one. Together, this study reveals important insights into the timing differences that regulate bird retinal maturation and provides a better understanding of the evolution of avian altriciality and precociality.

Many songbirds begin active incubation after laying their penultimate egg, resulting in synchronous hatching of the clutch except for a last-hatched individual ("runt") that hatches with a size deficit and competitive disadvantage to siblings when begging for food. However, climate change may elevate temperatures and cause environmental incubation as eggs are laid, resulting in asynchronous hatching and larger size hierarchies among siblings. Although previous work demonstrated that asynchronous hatching reduces nestling growth and survival relative to synchrony, the physiological mechanisms underlying these effects are unclear. To test the effects of asynchronous hatching on runt growth, survival, physiology, and compensatory growth-related tradeoffs, we manipulated incubation temperature in nest boxes of European starlings (Sturnus vulgaris) to increase asynchronous hatching and collected nestling morphological measurements and blood samples to assess physiology and development. Independent of heating treatment, runts from asynchronously hatched nests had lower survival than runts from more synchronous nests. Surviving runts from asynchronous nests were smaller and had reduced stress-induced corticosterone concentrations and reduced circulating glucose compared with runts from synchronous nests. Despite persistent size and energy deficits, runts from asynchronous nests did not have significant deficits in immunity or telomere length when compared with runts from synchronous nests, suggesting no trade-off between investment in immune development or telomere maintenance with growth. Overall, these results suggest that increased asynchrony due to climate change could reduce clutch survival for altricial songbirds, especially for the smallest chicks in a clutch, and that the negative effects of asynchrony may be driven by persistent energetic deficits., (© 2024 Wiley Periodicals LLC.)

Birds can be classified into altricial and precocial species. The hatchlings of altricial birds cannot stand, whereas precocial birds can walk and run soon after hatching. It might be owing to the development of the hindlimb bones in the embryo stage, but the molecular regulatory basis underlying the divergence is unclear. To address this issue, we chose the altricial pigeon and the precocial Japanese quail as model animals. The data of tibia weight rate, embryonic skeletal staining, and tibia tissues paraffin section during the embryonic stage showed that the Japanese quail and pigeon have similar skeletal development patterns, but the former had a faster calcification rate. We utilized the comparative transcriptome approach to screen the genes and pathways related to this heterochronism. We separately analyzed the gene expression of tibia tissues of quail and pigeon at two consecutive time points from an inability to stand to be able to stand. There were 2910 differentially expressed genes (DEGs) of quail, and 1635 DEGs of pigeon, respectively. A total of 409 DEGs in common in the quail and pigeon. On the other hand, we compared the gene expression profiles of pigeons and quails at four time points, and screened out eight pairs of expression profiles with similar expression trends but delayed expression in pigeons. By screening the common genes in each pair of expression profiles, we obtained a gene set consisting of 152 genes. A total of 79 genes were shared by the 409 DEGs and the 152 genes. Gene Ontology analysis of these common genes showed that 21 genes including the COL gene family (COL11A1, COL9A3, COL9A1), IHH, MSX2, SFRP1, ATP6V1B1, SRGN, CTHRC1, NOG, and GDF5 involved in the process of endochondral ossification. These genes were the candidate genes for the difference of tibial development between pigeon and quail. This is the first known study on the embryo skeletal staining in pigeon. It provides some new insights for studying skeletal development mechanisms and locomotor ability of altricial and precocial bird species.

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]

Mammals are born on a precocial–altricial continuum. Altricial species produce helpless neonates with closed distant organs incapable of locomotion, whereas precocial species give birth to well-developed young that possess sophisticated sensory and locomotor capabilities. Previous studies suggest that distinct patterns of cortex development differ between precocial and altricial species. This study compares patterns of neocortex neurogenesis and maturation in the precocial guinea pig and altricial dwarf rabbit, both belonging to the taxon of Glires. We show that the principal order of neurodevelopmental events is preserved in the neocortex of both species. Moreover, we show that neurogenesis starts at a later postconceptional day and takes longer in absolute gestational days in the precocial than the altricial neocortex. Intriguingly, our data indicate that the dwarf rabbit neocortex contains a higher abundance of highly proliferative basal progenitors than the guinea pig, which might underlie its higher encephalization quotient, demonstrating that the amount of neuron production is determined by complex regulation of multiple factors. Furthermore, we show that the guinea pig neocortex exhibits a higher maturation status at birth, thus providing evidence for the notions that precocial species might have acquired the morphological machinery required to attain their high functional state at birth and that brain expansion in the precocial newborn is mainly due to prenatally initiating processes of gliogenesis and neuron differentiation instead of increased neurogenesis. Together, this study reveals important insights into the timing and cellular differences that regulate mammalian brain growth and maturation and provides a better understanding of the evolution of mammalian altriciality and presociality.

Mammals are born on a precocial–altricial continuum. Altricial species produce helpless neonates with closed distant organs incapable of locomotion, whereas precocial species give birth to well-developed young that possess sophisticated sensory and locomotor capabilities. Previous studies suggest that distinct patterns of cortex development differ between precocial and altricial species. This study compares patterns of neocortex neurogenesis and maturation in the precocial guinea pig and altricial dwarf rabbit, both belonging to the taxon of Glires. We show that the principal order of neurodevelopmental events is preserved in the neocortex of both species. Moreover, we show that neurogenesis starts at a later postconceptional day and takes longer in absolute gestational days in the precocial than the altricial neocortex. Intriguingly, our data indicate that the dwarf rabbit neocortex contains a higher abundance of highly proliferative basal progenitors than the guinea pig, which might underlie its higher encephalization quotient, demonstrating that the amount of neuron production is determined by complex regulation of multiple factors. Furthermore, we show that the guinea pig neocortex exhibits a higher maturation status at birth, thus providing evidence for the notions that precocial species might have acquired the morphological machinery required to attain their high functional state at birth and that brain expansion in the precocial newborn is mainly due to prenatally initiating processes of gliogenesis and neuron differentiation instead of increased neurogenesis. Together, this study reveals important insights into the timing and cellular differences that regulate mammalian brain growth and maturation and provides a better understanding of the evolution of mammalian altriciality and presociality. [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]

Most mammals and birds are altricial, small and naked at birth/hatching. They attain endothermic thermoregulation at a fraction of their adult size at a vulnerable stage with high heat loss when many could profit from using torpor for energy conservation. Nevertheless, detailed data on the interrelations between torpor expression and development of endothermic thermoregulation are currently restricted to 90%, followed by endothermic arousal. Over the next weeks, torpor depth and duration decreased together with a reduction in resting metabolic rate at Ta 30–32°C. Our data show that development of endothermy and torpor expression in this altricial hamster is extremely fast. The results suggest that precocious torpor by juvenile hamsters in autumn and winter is an important survival tool in their vast and harsh Asian desert habitats, but likely also for many other small mammals and birds worldwide.

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]

Most mammals and birds are altricial, small and naked at birth/hatching. They attain endothermic thermoregulation at a fraction of their adult size at a vulnerable stage with high heat loss when many could profit from using torpor for energy conservation. Nevertheless, detailed data on the interrelations between torpor expression and development of endothermic thermoregulation are currently restricted to <0.1% of extant endotherms. We investigated at what age and body mass (BM) desert hamsters (Phodopus roborovskii), wild-caught in Inner Mongolia and born in autumn/early winter when environmental temperatures in the wild begin to decrease, are able to defend their body temperature (Tb) at an ambient temperature (Ta) of ∼21°C and how soon thereafter they could express torpor. Measurements of surface temperatures via infrared thermometer and thermal camera show that although neonate hamsters (BM 0.9 ± 0.1 g) cooled rapidly to near Ta, already on day 15 (BM 5.5 ± 0.2 g) they could defend a high and constant Tb. As soon as day 16 (BM 5.8 ± 0.2 g), when their maximum activity metabolism (measured as oxygen consumption) approached maxima measured in vertebrates, animals were able to enter torpor for several hours with a reduction of metabolism by >90%, followed by endothermic arousal. Over the next weeks, torpor depth and duration decreased together with a reduction in resting metabolic rate at Ta 30–32°C. Our data show that development of endothermy and torpor expression in this altricial hamster is extremely fast. The results suggest that precocious torpor by juvenile hamsters in autumn and winter is an important survival tool in their vast and harsh Asian desert habitats, but likely also for many other small mammals and birds worldwide. [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]

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).

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]

Herein, we compared the developmental maturity of the cranium, limbs, and feeding apparatus in a perinatal common vampire bat relative to its mother. In addition, we introduce a method for combining two computed tomographic imaging techniques to three-dimensionally reconstruct endocasts in poorly ossified crania. The Desmodus specimens were scanned using microcomputed tomography (microCT) and diffusible iodine-based contrast-enhanced CT to image bone and soft tissues. Muscles of the jaw and limbs, and the endocranial cavity were segmented using imaging software. Endocranial volume (ECV) of the perinatal Desmodus is 74% of adult ECV. The facial skeletal is less developed (e.g., palatal length 60% of adult length), but volumes for alveolar crypts/sockets of permanent teeth are nearly identical. The forelimb skeleton is uniformly less ossified than the distal hind limb, with no secondary centers ossified and an entirely cartilaginous carpus. All epiphyseal growth zones are active in the brachium and antebrachium, with the distal radius exhibiting the greatest number of proliferating chondrocytes arranged in columns. The hind limb skeleton is precociously ossified from the knee distally. The musculature of the fore limb, temporalis, and masseter muscles appear weakly developed (6-11% of the adult volume). In contrast, the leg and foot musculature is better developed (23-25% of adult volume), possibly enhancing the newborn's capability to grip the mother's fur. Desmodus is born relatively large, and our results suggest they are born neurally and dentally precocious, with generally underdeveloped limbs, especially the fore limb., (© 2023 American Association for Anatomy.)