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Cuticular hydrocarbons (CHCs) play an essential role in mate recognition in insects but the form and intensity of sexual selection on CHCs has only been evaluated in a handful of studies, and never in a natural population.We quantified sexual selection operating on CHCs in a wild population of sagebrush crickets, a species in which nuptial feeding by females imposes an unambiguous phenotypic marker on males. Multivariate selection analysis revealed a saddle-shaped fitness surface, suggesting a complex interplay between the total abundance of CHCs and specific CHC combinations in their influence on female choice. The fitness surface resulting from two axes of disruptive selection reflected a trade-off between short- and long-chained CHCs, suggesting that males may be sacrificing some level of desiccation resistance in favour of increased attractiveness. There was a significant correlation between male body size and total CHC abundance, suggesting that male CHCs provide females with a reliable cue for maximizing benefits obtained from males. Notwithstanding the conspicuousness of males� acoustic signals, our results suggest that selection imposed on males via female mating preferences may be far more complex than previously appreciated and operating in multiple sensory modalities. [ABSTRACT FROM AUTHOR]

In altricial birds, siblings raised within a nest usually leave the nest within hours of each other, despite often differing considerably in age. The youngest members of the brood are typically underdeveloped at this time and less likely than their older siblings to survive outside the nest, yet they risk abandonment if they do not fledge with their older siblings. Nest leaving is usually initiated by the older offspring, which may delay this process to provide more time for their younger siblings to mature, increasing the younger siblings' postfledging survival and their own inclusive fitness. We tested this hypothesis in a population of house wrens Troglodytes aedon and found that broods with broad age spans among siblings had longer nestling periods than broods with narrow age spans and that delayed fledging improves the survival and reproductive prospects of younger siblings, although at a potential cost to future siblings. We also manipulated age spans through cross-fostering and found that older foster nestlings postponed fledging when raised with younger broodmates, as predicted if the age of younger nestlings determines the time of fledging. Our results support kin-selection theory and demonstrate that the exact time of fledging is attributable, in part, to sib-sib interactions. [ABSTRACT FROM AUTHOR]

The Free Radical Theory of Ageing (FRTA) predicts that oxidative stress, induced when levels of reactive oxygen species exceed the capacity of antioxidant defenses, causes ageing. Recently, it has also been argued that oxidative damage may mediate important life-history trade-offs. Here, we use inbred lines of the decorated cricket, Gryllodes sigillatus, to estimate the genetic (co)variance between age-dependent reproductive effort, life span, ageing, oxidative damage, and total antioxidant capacity within and between the sexes. The FRTA predicts that oxidative damage should accumulate with age and negatively correlate with life span. We find that protein oxidation is greater in the shorter lived sex (females) and negatively genetically correlated with life span in both sexes. However, oxidative damage did not accumulate with age in either sex. Previously we have shown antagonistic pleiotropy between the genes for early-life reproductive effort and ageing rate in both sexes, although this was stronger in females. In females, we find that elevated fecundity early in life is associated with greater protein oxidation later in life, which is in turn positively correlated with the rate of ageing. Our results provide mixed support for the FRTA but suggest that oxidative stress may mediate sex-specific life-history strategies in G. sigillatus. [ABSTRACT FROM AUTHOR]

Females of many species obtain benefits by mating polyandrously, and often prefer novel males over previous mates. However, how do females recognise previous mates, particularly in the face of cognitive constraints? Female crickets appear to have evolved a simple but effective solution: females imbue males with their own cuticular hydrocarbons ( CHCs) at mating and utilise chemosensory self-referencing to recognise recent mates. Female CHC profiles exhibited significant additive genetic variation, demonstrating that genetically unique chemical cues are available to support chemosensory self-referencing. CHC profiles of males became more similar to those of females after mating, indicating physical transfer of CHCs between individuals during copulation. Experimental perfuming of males with female CHCs resulted in a female aversion to males bearing chemical cues similar to their own. Chemosensory self-referencing, therefore, could be a widespread mechanism by which females increase the diversity of their mating partners. [ABSTRACT FROM AUTHOR]

The article presents research which assessed the evidence for the heterozygote instability in house wrens microsatellite loci. The researchers analyzed 20 microsatellite loci of Troglodytes aedon also called as the songbird. They found the difference between the homologue and the allele affects the mutation rate of this species. The authors argue that instability in the bird's heterozygote is possible at microsatellite loci.

Although female multiple mating is ubiquitous in insects, its adaptive significance remains poorly understood. Benefits to multiple mating can accrue via direct material benefits, indirect genetic benefits, or both. We investigated the effects of multiple mating in the decorated cricket, Gryllodes sigillatus, by simultaneously varying the number of times that females mated and the number of different males with which they mated, measuring aspects of female fecundity and elements of offspring performance and viability. Multiple matings resulted in enhanced female fitness relative to single matings when females mated with different partners, but not when females mated repeatedly with the same male. Specifically, polyandrous females produced significantly more offspring surviving to reproductive maturity than did monogamous females mating once or mating repeatedly with the same male. These results suggest that the benefit females gain from multiple mating is influenced primarily by genetic and not material benefits. [ABSTRACT FROM AUTHOR]

Provides information on a study that showed that tests of the model derived for sperm lotteries can result in misleading inferences about the underlying mechanism of sperm precedence because the required inverse transformations may lead to a violation of fundamental assumptions of linear regression. Methodology of the study; Results and discussion on the study.

Measures lifetime polyandry of free-living female decorated crickets, Gryllodes sigillatus, in order to determine whether polyandry leads to an increase in offspring viability. Degree of polyandry exhibited by females; Comparison of the offspring reared by polyandrous females and those of monandrous females; Benefits from polyandry.

Female sagebrush crickets (Cyphoderris strepitans) feed on males' fleshy hind wings during copulation and ingest haemolymph oozing from the wounds they inflict. The wounds are not fatal and usually only a portion of the hind wings are eaten at any one mating, so that mated males are not precluded from mating again. However, based on their relative abundance in the population, virgin males have a higher mating success than non-virgin males. One explanation for this virgin-male mating advantage is that non-virgin males, having been depleted of their energy reserves through the wing-feeding behaviour of their mates, are unable to sustain the same level of acoustic signalling they produce prior to copulation. Previous assays of male signalling behaviour have provided some support to this hypothesis. However, an alternative explanation is that females actively seek out virgin males as mates because of the greater material resources they offer. If the acoustic structure of males' signals were systematically altered by the loss of hind-wing material underlying the sound-producing tegmina, females could potentially discriminate against mated males through reduced phonotaxis to their calls. We tested this hypothesis by experimentally removing one hind wing from virgin males, thereby simulating the non-virgin condition without the attendant costs of copulation. We compared the mating success of these 'asymmetrical' males with that of sham-operated virgin males when competing under natural conditions. In a companion laboratory study, we used time-lapse video recording to examine the possibility that female preferences are exerted only after pair formation has occurred. There was no significant difference in male mating success across treatments in either study. We conclude, therefore, that the virgin-male mating advantage does not stem from an acoustically mediated, non-independent female mating preference, but rather, from the differential competitiveness of males. [ABSTRACT FROM AUTHOR]

Focuses on the importance of the manipulation of ejaculates to sexual selection in animals. Testing of the hypothesis on removal of the externally attached spermatophore in crickets; What it gives the female as means of postcopulatory mate choice; How the tests were conducted; Discussion of female control of sperm transfer and intraspecific variation in sperm precedence.

Focuses on the effect of widow in the reproduction of burying beetles. Assessment paternity of the offspring; Rarity of paternal care; Completion of larval development.

Theoretically, males should increase their ejaculate expenditure when the probability of sperm competition occurring (or risk) is high but decrease ejaculate expenditure as the number of competing ejaculates (or intensity) increases. Here we examine whether male decorated crickets (Gryllodes sigillatus) use cuticular hydrocarbons (CHCs) transferred to females by rival males at mating to assess the risk and intensity of sperm competition and adjust their ejaculate accordingly. Unmated females and those perfumed with CHCs extracted from one, three, or five males could be distinguished chemically, providing a reliable cue of the risk and intensity of sperm competition. In agreement with theory, males mating with these females increased sperm number with the risk of sperm competition and decreased sperm number with the intensity of sperm competition. Similarly, as the risk of sperm competition increased, males produced a larger and more attractive spermatophylax (an important non-sperm component of the ejaculate) but these traits did not vary with the intensity of sperm competition. Our results therefore demonstrate that both sperm and non-sperm components of the male ejaculate respond to the risk and intensity of sperm competition in different ways and that CHCs provide males with an important cue to strategically tailor their ejaculate. [ABSTRACT FROM AUTHOR]

The evolution of nuptial gifts has traditionally been considered a harmonious affair, providing benefits to both mating partners. There is growing evidence, however, that receiving a nuptial gift can be actively detrimental to the female. In decorated crickets (Gryllodes sigillatus), males produce a gelatinous spermatophylax that enhances sperm transfer but provides little nutritional benefit and hinders female post-copulatory mate choice. Here, we examine the sexually antagonistic coevolution of the spermatophylax and the female feeding response to this gift in G. sigillatus maintained in experimental populations with either a male-biased or female-biased adult sex ratio. After 25 generations, males evolving in male-biased populations produced heavier spermatophylaxes with a more manipulative combination of free amino acids than those evolving in female-biased populations. Moreover, when the spermatophylax originated from the same selection regime, females evolving in male-biased populations always had shorter feeding durations than those evolving in female-biased populations, indicating the evolution of greater resistance. Across populations, female feeding duration increased with the mass and manipulative combination of free amino acids in the spermatophylax, suggesting sexually antagonistic coevolution. Collectively, our work demonstrates a key role for interlocus sexual conflict and sexually antagonistic coevolution in the mating system of G. sigillatus. [ABSTRACT FROM AUTHOR]

Bird song is a classic example of a sexually selected trait, but much of the work relating individual song components to fitness has not accounted for song typically being composed of multiple, often-correlated components, necessitating a multivariate approach. We explored the role of sexual selection in shaping the complex male song of house wrens (Troglodytes aedon) by simultaneously relating its multiple components to fitness using multivariate selection analysis, which is widely used in insect and anuran studies but not in birds. The analysis revealed significant variation in the form and strength of selection acting on song across different selection episodes, from nest-site defense to recruitment of offspring to the breeding population. Males that sang more song typically employed in close communication sired more offspring that were subsequently recruited to the breeding population than those that sang more far-communication song. However, this relationship was not consistent across earlier selection episodes, as evidenced by non-linear selection acting on these song components in other contexts. Collectively, our results present a complex picture of multivariate selection on male song structure that would not be evident using univariate approaches and suggest possible trade-offs within and among song components at different points of the breeding season. [ABSTRACT FROM AUTHOR]

Background: Immature stages of many animals can forage and feed on their own, whereas others depend on their parents’ assistance to obtain or process food. But how does such dependency evolve, and which offspring and parental traits are involved? Burying beetles (Nicrophorus) provide extensive biparental care, including food provisioning to their offspring. Interestingly, there is substantial variation in the reliance of offspring on post-hatching care among species. Here, we examine the proximate mechanisms underlying offspring dependence, focusing on the larvae of N. orbicollis, which are not able to survive in the absence of parents. We specifically asked whether the high offspring dependence is caused by (1) a low starvation tolerance, (2) a low ability to self-feed or (3) the need to obtain parental oral fluids. Finally, we determined how much care (i.e. duration of care) they require to be able to survive. Results: We demonstrate that N. orbicollis larvae are not characterized by a lower starvation tolerance than larvae of the more independent species. Hatchlings of N. orbicollis are generally able to self-feed, but the efficiency depends on the kind of food presented and differs from the more independent species. Further, we show that even when providing highly dependent N. orbicollis larvae with easy ingestible liquefied mice carrion, only few of them survived to pupation. However, adding parental oral fluids significantly increased their survival rate. Finally, we demonstrate that survival and growth of dependent N. orbicollis larvae is increased greatly by only a few hours of parental care. Conclusions: Considering the fact that larvae of other burying beetle species are able to survive in the absence of care, the high dependence of N. orbicollis larvae is puzzling. Even though they have not lost the ability to self-feed, an easily digestible, liquefied carrion meal is not sufficient to ensure their survival. However, our results indicate that the transfer of parental oral fluids is an essential component of care. In the majority of mammals, offspring rely on the exchange of fluids (i.e. milk) to survive, and our findings suggest that even in subsocial insects, such as burying beetles, parental fluids can significantly affect offspring survival. [ABSTRACT FROM AUTHOR]

Dietary macronutrients regulate life span and aging, yet little is known about their evolutionary effects. Here, we examine the evolutionary response of these traits in decorated crickets (Gryllodes sigillatus) maintained on diets varying in caloric content and protein-to-carbohydrate ratio. After 37 generations, each population was split: half remained on the evolution diet, and half switched to a standardized diet. Crickets lived longer and aged slower when evolving on high-calorie (both sexes) and carbohydrate-biased (females only) diets and had lower baseline mortality on high-calorie (females only) diets. However, on the standardized diet, crickets lived longer when evolving on high-calorie diets (both sexes), aged slower on high-calorie (females only) and carbohydrate-biased (both sexes) diets, and had lower baseline mortality on high-calorie (males only) and protein-biased (both sexes) diets. Life span was longer, and baseline mortality was lower when provided with the evolution vs. the standardized diet, but the aging rate was comparable. Moreover, life span was longer, aging slower (females only), and baseline mortality was lower (males only) compared to our evolved baseline, suggesting varying degrees of dietary adaptation. Collectively, we show dietary components influence the evolution of life span and aging in different ways and highlight the value of combining experimental evolution with nutritional geometry. [ABSTRACT FROM AUTHOR]

The operational sex ratio (OSR) is a key component influencing the magnitude of sexual selection driving the evolution of male sexual traits, but males often also retain the ability to plastically modulate trait expression depending on the current environment. Here we employed an experimental evolution approach to determine whether the OSR affects the evolution of male calling effort in decorated crickets, a costly sexual trait, and whether plasticity in calling effort is altered by the OSR under which males have evolved. Calling effort of males from 2 selection regimes maintained at different OSRs over 18–20 generations (male vs. female biased) was recorded at 2 different levels of perceived competition, in the absence of rivals or in the presence of an experimentally muted competitor. The effect of the OSR on the evolution of male calling effort was modest, and in the opposite direction predicted by theory. Instead, the immediate competitive environment strongly influenced male calling effort as males called more in the presence of a rival, revealing considerable plasticity in this trait. This increased calling effort came at a cost, however, as males confined with a muted rival experienced significantly higher mortality. [ABSTRACT FROM AUTHOR]

Male sagebrush crickets (Cyphoderris strepitans) permit females to engage in an unusual form of sexual cannibalism during copulation: females feed on males' fleshy hind wings and ingest hemolymph oozing from the wounds they inflict. These wounds are not fatal, and normally only a portion of the hind wings are eaten at any one mating, so that mated males are not precluded from mating again. As a result, nonvirgin males have fewer marital resources to offer females than do virginmales, such that females should be selected to preferentially mate with high-investment virgin males. We tested the hypothesis that female mating preferences favor males capable of supplying females with the highest material investment. Our results indicate that both female diet and opportunities for sexual cannibalism influence female matingbehavior. Females maintained on a low-nutrient diet mounted males significantly sooner than females maintained on a high-nutrient diet, indicating that a female's overall nutrient intake may determine her propensity to mate. In addition, females were significantly more reluctant to mount and mate with males whose hind wings had been surgically removed and thus were incapable of providing females with a wing meal. Finally, females initially mated to dewinged males remated with winged males significantly sooner than females allowed to feed freely during their initial mating, resulting in cryptic female choice of investing males. [ABSTRACT FROM AUTHOR]

Accessory gland proteins contained within male ejaculates influence female reproduction and survival in insects. Nuptial food gifts offered by male crickets and katydids, the consumption of which may also alter female behaviour and physiology after mating, also contain accessory gland proteins. However, because nuptial feeding promotes the transfer of sperm and ejaculatory substances, it is unclear whether it is accessory gland proteins in the ejaculate, nuptial gifts or both that mediate these effects. Here we evaluate the effects of mating, nuptial gifts and accessory gland proteins on female reproduction in a gift-giving cricket (Gryllodes sigillatus) using a crossed experimental design. We injected females of varying mating experience with male accessory gland extract, permitting some females to consume the nuptial food gift, while experimentally preventing others from doing so. Mating resulted in a significant decrease in female sexual receptivity, an effect likely mediated by accessory gland proteins contained in the male's ejaculate. Consumption of the nuptial food gift resulted in the premature cessation of nuptial feeding following the female's next mating, leading to a concomitant decrease in sperm transfer by a rival male. This is a novel finding, demonstrating that fitness benefits to males of nuptial gift provisioning can also accrue over later copulations by their mates. Neither injection of accessory gland extract nor nuptial feeding influenced female oviposition; the absence of any effect of the injection of accessory gland proteins on female reproduction suggests that their efficacy may depend on their direct introduction into the female reproductive tract. More research is required to identify the specific accessory gland proteins in ejaculates and nuptial gifts that modulate female behaviour and physiology, potentially illuminating the evolution of these mechanistic tactics underlying sexual conflict. • How do accessory gland proteins affect female reproduction in crickets? • Mating resulted in a decrease in female sexual receptivity. • Nuptial feeding in one mating influenced time spent feeding in the next. • Thus, food gifts influence sperm transfer in both current and future copulations. • Neither injection of accessory gland extract nor nuptial gifts affected egg laying. [ABSTRACT FROM AUTHOR]

Despite decades of focus on crickets (family: Gryllidae) as a popular commodity and model organism, we still know very little about their immune responses to microbial pathogens. Previous studies have measured downstream immune effects (e.g., encapsulation response, circulating hemocytes) following an immune challenge in crickets, but almost none have identified and quantified the expression of immune genes during an active pathogenic infection. Furthermore, the prevalence of covert (i.e., asymptomatic) infections within insect populations is becoming increasingly apparent, yet we do not fully understand the mechanisms that maintain low viral loads. In the present study, we measured the expression of several genes across multiple immune pathways in Gryllodes sigillatus crickets with an overt or covert infection of cricket iridovirus (CrIV). Crickets with overt infections had higher relative expression of key pathway component genes across the Toll, Imd, Jak/STAT, and RNAi pathways. These results suggests that crickets can tolerate low viral infections but can mount a robust immune response during an overt CrIV infection. Moreover, this study provides insight into the immune strategy of crickets following viral infection and will aid future studies looking to quantify immune investment and improve resistance to pathogens. [ABSTRACT FROM AUTHOR]

Male Nicrophorus burying beetles utilize two alternative mate-finding tactics: searching and signalling. The searching tactic involves flying in search of a carcass on which to mate, while the signalling tactic involves emitting pheromone in the absence of a carcass to attract females. All males use both tactics, but the amount of time spent using each tactic differs between individuals. Because all males are phenotypically plastic in the time spent using alternative behaviours, the expression is likely to be condition dependent on some environmental cue, such as the availability of reproductive resources (i.e. females and carcasses). We tested how the expression of alternative tactics is influenced by previous mating experience and the perceived availability of females versus carcasses by using a repeated measures design in which mate-finding behaviour of males was observed before and after exposure to: (1) multiple females but no carcasses, (2) multiple females and multiple carcasses, (3) multiple carcasses but no females, or (4) no females or carcasses (control). Males in the multiple-female group (but lacking a carcass) allocated significantly more time to signalling, as did males in the control group lacking both mating and carcass experience. Thus, males that did not encounter carcasses during the treatment period increased pheromone emission thereafter. In the two groups that were given carcasses, however, investment in signalling was not altered. With respect to time allocated to searching, control, multiple-female and multiple-carcass groups all significantly decreased time spent searching, whereas males in the female-and-carcass group did not alter time allocated to searching. Our results demonstrate that environmental cues do influence which alternative tactic male burying beetles use, and that the chosen tactic is influenced by the availability of both receptive females and carcasses on which to breed. [ABSTRACT FROM AUTHOR]

Despite classical expectations of a trade-off between immune activity and reproduction, an emergent view suggests that individuals experiencing activation of their immune system actually increase reproductive effort and allocation to offspring as a form of terminal investment in response to reduced survival probability. However, the components and mechanisms of increased parental investment following immunostimulation are currently unknown. We hypothesize that increased glucocorticoid production following immunostimulation modulates the increase in reproductive effort that constitutes terminal investment. We activated the immune system of breeding female house wrens (Troglodytes aedon) with an immunogen and cross-fostered the eggs that they subsequently produced to separate prenatal and postnatal components of maternal investment. Cross-fostering revealed an increase in both pre- and postnatal allocation from immunostimulated females, which was confirmed by quantification of egg constituents and maternal provisioning behavior. The increase in maternal provisioning was mediated, at least in part, by increased corticosterone in these females. Offspring immune responsiveness was also enhanced through transgenerational immune priming via the egg. Thus, our results indicate that maternal immunostimulation induces transgenerational effects on offspring through both pre- and postnatal parental effects and support an important role for corticosterone in mediating parental investment. [ABSTRACT FROM AUTHOR]

A major component of sex-allocation theory, the Trivers-Willard model ( TWM), posits that sons and daughters are differentially affected by variation in the rearing environment. In many species, the amount of parental care received is expected to have differing effects on the fitness of males and females. When this occurs, the TWM predicts that selection should favour adjustment of the offspring sex ratio in relation to the expected fitness return from offspring. However, evidence for sex-by-environment effects is mixed, and little is known about the adaptive significance of producing either sex., Here, we test whether offspring sex ratios vary according to predictions of the TWM in the house wren ( Troglodytes aedon, Vieillot). We also test the assumption of a sex-by-environment effect on offspring using two experiments, one in which we manipulated age differences among nestlings within broods, and another in which we held nestling age constant but manipulated brood size., As predicted, females with high investment ability overproduced sons relative to those with lower ability. Males were also overproduced early within breeding seasons. In our experiments, the body mass of sons was more strongly affected by the sibling-competitive environment and resource availability than that of daughters: males grew heavier than females when reared in good conditions but were lighter than females when in poor conditions., Parents rearing broods with 1:1 sex ratios were more productive than parents rearing broods biased more strongly towards sons or daughters, suggesting that selection favours the production of mixed-sex broods. However, differences in the condition of offspring as neonates persisted to adulthood, and their reproductive success as adults varied with the body mass of sons, but not daughters, prior to independence from parental care. Thus, selection should favour slight but predictable variations in the sex ratio in relation to the quality of offspring that parents are able to produce., Offspring sex interacts with the neonatal environment to influence offspring fitness, thus favouring sex-ratio adjustment by parents. However, increased sensitivity of males to environmental conditions, such as sibling rivalry and resource availability, reduces the fitness returns from highly male-biased broods. [ABSTRACT FROM AUTHOR]

Although dietary macronutrients are known to regulate insect immunity, few studies have examined their evolutionary effects. Here, we evaluate this relationship in the cricket Gryllodes sigillatus by maintaining replicate populations on four diets differing in protein (P) to carbohydrate (C) ratio (P‐ or C‐biased) and nutritional content (low‐ or high‐nutrition) for >37 generations. We split each population into two; one maintained on their evolution diet and the other switched to their ancestral diet. We also maintained populations exclusively on the ancestral diet (baseline). After three generations, we measured three immune parameters in males and females from each population. Immunity was higher on P‐biased than C‐biased diets and on low‐ versus high‐nutrition diets, although the latter was most likely driven by compensatory feeding. These patterns persisted in populations switched to their ancestral diet, indicating genetic divergence. Crickets evolving on C‐biased diets had lower immunity than the baseline, whereas their P‐biased counterparts had similar or higher immunity than the baseline, indicating that populations evolved with dietary manipulation. Although females exhibited superior immunity for all assays, the sexes showed similar immune changes across diets. Our work highlights the important role that macronutrient intake plays in the evolution of immunity in the sexes. [ABSTRACT FROM AUTHOR]

Avian eggshell pigmentation may provide information about a female's physiological condition, in particular her state of oxidative balance. Previously we found that female House Wrens (Troglodytes aedon Vieillot, 1809) with lighter, less-maculated, and redder ground-colored shells were older and produced heavier offspring than females laying more-maculated and browner eggs. The strong pro-oxidant protoporphyrin is responsible for this species' eggshell pigmentation, so differences in pigmentary coloration may be related to eggshell protoporphyrin content and reflect female oxidative balance and condition during egg formation. Therefore, we tested the assumption that egg-surface coloration is related to the amount of protoporphyrin in the shell matrix. We analyzed digital photographs of eggs to determine maculation coverage as a measure of the overall ground coloration of the egg and its red-, green-, and blue-channel pixel values. Pigments were then extracted from these same eggs and analyzed using high-performance liquid chromatography. There was a strong, positive relationship between eggshell redness and protoporphyrin content of eggshells, but no relationship between percent maculation and protoporphyrin content. Thus, when older, larger females deposit more protoporphyrin in their eggshells, this may reflect a tolerance for high levels of circulating protoporphyrin or an effective mechanism for off-loading protoporphyrin into the eggshell matrix. [ABSTRACT FROM AUTHOR]

In addition to food and protection, altricial young in many species are ectothermic and require that endothermic parents provide warmth to foster growth, yet only one parent—typically the female—broods these young to keep them warm. When this occurs, reduced provisioning by males obliges females to forage instead of providing warmth for offspring, favoring the temporal mapping of male activities. We assessed this in a wild house wren population while experimentally feeding nestlings to control offspring satiety. While brooding, females look out from the nest to inspect their surroundings, and we hypothesized that this helps to determine if their mate is nearby and likely to deliver food to the brood (males pass food to brooding females, which pass the food to nestlings). Females looked out from the nest less often when their partner was singing nearby and when his singing and provisioning were temporally linked, signaling his impending food delivery. Females also left to forage less often when their mate was nearby and likely to deliver food. Nestling begging did not affect these behaviors. Females looking out from the nest more often also provisioned at a higher rate and were more likely to divorce and find a new mate prior to nesting again within seasons, as expected if females switch mates when a male fails to meet expectations. Our results suggest anticipatory effects generated by male behavior and that brooding females temporally map male activity to inform decisions about whether to continue brooding or to leave the nest to forage. [ABSTRACT FROM AUTHOR]

The dynamic terminal investment threshold model posits that the propensity of an individual to terminally invest in response to an immediate survival threat, such as an infection, depends on other factors that alter an individual's residual reproductive value. Here, we explore the potential for dynamic terminal investment in burying beetles, insects that inter small vertebrate carcasses as the sole source of food for their offspring and that exhibit extensive biparental care. We injected males at two different ages with heat-killed bacteria and measured their reproductive output, predicting that immune-challenged males would show a longer period of parental care, consume less of the carcass and produce a greater number of larvae in the current reproductive attempt compared with control males. We further predicted that terminal investment would be more evident in older males than in younger ones. Males challenged with heat-killed bacteria as virgins prior to their first reproductive attempt showed no evidence of terminal investment, whereas these same individuals when challenged at a later age as reproductively experienced breeders in a subsequent reproductive attempt showed increased reproductive output. Older, immune-challenged individuals gained less mass during the time on the carcass than control males, suggesting that this terminal investment was subsidized, at least in part, by males refraining from eating as much of the carcass as they might have otherwise done in the absence of an immune challenge, leaving more carrion for their offspring to consume at the expense of their own maintenance and future reproduction. Because it seems likely than an individual's residual reproductive value decreases with both increasing age and reproductive experience, the context-specific terminal investment shown by immune-challenged males in the current study aligns with theory. • Older male burying beetles terminally invest, but younger males do not. • Older immune-challenged males produced more young than control males. • Older immune-challenged males consumed less of the carcass than control males. • Terminal investment was thus subsidized by older males forgoing feeding. • These results align with the dynamic terminal investment threshold model. [ABSTRACT FROM AUTHOR]

Corticosterone is the primary metabolic steroid in birds and is vital for maintaining homeostasis. However, the relationship between baseline corticosterone and reproduction is unclear, and we lack an understanding of how differences in baseline corticosterone at one stage of the breeding cycle influence reproductive effort at later stages. In a wild population of house wrens, we quantified the concentration of corticosterone in yolks of freshly laid eggs as an integrated measure of maternal physiology and related this to a behavioral measure of stress reactivity made during the nestling period, namely, the latency with which females resumed parental activities following a standardized disturbance at their nest (setting up a camera to record provisioning). Females that recently produced eggs containing higher corticosterone concentrations, which were significantly repeatable within females, took longer to resume activity related to parental care (i.e., feeding and brooding young) following the disturbance. Moreover, a female’s latency to resume parental activities negatively predicted her provisioning of nestlings with food and the condition of these young at fledging but did not predict the number fledged. We cross-fostered offspring prior to hatching so these effects on maternal behavior are independent of any prenatal maternal effects on nestlings via the egg. These results are consistent with earlier findings, suggesting that females with higher baseline corticosterone during egg laying or early incubation tend to prioritize self-maintenance over reproduction compared with females with lower baseline corticosterone and suggest that a female’s latency to return to her nest and resume parental care following a disturbance might represent a simple, functional measure of maternal stress reactivity. [ABSTRACT FROM AUTHOR]

The coevolution of parental supply and offspring demand has long been thought to involve offspring need driving begging and parental care, leaving other hypotheses underexplored. In a population of wild birds, we experimentally tested whether begging serves as a negatively condition-dependent signal of need or a positively condition-dependent signal of quality. Across multiple years, we supplemented nestling house wrens with food shortly after hatching and simultaneously manipulated corticosterone levels to simulate the hunger-induced increase in glucocorticoids thought to mediate begging. This allowed us to also test whether begging is simply a proximate signal of hunger. Days after supplementation ended, food-supplemented nestlings were in better condition than nonsupplemented nestlings and begged for food at an increased rate; their parents, in turn, increased provisioning to a greater extent than parents of nonsupplemented young, as begging positively predicted provisioning. Food-supplemented nestlings therefore attained above-average condition, which predicted their recruitment as breeding adults in the local population. Glucocorticoids increased begging in the short term, but this transient effect depended on satiety. Thus, glucocorticoids promoted begging as a proximate response to hunger, whereas the longer-term changes in nestling condition, begging, and food provisioning suggest that begging ultimately signals offspring quality to elicit increased investment, thereby enhancing offspring survival. [ABSTRACT FROM AUTHOR]

1. Corticosterone plays a central role in maintaining homeostasis, promoting energy acquisition, and regulating the stress response in birds. Exposure to elevated levels of corticosterone during development can profoundly alter offspring behaviour and physiology, but the effects of elevated maternal corticosterone on offspring development remain poorly understood. 2. We tested two competing hypotheses concerning the effect of maternally derived corticosterone on growth and development of free-living house wrens: (i) elevated maternal corticosterone causes damaging effects on nestling phenotype and fitness (collateral damage hypothesis) and (ii) increased maternal corticosterone enhances offspring fitness by preparing nestlings for the environment experienced by their mother (environmental/maternal-matching hypothesis). 3. We used a non-invasive means to increase maternal corticosterone by providing females with corticosterone-injected mealworms prior to and during egg production in the absence of any overt pre-natal maternal stress. To disentangle pre- and post-natal effects of this elevation in maternal corticosterone, we cross-fostered young in two experiments: (i) nestlings of control and experimental females were reared by unmanipulated, natural females in a uniform maternal environment; (ii) a split-brood design that enabled us to assess the interaction between the mother's corticosterone treatment and that of the nestlings. 4. There were significant pre-natal effects of increased maternal corticosterone on nestling growth and survival. Offspring of females experiencing experimentally increased corticosterone were heavier and larger than offspring of control females. There also was a significant interaction between maternal corticosterone treatment and the corticosterone treatment to which young were exposed within the egg in their effect on nestling survival while in the nest; experimental young exhibited greater survival than control young, but only when reared by control mothers. There was also a significant effect of maternal corticosterone treatment on nestling stress reactivity and, in both experiments, on the eventual recruitment of offspring as breeding adults in the local population. 5. These patterns are broadly consistent with the environmental/maternal-matching hypothesis, and highlight the importance of disentangling pre- and post-natal effects of manipulations of maternal hormone levels on offspring phenotype. [ABSTRACT FROM AUTHOR]

Life-history theory assumes that traits compete for limited resources, resulting in trade-offs. The most commonly manipulated resource in empirical studies is the quantity or quality of diet. Recent studies using the geometric framework for nutrition, however, suggest that trade-offs are often regulated by the intake of specific nutrients, but a formal approach to identify and quantify the strength of such trade-offs is lacking. We posit that trade-offs occur whenever life-history traits are maximized in different regions of nutrient space, as evidenced by nonoverlapping 95% confidence regions of the global maximum for each trait and large angles (v) between linear nutritional vectors and Euclidean distances (d) between global maxima. We then examined the effects of protein and carbohydrate intake on the tradeoff between reproduction and aspects of immune function inmale and female Gryllodes sigillatus. Female encapsulation ability and egg production increased with the intake of both nutrients, whereas male encapsulation ability increased with protein intake but calling effort increased with carbohydrate intake. The trade-offs between traits was therefore larger in males than in females, as demonstrated by significant negative correlations between the traits in males, nonoverlapping 95% confidence regions, and larger estimates of v and d. Under dietary choice, the sexes had similar regulated intakes, but neither optimally regulated nutrient intake for maximal trait expression. We highlight the fact that greater consideration of specific nutrient intake is needed when examining nutrient space-based trade-offs. [ABSTRACT FROM AUTHOR]

Abstract: The terminal investment hypothesis proposes that decreased expectation of future reproduction (e.g., arising from a threat to survival) should precipitate increased investment in current reproduction. The level at which a cue of decreased survival is sufficient to trigger terminal investment (i.e., the terminal investment threshold) may vary according to other factors that influence expectation for future reproduction. We test whether the terminal investment threshold varies with age in male crickets, using heat‐killed bacteria to simulate an immune‐inducing infection. We measured calling effort (a behavior essential for mating) and hemolymph antimicrobial activity in young and old males across a gradient of increasing infection cue intensity. There was a significant interaction between the infection cue and age in their effect on calling effort, confirming the existence of a dynamic terminal investment threshold: young males reduced effort at all infection levels, whereas old males increased effort at the highest levels relative to naïve individuals. A lack of a corresponding decrease in antibacterial activity suggests that altered reproductive effort is not traded against investment in this component of immunity. Collectively, these results support the existence of a dynamic terminal investment threshold, perhaps accounting for some of the conflicting evidence in support of terminal investment. [ABSTRACT FROM AUTHOR]

In animal species in which parents provide food to their dependent young, offspring often display conspicuous begging signals. These solicitation behaviors are important components of parent-offspring communication, but it is currently unclear how they and the parental response covary with offspring dependency on parental food provisioning across species. Burying beetles (Nicrophorus) are well known for providing elaborate biparental care, including provisioning of begging larvae. By using a multispecies approach, we show that larval begging intensity, as well as the time parents spend provisioning, differ greatly between individuals of the 3 species: N. orbicollis, N. pustulatus, and N. vespilloides. Our results demonstrate that the most dependent offspring of N. orbicollis invest the most time in begging, whereas the most independent offspring of N. pustulatus invest the least amount of time in begging. Thus, we suggest that begging intensity differs due to intrinsic differences in nutritional need between the species rather than because of an arbitrary divergence in begging behavior. We further show that in all 3 species, females spend significantly more time provisioning than males, although there is considerable divergence between species in the extent to which females and males contribute to the provisioning of larvae. We discuss the potential selective factors leading to this diversification of offspring begging and parental provisioning in relation to the distinct variation in offspring dependence between the 3 species. [ABSTRACT FROM AUTHOR]