Females In Better Body Condition Research Articles

Variation in nuptial color in relation to sex, individual quality and mating success in the sex-role reversed Phalaropus fulicarius (Red Phalarope)

Abstract In most bird species, males are more ornamented and compete for females, who contribute more to offspring care. In a minority of species this pattern is reversed, with more colorful females competing for mates and males taking care of parental duties. In such sex-role reversed species, the links between colorful ornamentation, individual quality and mating success are not well established. Phalaropus fulicarius (Red Phalarope) is a colorful sex-role reversed migratory shorebird with regular social polyandry, in which both sexes show considerable color variation. Here, we describe sex differences in color and quantify associations between color variation and indicators of quality and mating success in both sexes. Using a large sample of photos collected across three consecutive years on the Arctic breeding grounds, we scored color variation for four body parts (bill, crown, cheek and breast), and analyzed scores separately and combined into an overall color score. Females were more colorful and larger than males, and individuals could be unambiguously sexed by crown color. Nevertheless, there was substantial variation within sexes and some overlap between males and females in bill, cheek, breast, and overall color scores. Assortative mating by color was only found for the bill. Color variation did not correlate with plasma testosterone levels, except for male cheek color. Females in better body condition had yellower bills and higher overall color scores, while early-arriving birds had higher breast and overall scores. Phalaropus fulicarius that bred locally were heavier than those that did not, but they did not have higher color scores. Female color variation did not predict the probability of local social polyandry nor variation in clutch size, and male coloration did not predict the probability of nest predation. In conclusion, P. fulicarius color variation showed modest correlations with individual quality and was unrelated to variation in local reproductive success.

Climate and non‐native herbivores influence reproductive investment by Greater Sage‐grouse

AbstractHighly seasonal environments can increase competition among herbivores for nutrients, affecting rates of reproduction and survival. There is concern about the impacts of non‐native ungulates on Greater Sage‐grouse in the Great Basin of North America. We estimated nesting propensity, the annual proportion of females attempting a nest, for Greater Sage‐grouse in relation to the abundance of ungulates using 7 years of data from the northwestern Great Basin, USA. We focused on nesting because it is the necessary first major investment required for the production of new recruits. We used a Bayesian multistratum model to investigate the effects of weather and sympatric non‐native herbivores, free‐roaming horses and domestic cattle, on reproductive rates and female survival of adult and yearling sage‐grouse. Adults nested at a higher rate (0.931, 95% CI, 0.904–0.953) than yearlings (0.867, 95% CI, 0.802–0.922) under average conditions of covariates other than age. If the first nest failed, renesting rates were similar between adults (0.349, 95% CI, 0.292–0.410) and yearlings (0.353, 95% CI, 0.217–0.507). Females in better body condition at the start of the season nested at higher rates, and moderately snowy winters led to the highest nesting propensity during the following spring. Drier conditions led to low rates of nesting, particularly in areas with dense cattle grazing. Female survival was lower for nesting females, indicating a survival cost of reproduction. Areas with abundant free‐roaming horses had slightly higher nesting propensity, though other research suggests negative impacts later in the breeding cycle. Sage‐grouse face life history trade‐offs that may be shifting due to changing climatic conditions. Our work suggests that the effects of competition with non‐native ungulates on sage‐grouse life histories may be exacerbated by adverse weather.

Long‐term increase in female body condition and its effect on reproduction in two European red‐listed species, Common Pochard (Aythya ferina) and Tufted Duck (Aythya fuligula)

Body condition of breeding females is an important driver of an individual's fitness and the consequent dynamics of populations. Long‐term changes in female body condition are likely to be affected by recent shifts in climatic and environmental conditions that can result in changes to population demography. To help explain the drivers shaping body condition during the incubation period and its consequences for reproductive success, we examined the long‐term pattern in the body condition of breeding females of two declining sympatric diving duck species: Common Pochard Aythya ferina and Tufted Duck Aythya fuligula. We analysed the data obtained from 139 females of Common Pochard and 251 females of Tufted Duck breeding on fishponds in South Bohemia, Czechia, between 2004 and 2020. We calculated the body condition index of females during late incubation based on the residuals from the relationship between body mass and tarsus length and used the incubation stage as an additional predictor of body mass. Body condition of both species did not decline over the 17 years of the study. The effect of winter weather conditions (winter temperature), water transparency (a proxy for food availability) and reproductive investment on body condition was not confirmed. Female body condition positively affected mean egg mass and hatchability in both studied species, i.e. females in better body condition laid larger eggs and hatched eggs with a higher hatching probability. We conclude that the population declines of the studied species are probably not connected to decreasing body condition of breeding females, but other reasons such as change in breeding propensity or offspring survival and recruitment should be considered in future studies.

Drivers of within- and among-individual variation in risk-taking behaviour during reproduction in a long-lived bird.

Plastic and selective mechanisms govern parental investment adjustments to predation threat. We investigated the relative importance of plasticity and selection in risk-taking propensity of incubating female common eiders Somateria mollissima facing unprecedented predation in SW Finland, Baltic Sea. Using a 12-year individual-based dataset, we examined within- and among-individual variation in flight initiation distance (FID), in relation to predation risk, nest detectability, individual traits and reproductive investment (NFID = 1009; Nindividual = 559). We expected females nesting in riskier environments (higher predation risk, lower nest concealment) to mitigate environmentally imposed risk by exhibiting longer FIDs, and females investing more in current reproduction (older, in better condition or laying larger clutches) to display shorter FIDs. The target of predation-adult or offspring-affected the mechanisms adapting risk-taking propensity; females plastically increased their FID under higher adult predation risk, while risk-avoiding breeders were predominant on islands with higher nest predation risk. Risk-taking females selected thicker nest cover, consistent with personality-matching habitat choice. Females plastically attenuated their anti-predator response (shorter FIDs) with advancing age, and females in better body condition were more risk-taking, a result explained by selection processes. Future research should consider predator type when investigating the fitness consequences of risk-taking strategies.

Differential allocation in a gift-giving spider: males adjust their reproductive investment in response to female condition

BackgroundWhen males are selective, they can either reject low-quality females or adjust their reproductive investment in response to traits that indicate female quality (e.g., body size or condition). According to the differential allocation hypothesis, males increase their reproductive investment when paired with high-quality females (positive differential allocation) or increase their reproductive investment when paired with low-quality females (negative differential allocation). This hypothesis has been proposed for monogamous species with biparental care, and most empirical studies focus on birds. Here we used the polygamous spider Paratrechalea ornata, in which males offer prey wrapped in silk as nuptial gifts, to test whether males adjust their reproductive investment in gift size, pre-copulatory and copulatory courtship, and sperm transfer in response to female body condition.ResultsMales exposed to females in good body condition added more flies to the gift, stimulated these females longer with abdominal touches during pre-copulatory courtship, and had longer pedipalp insertions than males exposed to females in poor body condition. Female condition affected neither silk investment in nuptial gift wrapping nor the quantity of sperm transferred by males. Finally, females in good body condition oviposited faster after copulation and laid more eggs than females in poor body condition.ConclusionsWe provide experimental evidence that males of a gift-giving spider exhibit positive differential allocation in three key aspects of their reproductive investment: the size of the nutritious gift, duration of pre-copulatory courtship, and duration of pedipalp insertions, which is regarded as a form of copulatory courtship in spiders. This positive differential allocation is likely associated with the benefits of copulating with females in good body condition. These females are more fecund and oviposit faster after copulation than females in poor body condition, which under natural field conditions probably reduces the risk of multiple matings and thus the level of sperm competition faced by the males. As a final remark, our findings indicate that the hypothesis of differential allocation also applies to species with a scramble competition mating system, in which males heavily invest in nuptial gift construction, but not in parental care.

Glucocorticoids, state-dependent reproductive investment and success in the face of danger in a long-lived bird

Glucocorticoid hormones may mediate trade-offs between current and future reproduction. However, understanding their role is complicated by predation risk, which simultaneously affects the value of the current reproductive investment and elevates glucocorticoid levels. Here, we shed light on these issues in long-lived female Eiders (Somateria mollissima) by investigating how current reproductive investment (clutch size) and hatching success relate to faecal glucocorticoid metabolite [fGCM] level and residual reproductive value (minimum years of breeding experience, body condition, relative telomere length) under spatially variable predation risk. Our results showed a positive relationship between colony-specific predation risk and mean colony-specific fGCM levels. Clutch size and female fGCM were negatively correlated only under high nest predation and in females in good body condition, previously shown to have a longer life expectancy. We also found that younger females with longer telomeres had smaller clutches. The drop in hatching success with increasing fGCM levels was least pronounced under high nest predation risk, suggesting that elevated fGCM levels may allow females to ensure some reproductive success under such conditions. Hatching success was positively associated with female body condition, with relative telomere length, particularly in younger females, and with female minimum age, particularly under low predation risk, showing the utility of these metrics as indicators of individual quality. In line with a trade-off between current and future reproduction, our results show that high potential for future breeding prospects and increased predation risk shift the balance toward investment in future reproduction, with glucocorticoids playing a role in the resolution of this trade-off.

Signaling, Agonistic Behavior, and Life-History Traits of Steppe Agama (<i>Trapelus sanguinolentus</i>) in Prague Zoo

Life history traits are influenced by many factors, such as social structure, social displays and aggressive interactions. We investigated signalling and agonistic behavior in relation to body condition and lifespan in Trapelus sanguinolentus, a small, semi-arboreal, oviparous agamid lizard from the Central Asia. We individually examined basic morphological characteristics, number of performed signal displays and relative success in agonistic interactions (via Clutton-Brock index). Life expectancy of males did not differ from life expectancy of females. Overall variability of signals was low and simple push-up display was prevalent signal type for both sexes. Frequency of performed signals differed between sexes with males signalling more. For both sexes number of signals was not associated with life expectancy. Interaction of life expectancy and sex was also not significant. In females — body condition influenced number of performed signals when individuals in better body condition signalled more. Most of agonistic interactions was solved by means of signal displays and did not lead to a direct physical combat. While in males association between CBI and number of signals was not significant, in females higher value of CBI means more performed signals. Conditions of our study (sex ratio 4:1 in favor of females, 20 individuals on 16.5 m2 of terrarium) means that agonistic signals have greater importance for females. The agonistic interactions in females led to direct physical combat more frequently could reflect more competitive intra-sexual environment. Females in better body condition probably used higher signalling activity and better performance in direct combat for access to mates and to places for sunbathing and oviposition.

Effects of rearing conditions on natal dispersal processes in a long-lived predator bird.

Natal or prebreeding dispersal is a key driver of the functioning, dynamics, and evolution of populations. Conditions experienced by individuals during development, that is, rearing conditions, may have serious consequences for the multiple components that shape natal dispersal processes. Rearing conditions vary as a result of differences in parental and environmental quality, and it has been shown that favorable rearing conditions are beneficial for individuals throughout their lives. However, the long‐term consequences of rearing conditions on natal dispersal are still not fully understood in long‐lived birds. In this study, we aim to test the following hypotheses to address the relationship between rearing conditions and certain components of the natal dispersal process in Bonelli’s eagle (Aquila fasciata): (1) The body condition of nestlings depends on the quality of the territory and/or breeders; and (2) the survival until recruitment, (3) the age of recruitment, and (4) the natal dispersal distance (NDD) all depend on rearing conditions. As expected, nestlings reared in territories with high past productivity of chicks had better body condition, which indicates that both body condition and past productivity reflect the rearing conditions under which chicks are raised. In addition, chicks raised in territories with high past productivity and with good body condition had greater chances of surviving until recruitment. Furthermore, birds that have better condition recruit earlier, and males recruit at a younger age than females. At last, although females in good body condition exhibited higher NDD when they recruited at younger ages, this pattern was not observed in either older females or males. Overall, this study provides evidence that rearing conditions have important long‐term consequences in long‐lived birds. On the basis of our results, we advocate that conservation managers work actively in the promotion of actions aimed at improving the rearing conditions under which individuals develop in threatened populations.

Reproductive Ecology of Recently Established Wild Pigs in Canada

An essential component of management efforts to control invasive species is the estimate of life history parameters, such as reproductive rate and litter size. Wild pigs (Sus scrofa), one of the most invasive terrestrial mammals worldwide, have recently become established on the Canadian prairies. We estimated life history traits in a population of wild pigs in Saskatchewan, Canada, at the current northern limit of their North American distribution. The average pregnant wild pig weighed 73.8 kg (46 – 130 kg; n = 7). Fifty-four percent of females ≥46 kg were pregnant in Feb., with an average of 5.6 fetuses per pregnant female (range 4 – 7; n = 7). Although small sample sizes precluded statistical significance, we found that larger females in better body condition tended to have more fetuses and that the sex ratio of fetuses tended to be female-biased. Based on the cohort that we sampled in Feb., we predicted parturition would occur between Feb. and May; this range of parturition dates may have been wider had we sampled wild pigs at other times of the year. We show that the number of fetuses of wild pigs in Saskatchewan is similar to other areas, suggesting that population growth and spread could be just as rapid. Our estimates represent the first empirical life history measures of wild pigs in Canada and are an essential step in developing science-based eradication plans for this highly invasive species.

Geographical variation in sexual behavior and body traits in a sex role reversed wolf spider.

Mating partners need to recognize, assess each other, and exchange information through behavioral events that occur before, during, and after mating. Sexual signals, as well as life history traits, are influenced by selective pressures and environmental factors that can vary across distant geographical areas. Allocosa senex is a sand-dwelling wolf spider which constructs burrows along the sandy coasts of Argentina, Brazil, and Uruguay. Females are the mobile sex that searches for males and initiates courtship. They prefer males which construct longer burrows, and males prefer virgin females in good body condition. The objective of this study was to compare sexual behavior patterns, as well as body characteristics and burrow dimensions, between two geographically distant locations of A. senex, one in Uruguay (Uruguayan location) and the other from central Argentina (Argentinean location). We found differences in the number of male abdominal vibrations, male and female touches during mating, and number of erections of male leg spines, which all were higher in matings of Argentinean pairs. On the other hand, male body mass and female body condition were higher in Uruguayan individuals. The wide distribution of A. senex could be determining variations in the biotic and abiotic features that affect the species, generating differences in the strength of selective forces acting on individuals from the two studied locations.

Biliverdin- and protoporphyrin-based eggshell pigmentation in relation to antioxidant supplementation, female characteristics and egg traits in the canary (Serinus canaria)

Avian eggs exhibit a large variability in coloration and patterns, which are produced by blue-green biliverdin and red-brown protoporphyrin pigments. Several hypotheses have been proposed to explain the function of eggshell coloration. In this experimental study, we tested two hypotheses (signalling-function hypothesis and structural-function hypothesis) on both eggshell pigment types in an open-nesting songbird, the canary (Serinus canaria). Also, we aimed to examine whether deposition of pigments into the eggshell has any cost in terms of the plasma oxidative status of the female. We found that eggshell average blue-green chroma was increased by antioxidant supplementation, although we note that there had already been a pre-existing bias in plasma antioxidant capacity between the supplemented and control groups. Eggshell average blue-green chroma was positively related to female body condition during egg laying. However, blue-green eggshell colour was not related to female oxidative status during or after the laying period, and blue-green chroma increased with laying order. Accordingly, we found some support for that eggshell blue-green colour could reflect maternal antioxidant availability and body condition, but did not find evidence that it has a cost for the female’s oxidative status. By contrast, eggshell spot brightness was positively related to body condition, suggesting that darker spotting reflected poorer nutritional condition in the canary. Eggshell blue-green pigmentation was not significantly connected to the egg volume or yolk antioxidant level, but we found that eggs with lower yolk antioxidant concentration had higher average eggshell brown chroma. In sum, our results suggest that eggshell colour reflected female antioxidant and nutrient availability. Finally, we found that eggs with thinner eggshells had a more aggregated spot distribution, supporting the view that aggregated spots may help to strengthen eggshells. Avian eggs have a large variability in colours and patterns, which are due to two pigments: the blue-green biliverdin and the red-brown protoporphyrin. In this study, we tested whether eggshell pigmentation, measured by a spectrophotometer, could reflect female and egg quality in the canary, an open nesting songbird. We found that females supplemented with antioxidants before and during egg-laying laid more intense blue-green eggs. Females in better body condition laid eggs that had a more intense blue-green coloration, but lower intensity of brown coloration. Egg yolk antioxidant level was lower in eggs with more intense brown eggshell coloration. These results suggest that eggshell coloration could reflect the antioxidant and nutrient availability of females. Moreover, we found that eggs with thinner eggshells had a more aggregated spot distribution on the eggshell, supporting the view that aggregated brown pigment spots may help to strengthen eggshells.

Heterogeneity in reproductive success explained by individual differences in bite rate and mass change

Allocation of resources to current reproduction may reduce future reproduction, growth, and survival, but individual heterogeneity in resource acquisition may obscure this fitness cost. In capital breeders, heterogeneity in reproductive success is often related to body mass or condition, underlining the importance of stored reserves for reproduction. Heterogeneity in the rate of resource acquisition could also affect reproduction. Resource acquisition depends on food intake, but the effects of individual foraging rate on mass gain and reproductive success in wild herbivorous mammals are unknown. We measured how individual bite rate affected mass change and reproductive success of 55 female eastern gray kangaroos (Macropus giganteus) over 2 years. Females with faster bite rate had greater subsequent mass gain, leading to greater offspring survival. In one of 2 years, bite rate directly increased juvenile survival to 8 months. Bite rate appeared to have a direct effect on survival to weaning for young born to females with above-average mass gain, particularly for females in better body condition. Independent of bite rate, individual mass change explained most of the variation in offspring survival. We found a weak positive effect of body condition on reproductive success, suggesting that condition affected reproductive success through its effect on mass change and bite rate. Kangaroos appeared to combine income and capital breeding strategies to deal with internal and external constraints on resource allocation. Our study underlines the importance of accounting for different sources of individual heterogeneity that may affect trade-offs among life-history traits, with important consequences for population dynamics and the evolution of reproductive strategies.

Personality, body condition and breeding experience drive sociality in a facultatively social bird

Adopting different behavioural strategies may reduce within-group conflict, selecting for behavioural consistency (‘personality’). Personality may also affect grouping tendencies. The relationship between the personality dimensions sociability and boldness nevertheless remains unclear. This knowledge gap may reflect a failure to consider potential trade-offs between avoiding conspecifics, potentially alleviating social stress, and avoiding predation. Furthermore, the effects of personality and state (e.g. body condition or age affecting the costs and benefits of behavioural actions) on cooperativeness should be considered together. This is because state may explain predation vulnerability, which may affect boldness under predation risk, and thus antipredator grouping tendencies. To address the problem, we determined how group size preference and group-forming time depended on boldness (flight initiation distance, FID, in response to an approaching human), body condition and breeding experience in facultatively social eiders, Somateria mollissima, where females form coalitions or care for the young solitarily. Breeding adults and young are subject to high predation pressure, providing a strong incentive for brood-tending females to cooperate. Because hormonal differences may also explain differences in sociability, we included baseline and handling-induced serum corticosterone concentrations of incubating females as potential predictors of sociability. We also statistically controlled for availability of potential partners. The relationship between boldness (FID) and the number of coalition partners ranged from negative (females in poor body condition) to positive (females in good body condition), arguing against a uniform relationship between boldness and sociability. The number of coalition partners decreased with female breeding experience. The time taken to form a coalition was shortest close to the hatching peak in the population. Shyness (long FID) delayed group formation. Despite a need for safety in numbers by shy females in poor body condition, their entry into groups may be constrained by their personality, suggesting a possible trade-off between predator and conspecific avoidance.

Maternal body condition influences magnitude of anti-predator response in offspring.

Organisms exhibit plasticity in response to their environment, but there is large variation even within populations in the expression and magnitude of response. Maternal influence alters offspring survival through size advantages in growth and development. However, the relationship between maternal influence and variation in plasticity in response to predation risk is unknown. We hypothesized that variation in the magnitude of plastic responses between families is at least partly due to maternal provisioning and examined the relationship between maternal condition, egg provisioning and magnitude of plastic response to perceived predation risk (by dragonfly larvae: Aeshna spp.) in northern leopard frogs (Lithobates pipiens). Females in better body condition tended to lay more (clutch size) larger (egg diameter) eggs. Tadpoles responded to predation risk by increasing relative tail depth (morphology) and decreasing activity (behaviour). We found a positive relationship between morphological effect size and maternal condition, but no relationship between behavioural effect size and maternal condition. These novel findings suggest that limitations imposed by maternal condition can constrain phenotypic variation, ultimately influencing the capacity of populations to respond to environmental change.

Parental investment in eggs and its effect on nestling growth and survival in Magellanic Penguins

Life-history variables evolve in response to cost-benefit trade-offs. For birds, larger eggs are thought to be beneficial for development of offspring but are energetically costly to produce. Further, egg-size dimorphism within or between clutches can vary with proximate and ultimate causes. We undertook a correlational study to evaluate parental investment in eggs by Magellanic Penguins (Spheniscus magellanicus) and how it affects the growth and survival of nestlings in Puerto Deseado, Argentina, over 3 years. We evaluated the variables that affected egg-volume and yolk-area (using a nondestructive technique), and determined the effects of egg-volume and yolk-area on growth and survival of young. Females in good body-condition laid larger second eggs and, in good years (i.e. years of high reproductive success in the colonies of the study area), yolk-area of second eggs was larger than that of first eggs. We found a positive association between egg-volume and nestling body-size and yolk-area was positively related to nestling survival. Our results suggest that the size of eggs within clutches varied with year and female body-condition. Moreover we demonstrate for the first time that yolk-area is a strong predictor of nestling survival in Magellanic Penguins.

Female body condition affects foetal growth in a capital breeding mysticete

Summary Understanding how female body condition (FBC) influences foetal development, and hence offspring production, is fundamental for our understanding of species reproductive physiology and life history. We investigated the effects of FBC on foetus growth in common minke whales. Pregnant minke whales were sampled around Iceland during the summer feeding seasons between 2003 and 2007 and the length and weight of their foetuses were measured. FBC was modelled as the relative difference between measured blubber volume and the average expected blubber volume of individual whales. Generalized linear models were used to test the effect of FBC on foetus length, while accounting for the daily growth in foetus size through gestation, as well as other covariates. Foetus length increased curvilinearly through the study period at an average rate of 0·964 cm day−1 (SE = 0·138). The effect of FBC on foetal length was nonlinear, showing an almost linear positive relationship for females in poorer body condition (FBC < 0), which levelled off at better body conditions (FBC > 0). The curvilinear relationship between FBC and foetus growth was confirmed by fitting a generalized additive model and by running separate analyses on two subsets of data separating females in poorer and better condition. Our findings suggest that females that are in poorer body condition reduce their energetic investment in their foetus proportionately to their condition, most likely to help maintain a high survival probability. That foetus length did not increase for females in better body condition suggests that females have an upper limit on the amount of energy they will or can invest in their foetus. Reducing the size at birth by reducing the gestation period is also unlikely, because the reproductive cycle of balaenopterids is strongly linked to their seasonal migration between feeding grounds and breeding grounds. This study is the first to demonstrate that FBC can affect foetus growth in a capital breeding mysticete.

Integument colouration in relation to persistent organic pollutants and body condition in arctic breeding black-legged kittiwakes (Rissa tridactyla)

Vertebrates cannot synthetize carotenoids de novo but have to acquire them through their diet. In birds, carotenoids are responsible for the yellow to red colouration of many secondary sexual traits. They are also involved in physiological functions such as immunostimulation and immunoregulation. Consequently, carotenoid-based colouration is very often considered as a reliable signal for health and foraging abilities. Although a few studies have suggested that carotenoid-based coloured traits could be sensitive to environmental pollution such as persistent organic pollutants (POPs) contamination, the relationships between pollutants and colouration remain unclear. Here, we examined the relationships between the colouration of carotenoid-based integuments and individual POP levels in pre-laying female black-legged kittiwakes from very high latitudes. In this area, these arctic seabirds are exposed to high POPs contamination. Additionally, we investigated the relationships between colouration and body condition, a frequently used index of individual quality. We found a negative relationship between POP levels and several components of integument colouration: saturation of eye-ring, gapes and tongue, suggesting that POPs could disrupt colouration of labile integuments in female kittiwakes. In addition, we found that females in better body condition displayed more orange and brighter gapes and tongue than females in poor body condition. These results demonstrate that hue and brightness are sensitive to the current health and nutritional status of female kittiwakes. Overall, our study shows that carotenoid-based colour integuments can be affected by several environmental-driven variables.

Context dependency of baseline glucocorticoids as indicators of individual quality in a capital breeder

Identifying markers of individual quality is a central goal of life-history theory and conservation biology. The ‘corticosterone (CORT)-fitness hypothesis’ postulates that low fitness signals impaired ability to cope with the environment, resulting in elevated baseline CORT levels. CORT can, however, be negatively, positively or neutrally related to fitness, depending on the context. In order to clarify this controversial issue, we elucidate the utility of using baseline CORT as a correlate of individual fitness in incubating female eiders across variable environments. An increase in serum CORT with decreasing body condition was evident in older, more experienced breeders, while increased clutch mass was associated with elevated serum CORT in females breeding late in the season. For faecal CORT, the expected negative association with body condition was observed only in early breeders. We found a strong increase in faecal CORT with increasing baseline body temperature, indicating the utility of body temperature as a complementary stress indicator. Females in good body condition had a lower baseline body temperature, but this effect was only observed on open islands, a harsher breeding habitat less buffered against weather variability. Females with higher reproductive investment also maintained a lower baseline body temperature. Nest success strongly decreased with increasing serum and faecal CORT concentrations, and individual stress hormone and body temperature profiles were repeatable over years. Although our data support the tenet that baseline CORT is negatively related to fitness, the complex context-dependent effects call for cautious interpretation of relationships between stress physiology and phenotypic quality.

Stress responsiveness, age and body condition interactively affect flight initiation distance in breeding female eiders

Predation may drive differential selection among personality types, but the mechanism linking personality with predation risk is poorly understood. One such mechanism may be provided by stress hormones (corticosterone in birds), which are linked to boldness towards predators. However, because of feedbacks between boldness and future fitness expectations, the relationship between boldness and stress physiology may be modulated by individual quality. We investigated flight initiation distances (FIDs) of incubating eider, Somateria mollissima, females in relation to handling-induced corticosterone concentrations and individual quality (female breeding experience, body condition). We investigated whether FIDs were repeatable, and whether stress responsiveness and individual quality attributes, either independently or interactively, affected FIDs. We also analysed whether incubation duration, a period of peak predation pressure on females, would depend on female boldness towards predators (FID), controlling for individual quality. FIDs were repeatable within and between seasons, and females with higher handling-induced corticosterone concentrations generally had longer FIDs. However, this relationship was modulated by interactions between stress responsiveness and individual quality. High stress responsiveness was associated with longer FIDs in younger females, while the opposite was found for the oldest females. Furthermore, the FIDs of females in good body condition increased less strongly with increasing stress-induced circulating corticosterone. Shy females (long FIDs) and those in poor body condition had shorter incubation periods. Boldness is thus linked to stress responsiveness, helping to explain why stress responses may be correlated with survival. However, physiological stress effects on boldness cannot be understood in isolation from effects of individual quality.

Male sexual cannibalism in a sand-dwelling wolf spider with sex role reversal

Sexual cannibalism usually involves females attacking and consuming males before, during or after copulation. Sex role reversed systems may provide insight into the debate about whether it arises as mistaken identity, a spillover in female aggressiveness, foraging decisions, and/or extreme mate choice. In such systems, males may be selective and voracious to compensate for their higher reproductive costs, and thus males may be the sexually cannibalistic sex. Allocosa brasiliensis shows a reversal in sex roles and male-biased sexual size dimorphism (the opposite of the common pattern in spiders). The present study aimed to test whether males cannibalize or mate according to female reproductive status or body characteristics. Each of 20 adult males was consecutively exposed to one virgin and one mated female, alternating the order of exposure. Males preferred to mate with virgin females in good body condition and heavier-mated females. Males attacked 15% of virgins and 40% of mated females and cannibalized 10% and 25% of the total trials, respectively. The astonishing male cannibalistic behaviour best agrees with extreme mate choice hypotheses because attacks were more frequent on mated females of low body condition. This is the first report of male sexual cannibalism in a sex role reversed system. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 68–75.