Group histories and offspring sex ratios in ringtailed lemurs (Lemur catta)

Birth sex ratios were examined for ringtailed lemurs (Lemur catta) at the Duke University Primate Center. This population provides a long-term database of births under a variety of demographic and management conditions, including two semi-freeranging groups between which males transfer freely and females defend stable territorial boundaries. We examined three hypotheses usually considered in studies of primate sex ratio bias. The Trivers-Willard hypothesis predicts that dominant females produce males, local resource competition at the population level (LRC-population) predicts that the dispersing sex (males) will be overproduced in dense populations, and local resource competition among individuals (LRC-individual) predicts that dominant females overproduce the philopatric sex (females). We also examined a fourth hypothesis, local resource enhancement (LRE), which is usually subsumed under LRC-individual in studies of primate sex ratio evolution. LRE predicts that under certain conditions, females will produce the sex that provides later cooperative benefits, such as alliance support for within- or between-group competition. Our data provide support for LRE: females overproduce daughters given prospects of new group formation, either through group fission or threatened expulsion of young mothers. Behavioral data from Duke and also wild populations show that daughters serve mothers as important allies in this context and LRE effects also have been documented in other mammals that experience similar group histories. Nonsignificant trends in the data supported the LRC-population hypothesis, and we suggest that LRC interacts with LRE to explain offspring sex ratios in ringtailed lemurs. Received: 27 August 1999 / Received in revised form: 6 March 2000 / Accepted: 18 March 2000     

Reproductive success in a low skew, communal breeding mammal: the banded mongoose, Mungos mungo

In most cooperatively breeding species, reproduction is monopolised by a subset of group members. However, in some species most or all individuals breed. The factors that affect reproductive success in such species are vital to understanding why multiple females breed. A key issue is whether or not the presence of other breeders is costly to an individual’s reproductive success. This study examines the factors that affect the post-parturition component of reproductive success in groups of communal-breeding banded mongoose (Mungos mungo), where up to ten females breed together. Per-litter reproductive success was low (only 18% of pups survived from birth to independence). Whilst singular breeding was wholly unsuccessful, there were costs associated with breeding in the presence of increasing numbers of other females and in large groups. Synchronisation of parturition increased litter success, probably because it minimises the opportunity for infanticide or decreases competitive asymmetry between pups born to different females. There was no evidence of inbreeding depression, and reproductive success was generally higher in litters where females only had access to related males within their group. I conclude that communal breeding in female banded mongooses represents a compromise between the benefits of group-living and communal pup care on the one hand, and competition between females to maximise their personal reproductive success on the other. Such conflicts are likely to occur in most communal breeding species. Whilst communal breeding systems are generally considered egalitarian, negative effects of co-breeders on individual reproductive success is still an issue.     

Cooperatively breeding superb fairy-wrens show no facultative manipulation of offspring sex ratio despite plausible benefits

We report a long-term study of offspring sex ratios in the cooperatively breeding superb fairy-wren Malurus cyaneus. Detailed study of this species had revealed a suite of potentially strong selection pressures on the sex ratio. First, females gain substantial fitness benefits from the presence of helpers; so females without male helpers would benefit from any strategy that increased the probability of recruiting help, such as overproduction of sons (local resource enhancement hypothesis), but large numbers of helper males compete among themselves, favouring the production of daughters (local resource competition). Second, daughters fledged early in the season have far greater chances of recruitment to the breeding population than late-fledged daughters, so mothers would benefit from production of daughters early in the breeding season (early bird hypothesis). Third, extra-group mate choice imposes strong sexual selection on males, suggesting that females mating with attractive sires could benefit from investing in sons (sexual selection hypothesis). However, the predictions from these and other sex ratio hypotheses were rejected. The only convincing evidence for manipulation of the sex ratio was a slight bias towards sons (11 sons to 10 daughters) that occurred regardless of context. This result does not support current theory.     

Exogenous testosterone increases female aggression in the European starling (<Emphasis Type="Italic">Sturnus vulgaris</Emphasis>)

In the European starling, Sturnus vulgaris, optimal mating systems differ between males and females. Males gain from polygyny, whereas monogamy increases female fitness. The cost of polygyny to females lead to intense female–female competition, and it has previously been shown that the intensity of female aggression during the pre-breeding period can predict the realised mating system. The physiological regulation of such female aggression in starlings is not yet known. This study examines the role of testosterone in mediating aggressive behaviours involved in intra-specific reproductive competition in female starlings. Testosterone levels were experimentally elevated with testosterone implants in females during the pre-laying period. To simulate a situation in which an additional female tried to mate with the focal female’s mate, a caged female was presented close to a nest-site to which the male could attract a secondary female. Testosterone was significantly related to several behaviours involved in female–female interactions. Females with testosterone implants spent significantly more time close to the caged female and produced more song bouts than control females. In contrast, male behaviour was unrelated to the experimental status of the mate. Females mated to males that attracted a secondary female were less aggressive towards the caged female than those that remained monogamously mated. The effect of exogenous testosterone in this study indicates that androgens may mediate social behaviours in female starlings during the breeding season.     

Offspring sex ratios reflect lack of repayment by auxiliary males in a cooperatively breeding passerine

The repayment hypothesis posits that primary sex ratios in cooperative species should be biased towards the helping sex because these offspring “repay” a portion of their cost through helping behavior and therefore are less expensive to produce. However, many cooperatively breeding birds and mammals do not show the predicted bias in the primary sex ratio. Recent theoretical work has suggested that the repayment hypothesis should only hold when females gain a large fitness advantage from the presence of auxiliary adults in the group. When auxiliaries provide little or no fitness advantage, competition between relatives should lead to sex ratios biased towards the dispersing (non-helping) sex. We examined the benefits auxiliaries provide to females and corresponding offspring sex ratios in the red-backed fairy-wren (Malurus melanocephalus), a cooperatively breeding Australian bird with male auxiliary helpers. We found that auxiliaries provide little or no benefit to female reproductive success or survival. As predicted, the population primary sex ratio was biased towards daughters, the dispersing sex, and females with auxiliaries produced female-biased broods whereas females without auxiliaries produced unbiased broods. Moreover, offspring sex ratios were more strongly biased toward females in years when auxiliaries were more common in the population. These results suggest that offspring sex ratios are associated with competition among the non-dispersing sex in this species, and also that females may use cues to assess local breeding opportunities for their offspring.     

White tail plumage and brood sex ratio in dark-eyed juncos (<Emphasis Type="BoldItalic">Junco hyemalis thurberi</Emphasis>)

Theory, empirical examples, and recently, proximate mechanisms point to the possibility of adaptive sex ratio adjustment in various organisms. General predictions state that a female should adjust her offspring sex ratio to maximize the benefits or minimize the costs of reproduction given her physical condition or current social and environmental conditions. I tested for an influence of male attractiveness on brood sex ratio in a population of dark-eyed juncos (Junco hyemalis thurberi) by manipulating a male’s white outer tail feathers (“tail white”). Experimentally increasing male tail white did not significantly affect sex ratio, nor was premanipulated male tail white significantly related to brood sex ratio. However, the amount of white on the female’s outer tail feathers, independently of female condition, was positively related to the number of sons in a brood. Determining how a female’s potential genetic contribution to her sons’ attractiveness influences offspring sex ratio should be a priority for future research.     

Sociality,Bateman’s gradients,and the polygynandrous genetic mating system of round-tailed ground squirrels (<Emphasis Type="Italic">Xerospermophilus tereticaudus</Emphasis>)

Historically, most mammals have been classified as polygynous; although recent molecular evidence suggests that many mammals may be polygynandrous, particularly the ground-dwelling sciurids. We genotyped 351 round-tailed ground squirrels (Xerospermophilus tereticaudus) using seven microsatellite loci to determine paternity in 31 litters from 2004 to 2007. Polygyny was evident in all years except in 2007, when the population size was reduced. Multiple paternity occurred in the majority of litters (55%) with 2.5 ± 0.26 sires/litter (n = 31). Forty-nine percent of resident males (n = 114) sired offspring, and of males that sired offspring (n = 56) 27% sired young in multiple litters in a single breeding season. Litter size was positively correlated with the number of sires. Through an indirect analysis of paternity, we found 21 litters (68%) with an average relatedness of 0.5 or less. Males had a greater opportunity for sexual selection (I _s = 1.60) than females (I _s = 0.40); Bateman’s gradient was also greater in males (1.07 ± 0.04, n = 56) than females (0.82 ± 0.08, n = 31). The mating system in round-tailed ground squirrels defined through genetic analyses and Bateman’s gradients is polygynandrous compared to the previously suggested polygynous mating system as established by behavioral observations and fits within the predictions of the ground squirrel sociality models. Upon evaluating the predictions of the sociality models among sciurid species, we found a negative relationship between the level of sociality with litter size and the average percentage of multiple paternity within a litter. Thus, recent genetic information and reclassification of mating systems support the predictions of the ground-dwelling squirrel sociality models.     

Behavioral and demographic changes following the loss of the breeding female in cooperatively breeding marmosets

Recent models of the evolution and dynamics of family structure in cooperatively breeding vertebrates predict that the opening of breeding vacancies in cooperatively breeding groups will result in (1) dispersal movements to fill the reproductive position, and (2) within-group conflict over access to reproduction. We describe the behavioral and demographic changes that followed the creation of breeding vacancies in three wild groups of cooperatively breeding common marmosets (Callithrix jacchus). Replacement of the breeding female was rapid when no adult females remained in the group, but did not occur for several months when other adult females were present. Aggression of adult animals towards same-sex potential immigrants was associated with a period of reduced affiliation, increased intragroup agonism, no intragroup sexual behavior, and frequent extragroup copulations. This ended with the fissioning of groups along sexual lines. After replacement, multiple males copulated with multiple females and vice versa, with no increases in sexually related aggression. Female-female conflict was resolved through infanticide. The lack of direct conflict between males is consistent with cooperative polyandry. After a breeding vacancy appeared, marmoset groups showed conflict of interests among group members similar to those shown by cooperatively breeding birds, but they used different behavioral mechanisms to resolve those conflicts. Our data provide important evidence from a cooperatively breeding mammal to support Emlen’s model for the evolution of vertebrate families, but they suggest that species-specific inter- and intrasexual competitive strategies should be considered before the model can be applied to other cooperatively breeding vertebrates. Received: 23 November 1999 / Received in revised form: 28 March 2000 / Accepted: 1 April 2000     

Sex allocation in Savi’s warblers <Emphasis Type="Italic">Locustella luscinioides</Emphasis>: multiple factors affect seasonal trends in brood sex ratios

Sex allocation theory predicts that whenever the relative fitness of sons and daughters differ, females should invest more in the sex with the greatest fitness return. In this study, we evaluated the influence of various ecological factors on the brood sex ratio (BSR) of Savi’s warblers (Locustella luscinioides) across several breeding seasons. There was a slight but significant female production bias at the population level, which is consistent with the ‘local resource competition’ hypothesis, as the breeding density is very high and females are more prone to disperse. We found that there was a significant decline in BSR during the breeding season, but no influence of male size, female size, social status nor extra-pair paternity were detected. The seasonal decline in BSR was further evaluated by assessing the within- and between-female effects, which indicated that multiple factors were operating simultaneously in our study population. First, there was a significant within-female decline in BSR, which was consistent with the decline in female condition due to the reproductive effort associated with multiple brooding (supporting the Trivers and Willard hypothesis). Second, a significant decline in BSR with the laying date of first clutches of different pairs indicated that male and/or female qualities are also associated with the seasonal variation in BSR. Finally, a comparison between the sex of the youngest nestling with the remaining ones did not suggest any bias, indicating that females do not compensate for the increased mortality of the last nestling (caused by asynchronous hatching) by producing a male from the last laid egg.     

Temperature,age of mating and starvation determine the role of maternal effects on sex allocation in the mealybug <Emphasis Type="Italic">Planococcus citri</Emphasis>

Environmental effects on sex allocation are common, yet the evolutionary significance of these effects remains poorly understood. Environmental effects might influence parents, such that their condition directly influences sex allocation by altering the relative benefits of producing sons versus daughters. Alternatively, the environment might influence the offspring themselves, such that the conditions they find themselves in influence their contribution to parental fitness. In both cases, parents might be selected to bias their sex ratio according to the prevailing environmental conditions. Here, we consider sex allocation in the citrus mealybug Planococcus citri, a species with an unusual genetic system in which paternal genes are lost from the germline in males. We test environmental factors that may influence either female condition directly (rearing temperature and food restriction) or that may be used as cues of the future environment (age at mating). Using cytological techniques to obtain primary sex ratios, we show that high temperature, older age at mating and starvation all affect sex allocation, resulting in female-biased sex ratios. However, the effect of temperature is rather weak, and food restriction appears to be strongly associated with reduced longevity and a truncation of the usual schedule of male and offspring production across a female’s reproductive lifetime. Instead, facultative sex allocation seems most convincingly affected by age at mating, supporting previous work that suggests that social interactions experienced by adult P. citri females are used when allocating sex. Our results highlight that, even within one species, different aspects of the environment may have conflicting effects on sex allocation.     

Parental investment, adult sex ratios, and sexual selection in a socially monogamous seabird

Although most birds are monogamous, theory predicts that greater female parental investment and female-biased adult sex ratios will lower the polygyny threshold. This should result in polygynous mating, unless obligate biparental care or the spatial and temporal distribution of fertilizable females constrains a male’s ability to take advantage of a lowered polygyny threshold. Here we present data on the extent of male sexually dimorphic plumage, adult sex ratios and breeding season synchrony in three populations of a socially monogamous seabird, the brown booby Sula leucogaster. For one of these populations, San Pedro Mártir Island, we also present data on differences in male and female parental investment, mortality and probability of pairing. The extent of plumage dimorphism varied among populations. Sex ratios were female biased in all populations. On San Pedro Mártir Island, parental investment was female biased, females failed more often than males to find a mate, but there was no polygyny. We suggest that on San Pedro Mártir: (1) a period of obligate biparental care coupled with a relatively synchronous breeding season constrained the ability of males to take advantage of a high environmental polygamy potential and (2) the resulting socially monogamous mating system, in combination with the female-biased adult sex ratio, caused females to be limited by the availability of males despite their greater parental investment. Received: 18 November 1999 / Accepted: 24 January 2000     

Multiple insemination increases reproductive success of female Montandon’s newt (<Emphasis Type="Italic">Triturus montandoni</Emphasis>, Caudata,Salamandridae)

The adaptive significance of multiple matings for females is a matter of much controversy. In insects, supplying the female’s sperm reserves with portions of fresh spermatozoa may be the main function of multiple matings. This simple explanation may also be applied to other animals which produce large numbers of eggs over prolonged periods of time. We tested the fertility insurance hypothesis in Montandon’s newt (Triturus montandoni, Amphibia, Salamandridae). T. montandoni females are inseminated internally by spermatophores they have picked up, and subsequently lay eggs fertilized by spermatozoa released from the spermatheca. We compared the reproductive success of singly and multiply inseminated females of Montandon’s newt in the laboratory. Multiply inseminated females laid more eggs and had a lower percentage of non-developing eggs than females who mated only once. Our data suggest that remating increases the reproductive success of multiply inseminated females by replenishing sperm reserves in the spermatheca or by supplying females with fresh portions of spermatozoa with high fertilizing capacity. Received: 7 January 2000 / Revised: 13 September 2000 / Accepted: 7 October 2000     

Offspring sex ratio in relation to female size in southern elephant seals,Mirounga leonina

Southern elephant seals Mirounga leonina display extreme sexual dimorphism. In addition females show great variation in size and stored resources at parturition. Therefore they present an excellent opportunity for examination of responses of sex ratio to resource availability. We studied the relationships between the size of southern elephant seal females at parturition and the size and sex of their pups at South Georgia over four breeding seasons. We found a large individual variation in maternal post-partum mass (range 296–977 kg, n=151). Larger mothers gave birth to larger pups, irrespective of the sex of their pup. Male pups were on average 14% larger than females at birth and consequently more costly to bring to parturition. Our results suggest that female southern elephant seals must weigh more than 300 kg if they are to breed at all, and more than 380 kg if they are to give birth to a male pup. Above this threshold the proportion of males among offspring rapidly increases with maternal mass, and stabilizes at a level not significantly different from parity. These results show that smaller females of southern elephant seals vary offspring sex ratio in a way that is consistent with theories on adaptive offspring sex ratio. A smaller mother with a male foetus may benefit from terminating her pregnancy and allocating the resources she saves to her own growth. She could then give birth to and raise a larger pup in the subsequent season.     

Geographical patterns in reproductive biology of the Pan-American sandy beach isopod<Emphasis Type="Italic"> Excirolana braziliensis</Emphasis>

Eleven populations of the Pan-American sandy beach isopod Excirolana braziliensis, distributed from tropical (9°N) to temperate (39°S) sandy beaches in Atlantic and Pacific Oceans, were analyzed to determine latitudinal variations in: breeding and recruitment patterns, sex ratios, size of ovigerous females and of juveniles and length–fecundity relationships. E. braziliensis exhibited strong latitudinal patterns in all reproductive traits throughout its distribution range. Breeding and recruitment shifted from continuous to seasonal from tropical to temperate beaches, having a predominance of females at higher latitudes. In agreement with the latitudinal gradient hypothesis, ovigerous females inhabiting tropical sandy beaches (low latitudes) were smaller, became sexually mature at smaller sizes and had lower individual fecundity than on temperate beaches. Juveniles were also smallest at low latitudes. Between-ocean comparisons showed very similar reproductive characteristics for roughly the same latitude. These linked reproductive parameters suggest that the intensity of breeding effort is associated with the duration of the breeding season and geographically size-related characteristics of the species. Geographic variations in the breeding and recruitment seasons, as well as in individual fecundity, size structure of mature females and sex ratios, are proposed to have major consequences in explaining local variations in population demography. Our paper also reinforces the notion that sandy beach animals are highly plastic.Communicated by O. Kinne, Oldendorf/Luhe     

Evidence for seasonal mate limitation in populations of an intertidal amphipod, Corophium volutator (Pallas)

Potential rates of reproduction (PRR) differ between the sexes of many animal species. Adult sex ratios together with PRR are expected to determine the operational sex ratio (OSR) defined as the ratio of fertilizable females to sexually active males at any given time. OSR is expected to determine the degree to which one sex competes for another—the limiting sex. We explored the potential for mate limitation in an intertidal amphipod, Corophium volutator (Pallas). Males have higher PRR than females, but males may be limiting because of extreme female-biased sex ratios observed in this species. Consistent with this idea, late season females were less likely to be ovigerous and had smaller size-specific clutches, both of which were associated with seasonal declines in availability of males of reproductive size. Seasonal changes in ovigery could not be explained by seasonal changes across sites in other factors (e.g., female body size or phenology of breeding). Smaller females were less likely to become ovigerous later in the season at three of four sites. Seasonal reductions in clutch size also occurred among small females expected to be reproducing for their first time. In complimentary laboratory experiments, reduced likelihood of ovigery and reduced fecundity occurred when the number of receptive females was increased relative to availability of a reproductively active male. Our results suggest male mate limitation can occur seasonally in this species and that male limitation is regionally widespread and may affect recruitment.     

Sex ratio manipulation and decreased growth of male offspring of undernourished golden hamsters (Mesocricetus auratus)

Summary The theory that female mammals in poor condition may increase individual fitness by skewing the sex ratio of their offspring toward daughters and by investing more resources in daughters than in sons was tested in hamsters. Newly mated experimental females were food-restricted during pregnancy and lactation (RR) or during lactation only (AR). Controls received food ad libitum. Maternal body weights were assessed daily from mating to 25 days postpartum. Litter survival (% litters with at least one pup surviving on any day), litter size, offspring sex ratios (=% males), and pup weights were monitored daily from birth (Day 1) to Day 25. All control and AR dams gave birth 16 days after mating. Gestation was extended by 1–3 days for 35.4% of RR dams. RR dams weighed significantly less at parturition than controls and AR females. During lactation, AR females showed the greatest weight loss and control females the least. AR weight loss exceeded that of RR females, possibly because the former maintained larger litters. Survival was highest for controls, intermediate for AR, and lowest for RR litters. Mean sex ratio at birth was significantly less for RR (40.7%) than for control (49.6%) and AR (48.8%) litters. RR sex ratio did not change significantly postnatally. Sex ratios of control and AR litters never differed statistically from 50%. Control male pups were significantly heavier than their sisters throughout the experiment. No significant gender differences were observed for AR pup weights after Day 2 postpartum. RR female offspring weighed more than their brothers throughout the experiment, and this difference was statistically significant immediately prior to the time that pups began to feed independently (Days 14–17). RR female pup weights were similar to, and sometimes significantly greater than, weights of control daughters during the period of postnatal maternal investment. Control males were always heavier than males from the other treatments. Patterns of weight gain by AR and RR males varied with age. We conclude that underfed female hamsters are able to adjust the sex ratio of offspring prenatally and parental investment postnatally to favor daughters.     

Dominance status influences female reproductive strategy in a territorial African rodent <Emphasis Type="Italic">Rhabdomys pumilio</Emphasis>

Dominance status influences the fitness of many mammals. Using African striped mice Rhabdomys pumilio, we tested whether (1) dominant females have greater reproductive success than subordinate females, (2) dominant females influence the reproductive output of subordinate females when they are housed in close proximity, (3) reproductive output of a female changes in response to the dominance status of her neighbours, and (4) whether prolonged association between individuals influences the variance in reproductive success between dominants and subordinates (i.e. the ‘dear enemy’ phenomenon). The size and mass of litters of dominants increased significantly when housed adjacent to subordinates than when housed apart. The litter size and mass of subordinates remained unchanged, although subordinates spent significantly more time with their pups when housed close to dominants than when housed apart; time spent with pups by dominants remained unchanged. Moreover, females modified their reproductive output and behaviour in relation to the dominance status of their neighbours. Following prolonged association, dominants still had greater reproductive success, but now, the time spent with pups decreased in subordinates. We suggest that dominants adopt a strategy to increase the reproductive value of their litter, whereas subordinates adopt a pup defence strategy. These strategies are flexible and are influenced by the dominance status and period of association between neighbours, so that females could maximize their fitness in response to varying social conditions.     

Asymmetric larval competition in the parasitoid wasp <Emphasis Type="Italic">Nasonia vitripennis</Emphasis>: a role in sex allocation?

Sex allocation theory offers excellent opportunities for testing how animals adjust their behaviour in response to environmental conditions. A major focus has been on instances of local mate competition (LMC), where female-biased broods are produced to maximise mating opportunities for sons. However, the predictions of LMC theory can be altered if there is both local competition for resources during development and an asymmetry between the competitive abilities of the sexes, as has been seen in animals ranging from wasps to birds. In this paper, we test the extent to which asymmetric larval competition alters the predictions of LMC theory in the parasitoid wasp Nasonia vitripennis. We found that the body size of both sexes was negatively correlated with the number of offspring developing within the host. Further, we found that when faced with high levels of competition, the body size of females, but not males, was influenced by the sex ratio of the competing offspring; females were smaller when a higher proportion of the brood was female. This asymmetric competition should favour less biased sex ratios than are predicted by standard LMC theory. We then develop a theoretical model that can be parameterised with our data, allowing us to determine the quantitative consequences of the observed level of asymmetric larval competition for sex allocation. We found that although asymmetric competition selects for less biased sex ratios, this effect is negligible compared to LMC. Furthermore, a similar conclusion is reached when we re-analyse existing data from another parasitoid species where asymmetric larval competition has been observed; Bracon hebetor. Consequently, we suspect that asymmetric larval competition will have its greatest influence on sex ratio evolution in species that have smaller clutches and where local mate competition is not an issue, such as birds and mammals.     

Breeding Periodicity for Male Sea Turtles,Operational Sex Ratios,and Implications in the Face of Climate Change

Abstract: Species that have temperature‐dependent sex determination (TSD) often produce highly skewed offspring sex ratios contrary to long‐standing theoretical predictions. This ecological enigma has provoked concern that climate change may induce the production of single‐sex generations and hence lead to population extirpation. All species of sea turtles exhibit TSD, many are already endangered, and most already produce sex ratios skewed to the sex produced at warmer temperatures (females). We tracked male loggerhead turtles (Caretta caretta) from Zakynthos, Greece, throughout the entire interval between successive breeding seasons and identified individuals on their breeding grounds, using photoidentification, to determine breeding periodicity and operational sex ratios. Males returned to breed at least twice as frequently as females. We estimated that the hatchling sex ratio of 70:30 female to male for this rookery will translate into an overall operational sex ratio (OSR) (i.e., ratio of total number of males vs females breeding each year) of close to 50:50 female to male. We followed three male turtles for between 10 and 12 months during which time they all traveled back to the breeding grounds. Flipper tagging revealed the proportion of females returning to nest after intervals of 1, 2, 3, and 4 years were 0.21, 0.38, 0.29, and 0.12, respectively (mean interval 2.3 years). A further nine male turtles were tracked for short periods to determine their departure date from the breeding grounds. These departure dates were combined with a photoidentification data set of 165 individuals identified on in‐water transect surveys at the start of the breeding season to develop a statistical model of the population dynamics. This model produced a maximum likelihood estimate that males visit the breeding site 2.6 times more often than females (95%CI 2.1, 3.1), which was consistent with the data from satellite tracking and flipper tagging. Increased frequency of male breeding will help ameliorate female‐biased hatchling sex ratios. Combined with the ability of males to fertilize the eggs of many females and for females to store sperm to fertilize many clutches, our results imply that effects of climate change on the viability of sea turtle populations are likely to be less acute than previously suspected.     

Egg composition in relation to social environment and maternal physiological condition in the collared flycatcher

Offspring survival can be influenced by resources allocated to eggs, which in turn may be affected by the environmental factors the mother experiences during egg formation. In this study, we investigated whether experimentally elevated social interactions and number of neighbouring pairs influence yolk composition of collared flycatchers (Ficedula albicollis). Social challenge was simulated by presentation of a conspecific female. Experimental females spent more time near the cage and produced eggs with higher androgen concentration, but local breeding density did not affect yolk androgen level. Moreover, we found that females exposed to more intra-specific interactions and those that bred at higher density produced eggs with smaller yolk. These females may be more constrained in foraging time due to more frequent social encounters, and there might be increased competition for food at areas of higher density. In contrast, the present study did not reveal any evidence for the effect of social environment on yolk antioxidant and immunoglobulin levels. However, we found that yolk lutein and immunoglobulin concentrations were related to the female’s H/L ratio. Also, yolk lutein and α-tocopherol levels showed a seasonal increase and were positively related to the female’s plasma carotenoid level. Mothers may incur significant costs by transferring these compounds into the eggs, thus only females in good physiological condition and those that lay eggs later, when food is probably more abundant, could allocate higher amounts to the eggs without compromising their defence mechanisms. Our results suggest that environmental circumstances during egg formation can influence conditions for embryonic development.