Reproductive and post‐reproductive life history of wild‐caught Drosophila melanogaster under laboratory conditions

The life history of the fruit fly (Drosophila melanogaster) is well understood, but fitness components are rarely measured by following single individuals over their lifetime, thereby limiting insights into lifetime reproductive success, reproductive senescence and post‐reproductive lifespan. Moreover, most studies have examined long‐established laboratory strains rather than freshly caught individuals and may thus be confounded by adaptation to laboratory culture, inbreeding or mutation accumulation. Here, we have followed the life histories of individual females from three recently caught, non‐laboratory‐adapted wild populations of D. melanogaster. Populations varied in a number of life‐history traits, including ovariole number, fecundity, hatchability and lifespan. To describe individual patterns of age‐specific fecundity, we developed a new model that allowed us to distinguish four phases during a female's life: a phase of reproductive maturation, followed by a period of linear and then exponential decline in fecundity and, finally, a post‐ovipository period. Individual females exhibited clear‐cut fecundity peaks, which contrasts with previous analyses, and post‐peak levels of fecundity declined independently of how long females lived. Notably, females had a pronounced post‐reproductive lifespan, which on average made up 40% of total lifespan. Post‐reproductive lifespan did not differ among populations and was not correlated with reproductive fitness components, supporting the hypothesis that this period is a highly variable, random ‘add‐on’ at the end of reproductive life rather than a correlate of selection on reproductive fitness. Most life‐history traits were positively correlated, a pattern that might be due to genotype by environment interactions when wild flies are brought into a novel laboratory environment but that is unlikely explained by inbreeding or positive mutational covariance caused by mutation accumulation.     

Life history of breeding partners alters age‐related changes of reproductive traits in a natural population of blue tits

Reproductive senescence, an intra‐individual decline in reproductive function with age, is widespread, but proximate factors determining its rate remain largely unknown. Most studies of reproductive senescence focus on females, leaving senescence in male function and its implications for female function largely understudied. We constructed linear mixed models to explore the interactive effects of paternal and maternal age and a life‐history trait (i.e. age at first reproduction) on four fitness components (i.e. laying date, clutch size, number of fledglings and number of recruits) measured in a wild, breeding population of blue tits Cyanistes caeruleus ogliastrae where individual breeding success has been followed for over 30 years (our dataset spanned 29 years). Previous studies have shown that, across female lifespan, laying date decreases and subsequently increases; earlier laying dates result in higher fitness because hatchlings have greater access to a seasonal food source. Our analyses reveal that females that initiate reproduction early in life show a greater delay in laying date with old age. In addition to delayed laying dates, older females lay smaller clutches. However, the magnitude of female age effects was influenced by the age at first reproduction of their breeding partners. Senescence of laying date and clutch size was reduced when females mated with males that reproduced early in life compared to males that delayed reproduction. We confirmed that both laying date and clutch size were significantly correlated with reproductive fitness suggesting that these dynamics early in the breeding cycle can have long‐term consequences. These complex phenotypic interactions shed light on the proximate mechanisms underlying reproductive senescence in nature and highlight the potential importance of cross‐sex age by life‐history interactions.     

Behaviour and reproductive fitness of postdispersal in plateau pikas (<Emphasis Type="Italic">Ochotona curzoniae</Emphasis>) on the Tibetan Plateau

Dispersal, which is a crucial process in animal population and evolutionary ecology, is considered personality dependent. The fitness consequences of dispersal are important. However, they are difficult and rarely measured in wild populations. In this study, we investigated the behaviour and reproductive fitness in a plateau pika (Ochotona curzoniae) population for two continuous years through mark–recapture experiment, behavioural tests and microsatellite analysis of parentage. Our results determined that around 53.8% males and 16.7% females dispersed to 40.3 and 28.2 m away from their natal family, respectively. The aggression (attack frequency and duration) of philopatric individuals was significantly higher than that of dispersed ones, although significant differences in boldness did not exist between them. For both males and females, the offspring number of philopatric pikas was significantly higher than that of dispersed ones. This result indicated that inbreeding may occur in plateau pikas. Our findings highlighted the importance of integrating behavioural, ecological and genetic analyses to explore the mechanism of dispersal. The findings also suggested that personality may play an important role in life history.     

Population genetic evidence for sex‐specific dispersal in an inbred social spider

Dispersal in most group‐living species ensures gene flow among groups, but in cooperative social spiders, juvenile dispersal is suppressed and colonies are highly inbred. It has been suggested that such inbred sociality is advantageous in the short term, but likely to lead to extinction or reduced speciation rates in the long run. In this situation, very low levels of dispersal and gene flow among colonies may have unusually important impacts on fitness and persistence of social spiders. We investigated sex‐specific differences in dispersal and gene flow among colonies, as reflected in the genetic structure within colonies and populations of the African social spider Stegodyphus dumicola Pocock, 1898 (Eresidae). We used DNA fingerprinting and mtDNA sequence data along with spatial mapping of colonies to compare male and female patterns of relatedness within and among colonies at three study sites. Samples were collected during and shortly after the mating season to detect sex‐specific dispersal. Distribution of mtDNA haplotypes was consistent with proliferation of social nests by budding and medium‐ to long‐distance dispersal by ballooning females. Analysis of molecular variance and spatial autocorrelation analyses of AFLPs showed high levels of genetic similarity within colonies, and STRUCTURE analyses revealed that the number of source populations contributing to colonies ranged from one to three. We also showed significant evidence of male dispersal among colonies at one site. These results support the hypothesis that in social spiders, genetic cohesion among populations is maintained by long‐distance dispersal of female colony founders. Genetic diversity within colonies is maintained by colony initiation by multiple dispersing females, and adult male dispersal over short distances. Male dispersal may be particularly important in maintaining gene flow among colonies in local populations.     

Mechanisms and reproductive consequences of breeding dispersal in a specialist predator under temporally varying food conditions

Individual variation in breeding dispersal has extensive ecological and evolutionary consequences, but the factors driving individual dispersal behaviour and their fitness consequences remain poorly understood. Our data on dispersal events of a rodent‐specialist predator, the Eurasian kestrel Falco tinnunculus, over 20 years in western Finland offers a unique opportunity to explore the mechanisms underlying breeding dispersal behaviour and its reproductive consequences in a wild bird population. Sex, age, body condition and previous breeding success affected breeding dispersal. Dispersal distances were longer in females than in males as well as longer in yearlings than in older individuals. Body condition was positively correlated to breeding dispersal distances, particularly for females. The lowest dispersal distances were recorded for intermediate brood sizes in the year preceding dispersal. Our results highlight sex‐ and environment‐specific consequences of breeding dispersal on reproductive performance. During increase phases of the three‐year vole cycles, males dispersing further had lower reproductive performance after dispersal, whereas in females, long breeding dispersal distances were associated with increased breeding success under all environmental conditions. These results suggest benefits associated to breeding dispersal in females, potentially related to large spatio‐temporal variation in main food abundance and intensity of intra‐specific competition. Breeding dispersal of males was costly during increasing food abundance, indicating the potential fitness benefits of environmental familiarity in this migratory species. Overall, our results indicate that both individual traits and environmental factors interact to shape breeding dispersal strategies in wide‐ranging predator populations under fluctuating food conditions.     

Hatching asynchrony can have long‐term consequences for offspring fitness in zebra finches under captive conditions

Hatching asynchrony can have profound short‐term consequences for offspring, although the long‐term consequences are less well understood. The purpose of this study was to examine the long‐term consequences of hatching asynchrony for offspring fitness in birds. Specifically, we aimed to test the hypothesis that hatching asynchrony increases the sexual attractiveness and fecundity, respectively, of early‐hatched male and female zebra finch, Taeniopygia guttata (Vieillot, 1817) offspring. Mate‐choice trials comparing male nestlings with the same parents, but that were reared in asynchronous or experimentally synchronous broods, revealed no female preference in relation to hatching regime. We did however find strong evidence that, as adults, late‐hatched males were more attractive to females than siblings that had hatched earlier. Meanwhile, we found a weak trend towards early‐hatched females depositing more carotenoids and retinol in the egg yolk than late‐hatched or synchronously hatched females, although there were no differences in terms of clutch characteristics or the deposition of α‐tocopherol or γ‐tocopherol in the egg yolk. Therefore, we found that the beneficial long‐term consequences of hatching asynchrony were sex specific, being accrued by late‐hatched male nestlings and by early‐hatched female nestlings. Consequently, we conclude that the long‐term consequences of hatching asynchrony are more complex than previously realised. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 430–438.     

Selection against immigrants in wild seabird populations

Immigration is a major demographic parameter shaping population dynamics and is an important driver of eco‐evolutionary patterns, but the fitness consequences for individuals following their settlement to a new population (immigrants) remain poorly tested in wild animal populations, particularly among long‐lived species. Here we show that immigrants have a lower fitness than residents in three wild seabird populations (wandering albatross Diomedea exulans, southern fulmar Fulmarus glacialoides, snow petrel Pagodroma nivea). Across all species and during a 32‐year period, immigrants made on average ?9 to 29% fewer breeding attempts, had 5–31% fewer fledglings, had 2–16% lower breeding success and produced 6–46% fewer recruits. Female immigration and male residency were also favored through differences in breeding performance. We provide evidence for selection against immigrants in wild populations of long‐lived species and our results are consistent with female‐biased dispersal in birds being driven by asymmetric limiting resources and the competitive ability of dispersers vs. non‐dispersers.     

Fine‐scale genetic structure and helping decisions in a cooperatively breeding bird

In animal societies, characteristic demographic and dispersal patterns may lead to genetic structuring of populations, generating the potential for kin selection to operate. However, even in genetically structured populations, social interactions may still require kin discrimination for cooperative behaviour to be directed towards relatives. Here, we use molecular genetics and long‐term field data to investigate genetic structure in an adult population of long‐tailed tits Aegithalos caudatus, a cooperative breeder in which helping occurs within extended kin networks, and relate this to patterns of helping with respect to kinship. Spatial autocorrelation analyses reveal fine‐scale genetic structure within our population, such that related adults of either sex are spatially clustered following natal dispersal, with relatedness among nearby males higher than that among nearby females, as predicted by observations of male‐biased philopatry. This kin structure creates opportunities for failed breeders to gain indirect fitness benefits via redirected helping, but crucially, most close neighbours of failed breeders are unrelated and help is directed towards relatives more often than expected by indiscriminate helping. These findings are consistent with the effective kin discrimination mechanism known to exist in long‐tailed tits and support models identifying kin selection as the driver of cooperation.     

Declining home range area predicts reduced late‐life survival in two wild ungulate populations

Demographic senescence is increasingly recognised as an important force shaping the dynamics of wild vertebrate populations. However, our understanding of the processes that underpin these declines in survival and fertility in old age remains limited. Evidence for age‐related changes in foraging behaviour and habitat use is emerging from wild vertebrate studies, but the extent to which these are driven by within‐individual changes, and the consequences for fitness, remain unclear. Using longitudinal census observations collected over four decades from two long‐term individual‐based studies of unmanaged ungulates, we demonstrate consistent within‐individual declines in home range area with age in adult females. In both systems, we found that within‐individual decreases in home range area were associated with increased risk of mortality the following year. Our results provide the first evidence from the wild that age‐related changes in space use are predictive of adult mortality.     

Whole‐genome resequencing uncovers molecular signatures of natural and sexual selection in wild bighorn sheep

The identification of genes influencing fitness is central to our understanding of the genetic basis of adaptation and how it shapes phenotypic variation in wild populations. Here, we used whole‐genome resequencing of wild Rocky Mountain bighorn sheep (Ovis canadensis) to >50‐fold coverage to identify 2.8 million single nucleotide polymorphisms (SNPs) and genomic regions bearing signatures of directional selection (i.e. selective sweeps). A comparison of SNP diversity between the X chromosome and the autosomes indicated that bighorn males had a dramatically reduced long‐term effective population size compared to females. This probably reflects a long history of intense sexual selection mediated by male–male competition for mates. Selective sweep scans based on heterozygosity and nucleotide diversity revealed evidence for a selective sweep shared across multiple populations at RXFP2, a gene that strongly affects horn size in domestic ungulates. The massive horns carried by bighorn rams appear to have evolved in part via strong positive selection at RXFP2. We identified evidence for selection within individual populations at genes affecting early body growth and cellular response to hypoxia; however, these must be interpreted more cautiously as genetic drift is strong within local populations and may have caused false positives. These results represent a rare example of strong genomic signatures of selection identified at genes with known function in wild populations of a nonmodel species. Our results also showcase the value of reference genome assemblies from agricultural or model species for studies of the genomic basis of adaptation in closely related wild taxa.     

Maintenance of body‐size variation and host range in the orange‐tip butterfly: evidence for a trade‐off between adult life‐history traits

1. The evolution of host range and preference in phytophagous insects is driven by a female's oviposition choice impacting her offspring's fitness. Analysis of the fitness of progeny on different host plants has commonly been restricted to the performance of immature stages. However, since host use can affect adult size, it is important to measure the ongoing effects of host choice on the resulting imagines. 2. The orange‐tip butterfly, Anthocharis cardamines, shows a strong preference for two host plants in Britain, Alliaria petiolata and Cardamine pratensis, which affect body size. Whilst females exhibit a strong positive size–fecundity relation, the impact of body‐size alteration is unknown in males. In this study, fitness effects of host plant choice for male A. cardamines were examined. 3. Males reared on C. pratensis were smaller and emerged earlier than those reared on A. petiolata, and early‐season males were smaller than late‐season ones in the field. Interestingly, regression analysis indicated that the earlier emergence of small males was a host‐mediated rather than a size‐mediated effect. Small size was associated with reduced male dispersal in a semi‐isolated wild population over a 3‐year period. 4. It is proposed that the earlier emergence associated with C. pratensis has evolved in response to depressed dispersal in isolated/semi‐isolated populations associated with this patchily distributed host. We suggest that adult life‐history traits are important for the maintenance of host range in this species, and offer a critique of Courtney's earlier hypothesis that host range is maintained by time‐limited oviposition behaviour.     

Short‐ and long‐term consequences of early developmental conditions: a case study on wild and domesticated zebra finches

Divergent selection pressures among populations can result not only in significant differentiation in morphology, physiology and behaviour, but also in how these traits are related to each other, thereby driving the processes of local adaptation and speciation. In the Australian zebra finch, we investigated whether domesticated stock, bred in captivity over tens of generations, differ in their response to a life‐history manipulation, compared to birds taken directly from the wild. In a ‘common aviary’ experiment, we thereto experimentally manipulated the environmental conditions experienced by nestlings early in life by means of a brood size manipulation, and subsequently assessed its short‐ and long‐term consequences on growth, ornamentation, immune function and reproduction. As expected, we found that early environmental conditions had a marked effect on both short‐ and long‐term morphological and life‐history traits in all birds. However, although there were pronounced differences between wild and domesticated birds with respect to the absolute expression of many of these traits, which are indicative of the different selection pressures wild and domesticated birds were exposed to in the recent past, manipulated rearing conditions affected morphology and ornamentation of wild and domesticated finches in a very similar way. This suggests that despite significant differentiation between wild and domesticated birds, selection has not altered the relationships among traits. Thus, life‐history strategies and investment trade‐offs may be relatively stable and not easily altered by selection. This is a reassuring finding in the light of the widespread use of domesticated birds in studies of life‐history evolution and sexual selection, and suggests that adaptive explanations may be legitimate when referring to captive bird studies.     

Heterosis in age‐specific selected populations of a seed beetle: Sex differences in longevity and reproductive behavior

We tested mutation accumulation hypothesis for the evolution of senescence using short‐lived and long‐lived populations of the seed‐feeding beetle, Acanthoscelides obtectus (Say), obtained by selection on early‐ and late‐life for many generations. The expected consequence of the mutation accumulation hypothesis is that in short‐lived populations, where the force of natural selection is the strongest early in life, the late‐life fitness traits should decline due to genetic drift which increases the frequency of mutations with deleterious effects in later adult stages. Since it is unlikely that identical deleterious mutations will increase in several independent populations, hybrid vigor for late‐life fitness is expected in offspring obtained in crosses among populations selected for early‐life fitness traits. We tested longevity of both sexes, female fecundity and male reproductive behavior for hybrid vigor by comparing hybrid and nonhybrid short‐lived populations. Hybrid vigor was confirmed for male virility, mating speed and copulation duration, and longevity of both sexes at late ages. In contrast to males, the results on female fecundity in short‐lived populations did not support mutation accumulation as a genetic mechanism for the evolution of this trait. Contrary to the prediction of this hypothesis, male mating ability indices and female fecundity in long‐lived populations exhibited hybrid vigor at all assayed age classes. We demonstrate that nonhybrid long‐lived populations diverged randomly regarding female and male reproductive fitness, indicating that sexually antagonistic selection, when accompanied with genetic drift for female fecundity and male virility, might be responsible for overriding natural selection in the independently evolving long‐lived populations.     

NEGATIVE FREQUENCY‐DEPENDENT SELECTION IN FEMALE COLOR POLYMORPHISM OF A DAMSELFLY

Negative frequency‐dependent selection (NFDS) is one of the most powerful selective forces maintaining genetic polymorphisms in nature. Recently many prospective cases of polymorphisms by NFDS have been reported. Some of them are very complicated, although strongly supportive of the NFDS. Here we investigate NFDS in wild populations of the dimorphic damselfly Ischnura senegalensis, in which females occur as andromorphs and gynomorphs. Specifically, we (1) test fitness responses to morph frequencies, (2) built a simple population genetic model, and (3) compare the observed and predicted morph‐frequency dynamics. Fitnesses of the two morphs are an inverse function of its own frequency in a population, and are about equal when their frequencies are similar. Thus the conditions necessary for NFDS are satisfied. The long‐term field surveys show that the morph frequencies oscillate with a period of two generations. Morph frequencies in a small population undergo large oscillations whereas those in a large population do small oscillations. The demographic properties of the observed dynamics agree well with those of our model. This example is one of the simplest confirmed cases of NFDS maintaining genetic polymorphisms in nature.     

Fine‐scale genetic structure reflects sex‐specific dispersal strategies in a population of sociable weavers (Philetairus socius)

Dispersal is a critical driver of gene flow, with important consequences for population genetic structure, social interactions and other biological processes. Limited dispersal may result in kin‐structured populations in which kin selection may operate, but it may also increase the risk of kin competition and inbreeding. Here, we use a combination of long‐term field data and molecular genetics to examine dispersal patterns and their consequences for the population genetics of a highly social bird, the sociable weaver (Philetairus socius), which exhibits cooperation at various levels of sociality from nuclear family groups to its unique communal nests. Using 20 years of data, involving capture of 6508 birds and 3151 recaptures at 48 colonies, we found that both sexes exhibit philopatry and that any dispersal occurs over relatively short distances. Dispersal is female‐biased, with females dispersing earlier, further, and to less closely related destination colonies than males. Genotyping data from 30 colonies showed that this pattern of dispersal is reflected by fine‐scale genetic structure for both sexes, revealed by isolation by distance in terms of genetic relatedness and significant genetic variance among colonies. Both relationships were stronger among males than females. Crucially, significant relatedness extended beyond the level of the colony for both sexes. Such fine‐scale population genetic structure may have played an important role in the evolution of cooperative behaviour in this species, but it may also result in a significant inbreeding risk, against which female‐biased dispersal alone is unlikely to be an effective strategy.     

Fragmentation reduces regional‐scale spatial genetic structure in a wind‐pollinated tree because genetic barriers are removed

Gene flow strongly influences the regional genetic structuring of plant populations. Seed and pollen dispersal patterns can respond differently to the increased isolation resulting from habitat fragmentation, with unpredictable consequences for gene flow and population structuring. In a recently fragmented landscape we compared the pre‐ and post‐fragmentation genetic structure of populations of a tree species where pollen and seed dispersal respond differentially to forest fragmentation generated by flooding. Castanopsis sclerophylla is wind‐pollinated, with seeds that are dispersed by gravity and rodents. Using microsatellites, we found no significant difference in genetic diversity between pre‐ and post‐fragmentation cohorts. Significant genetic structure was observed in pre‐fragmentation cohorts, due to an unknown genetic barrier that had isolated one small population. Among post‐fragmentation cohorts this genetic barrier had disappeared and genetic structure was significantly weakened. The strengths of genetic structuring were at a similar level in both cohorts, suggesting that overall gene flow of C. sclerophylla has been unchanged by fragmentation at the regional scale. Fragmentation has blocked seed dispersal among habitats, but this appears to have been compensated for by enhanced pollen dispersal, as indicated by the disappearance of a genetic barrier, probably as a result of increased wind speeds and easier pollen movement over water. Extensive pollen flow can counteract some negative effects of fragmentation and assist the long‐term persistence of small remnant populations.     

Re‐mating across years and intralineage polygyny are associated with greater than expected levels of inbreeding in wild red deer

The interaction between philopatry and nonrandom mating has important consequences for the genetic structure of populations, influencing co‐ancestry within social groups but also inbreeding. Here, using genetic paternity data, we describe mating patterns in a wild population of red deer (Cervus elaphus) which are associated with marked consequences for co‐ancestry and inbreeding in the population. Around a fifth of females mate with a male with whom they have mated previously, and further, females frequently mate with a male with whom a female relative has also mated (intralineage polygyny). Both of these phenomena occur more than expected under random mating. Using simulations, we demonstrate that temporal and spatial factors, as well as skew in male breeding success, are important in promoting both re‐mating behaviours and intralineage polygyny. However, the information modelled was not sufficient to explain the extent to which these behaviours occurred. We show that re‐mating and intralineage polygyny are associated with increased pairwise relatedness in the population and a rise in average inbreeding coefficients. In particular, the latter resulted from a correlation between male relatedness and rutting location, with related males being more likely to rut in proximity to one another. These patterns, alongside their consequences for the genetic structure of the population, have rarely been documented in wild polygynous mammals, yet they have important implications for our understanding of genetic structure, inbreeding avoidance and dispersal in such systems.     

Silver‐spoon upbringing improves early‐life fitness but promotes reproductive ageing in a wild bird

Early‐life conditions can have long‐lasting effects and organisms that experience a poor start in life are often expected to age at a faster rate. Alternatively, individuals raised in high‐quality environments can overinvest in early‐reproduction resulting in rapid ageing. Here we use a long‐term experimental manipulation of early‐life conditions in a natural population of collared flycatchers (Ficedula albicollis), to show that females raised in a low‐competition environment (artificially reduced broods) have higher early‐life reproduction but lower late‐life reproduction than females raised in high‐competition environment (artificially increased broods). Reproductive success of high‐competition females peaked in late‐life, when low‐competition females were already in steep reproductive decline and suffered from a higher mortality rate. Our results demonstrate that ‘silver‐spoon’ natal conditions increase female early‐life performance at the cost of faster reproductive ageing and increased late‐life mortality. These findings demonstrate experimentally that natal environment shapes individual variation in reproductive and actuarial ageing in nature.     

Evolution of male age‐specific reproduction under differential risks and causes of death: males pay the cost of high female fitness

Classic theories of ageing evolution predict that increased extrinsic mortality due to an environmental hazard selects for increased early reproduction, rapid ageing and short intrinsic lifespan. Conversely, emerging theory maintains that when ageing increases susceptibility to an environmental hazard, increased mortality due to this hazard can select against ageing in physiological condition and prolong intrinsic lifespan. However, evolution of slow ageing under high‐condition‐dependent mortality is expected to result from reallocation of resources to different traits and such reallocation may be hampered by sex‐specific trade‐offs. Because same life‐history trait values often have different fitness consequences in males and females, sexually antagonistic selection can preserve genetic variance for lifespan and ageing. We previously showed that increased condition‐dependent mortality caused by heat shock leads to evolution of long‐life, decelerated late‐life mortality in both sexes and increased female fecundity in the nematode, Caenorhabditis remanei. Here, we used these cryopreserved lines to show that males evolving under heat shock suffered from reduced early‐life and net reproduction, while mortality rate had no effect. Our results suggest that heat‐shock resistance and associated long‐life trade‐off with male, but not female, reproduction and therefore sexually antagonistic selection contributes to maintenance of genetic variation for lifespan and fitness in this population.     

Sex‐Biased Senescence in a Polygynous Bat Species

Bats live substantially longer than any other similar‐sized mammal despite high metabolic rates during flight. The underlying causes for the longevity of bats and the question whether bats exhibit signs of senescence – a progressive deterioration in performance – are still unclear. Here, we describe rates of senescence in individual annual fitness, survival and reproduction using survival and recruitment data collected over an 18‐yr period from 77 males and 81 females in a wild population of Saccopteryx bilineata (greater sac‐winged bat), a polygynous species inhabiting colonies where female groups are defended each by a territorial male. In individuals older than 4 yr of age, individual fitness contribution, survival and recruitment declined with increasing age in males but not in females. Rates of senescence in annual individual fitness and in reproduction of males were at least an order of magnitude higher than those of females. This finding might be explained by the ‘disposable soma theory’ that attributes senescence to an optimal allocation of resources to somatic maintenance and competing traits such as reproduction. The rate of senescence in the survival of males was also significant but of the same order of magnitude as the (non‐significant) rate of females. Unlike many other polygynous mammals, greater sac‐winged bats show little overt male–male competition. As senescence in survival was only weak in males, our results are consistent with the theories for polygynous mammals, which view the trade‐off between male investment in physical traits for intense male–male competition against survival as a major source of the decline of male survival with age. This is the first study to demonstrate sex‐specific senescence rates in a wild population of a small, long‐lived mammalian species.