Photosynthetic responses of potato to Colorado potato beetle injury and differences in injury between adult males and females

Establishing rates of injury to plants and the physiological impact of this injury provides essential data in the development of economic injury levels, but variation of sex effects is not often considered. Here, we examined injury by the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), larvae and adult males and females on potato, Solanum tuberosum L. (Solanaceae). Specifically, we looked for adult sex differences between males and females in injury rates (= leaf consumption rates), and examined the impact of all types of injury (larval, adult male, and adult female) on gas exchange parameters of remaining potato leaf tissue. Experiments were conducted in the field and in growth chambers on Frito‐Lay proprietary and Pike chipping‐potato varieties at pre‐blooming and blooming stages. We found no change in photosynthetic rates on remaining (uninjured) leaf tissue infested with male, female, or fourth‐stage larva of Colorado potato beetle. However, when the midrib was cut in trials with male beetles, the remaining tissue above the injury exhibited photosynthetic rate reductions as a result of stomatal limitations. These findings are consistent with the pattern that we and other researchers have observed with gross tissue removal by various insects on other plant species. Adult females consumed more tissue than males, and temperature was positively correlated with feeding rates for both sexes. Sex‐related differences in feeding rate are most important to studies quantifying consumption rates for economically important species because of its potential impact on resulting economic injury level calculations.     

Female House Mice do not Differ in Their Exploratory Behaviour from Males

Dispersal is an important ecological trait affecting genetic variation and dynamics of populations. Hence, the exploratory behaviour prior to actual dispersal may be crucial for potentially dispersing individuals. In mammals, females are traditionally seen as the more philopatric sex and dispersal as male‐biased behaviour, and so behavioural strategies related to the exploration of novel resources should be differentially expressed in males and females. In addition, due to sexual selection exploratory strategies may be expected to vary according to females’ reproductive phase. We employed a standard open‐field test as an approximation of the first phase of dispersal, using adult house mice representing two subspecies, M. m. musculus and M. m. domesticus. We tested the prediction that exploration of neutral area varies in females during different phases of the oestrus cycle and is different between both sexes and subspecies. We expected to find higher exploration in males, as the more dispersing sex and less pronounced subspecies‐specific differences in females than in males. We found no significant effect of the oestrous phase on any of the parameters of the exploratory behaviour measured. Sexual dimorphism was found only in latency to enter the arena in M. m. domesticus where females hesitated longer to enter a new area than males. Significant subspecies‐specific differences were found in three of four tested exploration parameters, so we conclude that females of both subspecies follow similar strategies to those displayed by males. Musculus mice show shorter latency to enter a new area, but once inside, domesticus mice explore the arena significantly longer, with less frequent retreats to a shelter. Our results thus highlight that the role of female dispersal in interdemic gene flow should not be neglected.     

Resightings of humpback whales in Hawaiian waters over spans of 10–32 years: Site fidelity,sex ratios,calving rates,female demographics,and the dynamics of social and behavioral roles of individuals

From a database of approximately 5,000 Hawaiian humpback whales identified photographically between 1976 and 2010, we extracted 71 males and 39 females having resighting spans of 10 or more years, from first to most recent sighting. Findings included: (1) the male‐biased sex ratio was like that found in breeding grounds worldwide; (2) the mean span for males of 20.7 yr (maximum = 32 yr) did not differ significantly from the mean of 19.8 yr (maximum = 29 yr) for females, but males were seen in significantly more years during their spans than were females; (3) the mean number of females seen with and without calf across 11 three‐year intervals from 1977 to 2009 did not differ significantly; (4) the calving rate for the 39 females was 0.48 and seven females produced two to eight calves over spans of 22–26 yr; (5) females attracted significantly more escorts in years without calf than in years with calf; (6) individuals showed great diversity in the social units they occupied over their sighting spans, but with the most frequently observed unit for both sexes being the trio of mother, calf, and escort. Males were also observed frequently in competitive groups centered about a female without calf.     

Genomic pedigree reconstruction identifies predictors of mating and reproductive success in an invasive vertebrate

The persistence of an invasive species is influenced by its reproductive ecology, and a successful control program must operate on this premise. However, the reproductive ecology of invasive species may be enigmatic due to factors that also limit their management, such as cryptic coloration and behavior. We explored the mating and reproductive ecology of the invasive Brown Treesnake (BTS: Boiga irregularis) by reconstructing a multigenerational genomic pedigree based on 654 single nucleotide polymorphisms for a geographically closed population established in 2004 on Guam (N = 426). The pedigree allowed annual estimates of individual mating and reproductive success to be inferred for snakes in the study population over a 14‐year period. We then employed generalized linear mixed models to gauge how well phenotypic and genomic data could predict sex‐specific annual mating and reproductive success. Average snout–vent length (SVL), average body condition index (BCI), and trappability were significantly related to annual mating success for males, with average SVL also related to annual mating success for females. Male and female annual reproductive success was positively affected by SVL, BCI, and trappability. Surprisingly, the degree to which individuals were inbred had no effect on annual mating or reproductive success. When juxtaposed with current control methods, these results indicate that baited traps, a common interdiction tool, may target fecund BTS in some regards but not others. Our study emphasizes the importance of reproductive ecology as a focus for improving BTS control and promotes genomic pedigree reconstruction for such an endeavor in this invasive species and others.     

Mate and territory availability affect breeding dispersal and divorce in a resident Southern House Wren Troglodytes aedon musculus population

Breeding dispersal is the movement of an individual between breeding attempts and is usually associated with the disruption of the social pair bond, although mates may disperse together as a social unit. In monogamous territorial species, the decision to disperse may be affected by individual attributes such as sex, age and condition of the disperser. However, environmental and social contexts may also play a crucial role in the decision to disperse. We analysed capture‐resighting data collected over 9 years to study breeding dispersal and divorce rates of a Southern House Wren Troglodytes aedon musculus population in South Temperate Argentina. Between‐season dispersal was more frequent than within‐season dispersal, with females dispersing more often than males, both between and within seasons. Both within‐season and between‐season breeding dispersal probability was affected by territory availability, but not by previous breeding success. When the adult sex ratio (ASR) was more skewed towards males, male between‐season dispersal was also affected by mating status, with widowed and single males dispersing more often than paired males. Within‐season divorce increased the reproductive success of females but not males, and was affected by the availability of social partners (with increasingly male‐skewed ASR). Our results suggest that territorial vacancies and mating opportunities affect dispersal and divorce rates in resident Southern House Wrens, highlighting the importance of social and environmental contexts for dispersal behaviour and the stability of social pair bonds.     

Shoal sex composition affects exploration in the Mediterranean killifish

As a consequence of sexual selection, males and females may exhibit wide behavioural differences, for example, spatial behaviour. In fish, the two sexes often show different exploratory tendencies. This sex difference has been usually studied by testing individual fish. As many fish species live in social groups with different sex composition, the aforementioned approach might not picture the natural variation of the exploratory behaviour expressed by males and females. Here, we observed shoals of four Mediterranean killifish, Aphanius fasciatus, with three different sex compositions (4 females, 4 males, or 2 females and 2 males) during the exploration of a novel environment. Sex composition of the shoals did not predict the latency to emerge from a shelter into the novel environment. However, once emerged, shoals composed by four males displayed reduced exploratory behaviour compared to 4‐female and mixed‐sex shoals. These results indicated that sex differences in exploration subsist also at group level and highlighted the importance of sex composition in determining the behaviour of the entire shoal.     

Sex differences in leucocyte telomere length in a free‐living mammal

Mounting evidence suggests that average telomere length reflects previous stress and predicts subsequent survival across vertebrate species. In humans, leucocyte telomere length (LTL) is consistently shorter during adulthood in males than in females, although the causes of this sex difference and its generality to other mammals remain unknown. Here, we measured LTL in a cross‐sectional sample of free‐living Soay sheep and found shorter telomeres in males than in females in later adulthood (>3 years of age), but not in early life. This observation was not related to sex differences in growth or parasite burden, but we did find evidence for reduced LTL associated with increased horn growth in early life in males. Variation in LTL was independent of variation in the proportions of different leucocyte cell types, which are known to differ in telomere length. Our results provide the first evidence of sex differences in LTL from a wild mammal, but longitudinal studies are now required to determine whether telomere attrition rates or selective disappearance are responsible for these observed differences.     

Annual variability in dentin δ15N and δ13C reveal sex differences in weaning age and feeding habits in Risso's dolphins (Grampus griseus)

Teeth of odontocetes accumulate annual dentinal growth layer groups (GLGs) that record isotope ratios, which reflect the time of their synthesis. Collectively, they provide lifetime records of individual feeding patterns from which life history traits can be inferred. We subsampled the prenatal dentin and postnatal GLGs in Risso's dolphins (Grampus griseus) (n = 65) that stranded or were collected as bycatch in Taiwan (1994–2014) and analyzed them for δ¹⁵N and δ¹³C. Age‐specific δ¹⁵N and δ¹³C values were corrected for effects of calendar year, stranding site, C/N, and sex. δ¹⁵N values were higher in prenatal layers (14.94‰ ± 0.74‰) than in adult female GLGs (12.58‰ ± 0.20‰), suggesting fetal enrichment during gestation. Decreasing δ¹⁵N values in early GLGs suggested changes in dietary protein sources during transition to complete weaning. Weaning age was earlier in males (1.09 yr) than in females (1.81 yr). Significant differences in δ¹⁵N values between weaned males and females suggest potential sexual segregation in feeding habits. δ¹³C values increased from the prenatal to the 4th GLG by ~1.0‰, indicative of a diet shift from ¹³C‐depleted milk to prey items. Our results provide novel insights into the sex‐specific ontogenetic changes in feeding patterns and some life history traits of Risso's dolphins.     

Within‐female plasticity in sex allocation is associated with a behavioural polyphenism in house wrens

Sex allocation theory assumes individual plasticity in maternal strategies, but few studies have investigated within‐individual changes across environments. In house wrens, differences between nests in the degree of hatching synchrony of eggs represent a behavioural polyphenism in females, and its expression varies with seasonal changes in the environment. Between‐nest differences in hatching asynchrony also create different environments for offspring, and sons are more strongly affected than daughters by sibling competition when hatching occurs asynchronously over several days. Here, we examined variation in hatching asynchrony and sex allocation, and its consequences for offspring fitness. The number and condition of fledglings declined seasonally, and the frequency of asynchronous hatching increased. In broods hatched asynchronously, sons, which are over‐represented in the earlier‐laid eggs, were in better condition than daughters, which are over‐represented in the later‐laid eggs. Nonetheless, asynchronous broods were more productive later within seasons. The proportion of sons in asynchronous broods increased seasonally, whereas there was a seasonal increase in the production of daughters by mothers hatching their eggs synchronously, which was characterized by within‐female changes in offspring sex and not by sex‐biased mortality. As adults, sons from asynchronous broods were in better condition and produced more broods of their own than males from synchronous broods, and both males and females from asynchronous broods had higher lifetime reproductive success than those from synchronous broods. In conclusion, hatching patterns are under maternal control, representing distinct strategies for allocating offspring within broods, and are associated with offspring sex ratios and differences in offspring reproductive success.     

Sex‐related differences in the postmolt distribution of Weddell seals (Leptonychotes weddellii) in the southern Weddell Sea

The population of Weddell seals (Leptonychotes weddellii) in the southern Weddell Sea is in a unique position on the continental shelf edge, with vast shelf waters to the south, and deep Southern Ocean to the north. We describe sex‐related differences in the winter distribution of this population, from data collected by 20 conductivity‐temperature‐depth satellite relay data loggers deployed in February 2011 at the end of the annual molt. The regional daily speed was calculated, and a state‐space model was used to estimate behavioral states to positions along individuals’ tracks. GLMMs estimated that males and smaller individuals, diving in shallower water, traveled less far per day of deployment (males 14.6 ± 2.26 km/d, females 18.9 ± 2.42 km/d), and males were estimated to dive in shallower water (males 604 ± 382 m, females 1,875 ± 1,458 m). Males and smaller individuals were also estimated to be more resident; males spent an average 83.4% ± 7.7% of their time in a resident behavioral state, compared to females at 74.1% ± 7.1%. This evidence that male and female Weddell seals in the southern Weddell Sea are adopting different strategies has not been shown elsewhere along their circumpolar distribution.     

Intensity of space use reveals conditional sex‐specific effects of prey and conspecific density on home range size

Home range (HR) size variation is often linked to resource abundance, with sex differences expected to relate to sex‐specific fitness consequences. However, studies generally fail to disentangle the effects of the two main drivers of HR size variation, food and conspecific density, and rarely consider how their relative influence change over spatiotemporal scales. We used location data from 77 Eurasian lynx (Lynx lynx) from a 16‐year Scandinavian study to examine HR sizes variation relative to prey and conspecific density at different spatiotemporal scales. By varying the isopleth parameter (intensity of use) defining the HR, we show that sex‐specific effects were conditional on the spatial scale considered. Males had larger HRs than females in all seasons. Females' total HR size declined as prey and conspecific density increased, whereas males' total HR was only affected by conspecific density. However, as the intensity of use within the HR increased (from 90% to 50% isopleth), the relationship between prey density and area showed opposing patterns for females and males; for females, the prey density effect was reduced, while for males, prey became increasingly important. Thus, prey influenced the size of key regions within male HRs, despite total HR size being independent of prey density. Males reduced their HR size during the mating season, likely to remain close to individual females in estrous. Females reduced their HR size postreproduction probably because of movement constrains imposed by dependent young. Our findings highlight the importance of simultaneously considering resources and intraspecific interactions as HR size determinants. We show that sex‐specific demands influence the importance of prey and conspecific density on space use at different spatiotemporal scales. Thus, unless a gradient of space use intensity is examined, factors not related to total HR size might be disregarded despite their importance in determining size of key regions within the HR.     

Assessing population size and structure for Andean Condor Vultur gryphus in Bolivia using a photographic ‘capture‐recapture’ method

The Andean Condor Vultur gryphus is a globally threatened and declining species. Problems of surveying Andean Condor populations using traditional survey methods are particularly acute in Bolivia, largely because only few roosts are known there. However, similar to other vulture species, Andean Condors aggregate at animal carcasses, and are individually recognizable due to unique morphological characteristics (size and shape of male crests and pattern of wing coloration). This provided us with an opportunity to use a capture‐recapture (‘sighting‐resighting’) modelling framework to estimate the size and structure of an Andean Condor population in Bolivia using photographs of individuals taken at observer‐established feeding stations. Between July and December 2014, 28 feeding stations were established in five different zones throughout the eastern Andean region of Bolivia, where perched and flying Andean Condors were photographed. Between one and 57 (mean = 20.2 ± 14.6 sd) Andean Condors were recorded visiting each feeding station and we were able to identify 456 different individuals, comprising 134 adult males, 40 sub‐adult males, 79 juvenile males, 80 adult females, 30 sub‐adult females and 93 juvenile females. Open population capture‐recapture models produced population estimates ranging from 52 ± 14 (se) individuals to 678 ± 269 individuals across the five zones, giving a total of 1388 ± 413 sd individuals, which is roughly 20% of the estimated Andean Condor global population. Future trials of this method need to consider explicitly knowledge of Andean Condor movements and home‐ranges, habitat preferences when selecting suitable sites as feeding stations, juvenile movements and other behaviours. Sighting‐resighting methods have considerable potential to increase the accuracy of surveys of Andean Condors and other bird species with unique individual morphological characteristics.     

Does breeding population trajectory and age of nesting females influence disparate nestling sex ratios in two populations of Cooper's hawks?

Offspring sex ratios at the termination of parental care should theoretically be skewed toward the less expensive sex, which in most avian species would be females, the smaller gender. Among birds, however, raptors offer an unusual dynamic because they exhibit reversed size dimorphism with females being larger than males. And thus theory would predict a preponderance of male offspring. Results for raptors and birds in general have been varied although population‐level estimates of sex ratios in avian offspring are generally at unity. Adaptive adjustment of sex ratios in avian offspring is difficult to predict perhaps in part due to a lack of life‐history details and short‐term investigations that cannot account for precision or repeatability of sex ratios across time. We conducted a novel comparative study of sex ratios in nestling Cooper's hawks (Accipiter cooperii) in two study populations across breeding generations during 11 years in Wisconsin, 2001–2011. One breeding population recently colonized metropolitan Milwaukee and exhibited rapidly increasing population growth, while the ex‐Milwaukee breeding population was stable. Following life‐history trade‐off theory and our prediction regarding this socially monogamous species in which reversed sexual size dimorphism is extreme, first‐time breeding one‐year‐old, second‐year females in both study populations produced a preponderance of the smaller and cheaper sex, males, whereas ASY (after‐second‐year), ≥2‐year‐old females in Milwaukee produced a nestling sex ratio near unity and predictably therefore a greater proportion of females compared to ASY females in ex‐Milwaukee who produced a preponderance of males. Adjustment of sex ratios in both study populations occurred at conception. Life histories and selective pressures related to breeding population trajectory in two age cohorts of nesting female Cooper's hawk likely vary, and it is possible that these differences influenced the sex ratios we documented for two age cohorts of female Cooper's hawks in Wisconsin.     

Does selection on horn length of males and females differ in protected and hunted populations of a weakly dimorphic ungulate?

Weaponry in ungulates may be costly to grow and maintain, and different selective pressures in males and females may lead to sex‐biased natural survival. Sexual differences in the relationship between weapon growth and survival may increase under anthropogenic selection through culling, for example because of trophy hunting. Selection on weaponry growth under different scenarios has been largely investigated in males of highly dimorphic ungulates, for which survival costs (either natural or hunting related) are thought to be greatest. Little is known, however, about the survival costs of weaponry in males and females of weakly dimorphic species. We collected information on horn length and age at death/shooting of 407 chamois Rupicapra rupicapra in a protected population and in two hunted populations with different hunting regimes, to explore sexual differences in the selection on early horn growth under contrasting selective pressures. We also investigated the variation of horn growth and body mass in yearling males (n = 688) and females (n = 539) culled in one of the hunted populations over 14 years. The relationship between horn growth and survival showed remarkable sexual differences under different evolutionary scenarios. Within the protected population, under natural selection, we found no significant trade‐off in either males or females. Under anthropogenic pressure, selection on early horn growth of culled individuals showed diametrically opposed sex‐biased patterns, depending on the culling regime and hunters’ preferences. Despite the selective bias between males and females in one of the hunted populations, we did not detect significant sex‐specific differences in the long‐term pattern of early growth. The relationship between early horn growth and natural survival in either sex might suggest stabilizing selection on horn size in chamois. Selection through culling can be strongly sex‐biased also in weakly dimorphic species, depending on hunters’ preferences and hunting regulations, and long‐term data are needed to reveal potential undesirable evolutionary consequences.     

Hit‐and‐run trophallaxis of small hive beetles

Some parasites of social insects are able to exploit the exchange of food between nestmates via trophallaxis, because they are chemically disguised as nestmates. However, a few parasites succeed in trophallactic solicitation although they are attacked by workers. The underlying mechanisms are not well understood. The small hive beetle (=SHB), Aethina tumida, is such a parasite of honey bee, Apis mellifera, colonies and is able to induce trophallaxis. Here, we investigate whether SHB trophallactic solicitation is innate and affected by sex and experience. We quantified characteristics of the trophallactic solicitation in SHBs from laboratory‐reared individuals that were either bee‐naïve or had 5 days experience. The data clearly show that SHB trophallactic solicitation is innate and further suggest that it can be influenced by both experience and sex. Inexperienced SHB males begged more often than any of the other groups had longer breaks than their experienced counterparts and a longer soliciting duration than both experienced SHB males and females, suggesting that they start rather slowly and gain more from experience. Successful experienced females and males were not significantly different from each other in relation to successful trophallactic interactions, but had a significantly shorter soliciting duration compared to all other groups, except successful inexperienced females. Trophallactic solicitation success, feeding duration and begging duration were not significantly affected by either SHB sex or experience, supporting the notion that these behaviors are important for survival in host colonies. Overall, success seems to be governed by quality rather than quantity of interactions, thereby probably limiting both SHB energy investment and chance of injury (<1%). Trophallactic solicitation by SHBs is a singular example for an alternative strategy to exploit insect societies without requiring chemical disguise. Hit‐and‐run trophallaxis is an attractive test system to get an insight into trophallaxis in the social insects.     

A further cost for the sicker sex? Evidence for male‐biased parasite‐induced vulnerability to predation

Males are typically the sicker sex. Data from multiple taxa indicate that they are more likely to be infected with parasites, and are less “tolerant,” or less able to mitigate the fitness costs of a given infection, than females. One cost of infection for many animals is an increased probability of being captured by a predator. A clear, hitherto untested, prediction is therefore that this parasite‐induced vulnerability to predation is more pronounced among males than females. We tested this prediction in the sexually size dimorphic guppy, Poecilia reticulata, in which females are typically larger than males. We either sham or experimentally infected guppies with Gyrodactylus turnbulli, elicited their escape response using an established protocol and measured the distance they covered during 60 ms. To discriminate between the effects of body size and those of other inherent sex differences, we size‐matched fish across treatment groups. Infection with G. turnbulli reduced the distance covered during the escape response of small adults by 20.1%, whereas that of large fish was unaffected. This result implies that parasite‐induced vulnerability to predation is male‐biased in the wild: although there was no difference in escape response between our experimentally size‐matched groups of males and females, males are significantly smaller across natural guppy populations. These results are consistent with Bateman's principle for immunity: Natural selection for larger body sizes and longevity in females seems to have resulted in the evolution of increased infection tolerance. We discuss the potential implications of sex‐ and size‐biased parasite‐induced vulnerability to predation for the evolutionary ecology of this host–parasite interaction in natural communities.     

Sex differences in vocal patterns in the northern muriqui (Brachyteles hypoxanthus)

We investigated whether sex differences in spatial dynamics correlate with rates of staccato and neigh vocalizations in northern muriquis (Brachyteles hypoxanthus) at the Reserva Particular do Patrimônio Natural–Feliciano Miguel Abdala, Minas Gerais, Brazil. A total of 2,727 10 min focal subject samples were collected on 32 adult females and 31 adult males between April 2007 and March 2008. Compared with males, females spent a significantly lower proportion of their time in proximity to other group members and gave staccatos at significantly higher rates while feeding, resting, and traveling. Conversely, males emitted neigh vocalizations at significantly higher rates than females when feeding and resting only. Both sexes gave significantly more staccatos when feeding than when they were engaged in other activities, but their respective rates of neighs did not vary across activities. Both females and males emitted staccato vocalizations at significantly higher rates during times of the year when preferred foods were scarce, but no seasonal differences in the rates of neigh vocalizations were observed in either sex. Females and males showed a reduction in the number of neighbors following staccato vocalizations and an increase in the number of neighbors following neigh vocalizations. Our findings of sex differences in the rates of staccato and neigh vocalizations and the effects of these vocalizations on interindividual spacing are consistent with sex differences in spatial dynamics, and confirm the role of vocal communication in mediating spatial associations in this species. Am. J. Primatol. 72:122–128, 2010. © 2009 Wiley‐Liss, Inc.     

Social and demographic influences on the feeding ecology of giraffe in the Luangwa Valley,Zambia: 1973–2014

Body size influences metabolic rate, which impacts feeding ecology. Body mass differs by sex in size‐dimorphic species, such as giraffes, and also by age. Giraffes reside in a fission–fusion social system, which influences feeding ecology due to frequent changes in group size and composition. We analysed 40 years of feeding records collected from a population of Thornicroft's giraffes (Giraffa camelopardalis thornicrofti) living in the Luangwa Valley, Zambia. We examined the influence of herd composition, age and sex on diet. Solitary males and herd males did not differ in diet. Dietary diversity was comparable for females and males, with sex differences in plant species eaten present during the dry season. Age differences in feeding ecology were pronounced, with juveniles often feeding on bushes and smaller trees, while adults tended to feed upon taller trees. Both sexes have evolved foraging strategies that maximize nutrient and energy intake commensurate with their reproductive strategies, with male metabolic requirements sometimes greater, and sometimes less, than that of females. We propose that females are not exchanging foraging efficiency with reproductive tactics by feeding on smaller trees in the open, but are increasing prospects for their calves to survive when confronted with interspecific competition by browsers.     

Sex differences in ageing in natural populations of vertebrates

In many long-lived vertebrates (including humans), adult males have shorter lifespans than adult females, partly as a result of higher annual rates of mortality in males and partly owing to sex differences in the rate of ageing. A probable explanation of the evolution of sex differences in ageing is that, in polygynous species, intense intrasexual competition between males restricts the number of seasons for which individual males are able to breed successfully, weakening selection pressures favouring adult longevity in males relative to females. If this is the case, sex differences in adult longevity and in the onset and rate of senescence should be greater in polygynous species than in monogamous ones and their magnitude should be related to the duration of effective breeding males compared with females. Here, we use data from longitudinal studies of vertebrates to show that reduced longevity in adult males (relative to females) is commonly associated with a more rapid decline in male than female survival with increasing age and is largely confined to polygynous species. The magnitude of sex differences in adult longevity in different species is consistently related to the magnitude of sex differences in the duration of effective breeding, calculated across surviving adults. Our results are consistent with the suggestion that sex differences in senescence in polygynous species are a consequence of weaker selection for longevity in males than females.