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Polygynous males allocate substantial resources to sexual traits and behaviours to improve their chances of winning competitions for mates often at the cost of body maintenance. However, the degree to which males experience these trade-offs can be influenced by external conditions. Studies are needed that assess whether polygynous male resource allocation decisions about life history traits are density dependent. We tested for an influence of density on age-specific life history traits in male southern elephant seals, Mirounga leonina , using a 34-year data set collected at Marion Island. Specifically, we determine whether life history varied with density-related factors for survival, improved breeding success (measured as social status) and recruitment age. This was done by selecting linear models that tested biological hypotheses about density-dependent covariates related to competition intensity during breeding and natal conditions, while accounting for known intrinsic effects such as age and social status. Baseline mortalities were higher for males that had accumulated above average reproductive costs for their age than males with below average costs. This reproductive cost was determined by the number of females per harem relative to the population average. Thus, males likely allocated more resources to reproduction and less to body maintenance at all ages when defending and servicing relatively large harems, and this cost was compounding for males that dominated large harems at a young age. Males born in years with few pups were more likely to be dominant breeders and recruit at an earlier age than males born in years with many pups. Thus, breeding success and recruitment age likely depended on the population density experienced during early life, suggesting lasting effects of natal conditions in a long-lived animal. We show how density-dependent factors interact with intrinsic determinants of resource allocation to determine variation in polygynous male life history with long-term consequences. • Density at birth and breeding explains variation in polygynous male vital rates. • Males dominating large female harems experience greater cumulative survival costs. • Males of small natal cohorts recruit earlier and are more likely to be dominant. • Density-related resource allocation decisions have long-lasting consequences. [ABSTRACT FROM AUTHOR]

We investigated factors leading to variation in social complexity or 'social systems' among plateau pika family groups within a contiguous local population across 2 years. Plateau pikas are small, diurnal, nonhibernating, sexually monomorphic lagomorphs that occupy family home ranges on open alpine meadows on the Qinghai-Tibetan Plateau. Expression of the social organization, social structure, mating system and parental care system in plateau pikas did not follow expectations from traditional ecological or evolutionary explanations. Variability in plateau pika family group size and the transitions of group size between years allowed us to investigate potential advantages and disadvantages of group living. Evidence that group living served to protect pikas against predation was weak. Although social huddling could have minimized thermoregulatory costs during the extremely cold Tibetan winters, there was no correlation of overwinter survivorship among pika families of different sizes. There was no apparent group-living benefit with regard to foraging, and the occurrence of cohesive social families on the flat, continuous meadow contradicts the hypothesis that sociality is related to patchiness of critical resources. Cost of maintaining burrows appeared unrelated to group size. Most interactions between pikas occurred within family groups and were affiliative (99% of adult interactions; 97% of adult–juvenile interactions), and most interactions between adult males of different family groups were aggressive (96% of interactions). Matings were primarily within families (88% of copulations). Pikas also possess a complex vocal repertoire that enhanced interactions within social families. Demographic constraints associated with variable overwinter survivorship appeared to be the dominant precondition that produced a given family size and mating system type, coupled with selective dispersal by some pikas before the start of the breeding season. Paternal care enhanced juvenile survival, and thus led to an equalization of reproductive success among adults in families with different mating combinations. • Plateau pikas live in families occupying exclusive burrow systems and home ranges. • Pika family group size varied from one to five adults within and between years. • Pikas failed to adhere to conventional explanations for establishment of group size. • Pika families exhibited multiple social mating system types. • Pika families did not adhere to explanations for establishment of mating system types. [ABSTRACT FROM AUTHOR]

Following the introduction of DNA fingerprinting in the 1980s, studies have repeatedly revealed mismatches between the mating system inferred from social behaviour and the mating system revealed through genetic relationships. In this study, we examined the occurrence of extragroup paternities (EGPs) in gelada monkeys at Guassa, Ethiopia and explored how EGPs may be acquired in this species, which is conventionally considered to have a single breeding male ('leader') per social group ('unit'). We found that while leaders sired most offspring, a substantial proportion (17 of 88 offspring, 19%) were sired by extra-unit males. Offspring were more likely to be sired by extra-unit males when they were: (1) conceived in the 6 months following the start of peak rainfall (July–December) and (2) the first successful conception for a mother. Furthermore, eight of the 17 extra-unit paternities were directly or indirectly the result of a single infertile leader, indicating that infertility plays an important role in the occurrence of EGPs. Compiling published data revealed that the 19% EGP rate observed among Guassa geladas was also the median for polygynous nonhuman primates (range 0–57%, N = 5 populations), in contrast to geladas in the Simien Mountains, where EGPs are absent or rare. Thus, intraspecific variation in EGP rates in geladas encompasses much of the range described across polygynous primates more broadly. The Guassa gelada EGP rate was similar to the median rate reported for mammals. Primates generally had a lower median rate of EGPs, more similar to the median rate reported for birds. Understanding variation in EGP rates requires understanding the outcomes of competing interests of males and females within the same species, as well as how these features contribute to the evolution of social systems and influence variation in EGP rates at higher taxonomic levels. • Geladas at Guassa have higher extra-unit paternity rates than reported elsewhere. • Seasonal variation, parity and infertility influence extragroup paternity (EGP). • Polygynous primates have the highest median EGP rate. • Multimale groups better prevent EGPs but risk sharing paternity with group members. • Humans generally have low EGP rates compared to other primates. [ABSTRACT FROM AUTHOR]

Varying forms of polygyny are observed across many animal groups. In some species, a male defends a group of females from other males, and successful defence leads to greater reproductive success. This is often referred to as harem polygyny and is most observed in mammals. A female-biased sex ratio has been associated with harem polygynous species. In such populations, formation of 'harems' may be an inevitable consequence of the relative lack of available males, rather than multiple females actively choosing to mate with a subset of specific males. Although a rare mating system for insects, harem polygyny has been described in several orders, including tree wētā (Orthoptera: Anostostomatidae: Hemideina) in New Zealand. Aggregations of multiple females have been found with a single male in their diurnal roosts. We aimed to determine how the sex ratio and local density of Hemideina thoracica affected the formation of harems in laboratory conditions. 'Harems' were observed when the sex ratio was female biased, but no more than would be expected by chance arrangement of individuals, although females preferred to associate with males rather than be alone. Conversely, when the sex ratio was male biased, females preferred to be alone. The number of females associated with each male was lowest when the sex ratio was even and local density was low. However, males and females did not associate randomly: when local density was high aggregations of multiple males with multiple females were observed more often than expected by chance, suggesting that, in contrast to classic 'harem' behaviour, males accepted other males being present as long as females were also found in the roost. Additionally, females were more likely to be associated with males than in low-density conditions. Individuals in this study showed much more flexibility in their mating behaviour than what would be expected in a harem polygynous species. • Tree wētā aggregations in roosts vary depending on sex ratio and population density. • Males with larger heads are associated with more females. • Males avoid roosting with other males unless females are present in the roosts also. [ABSTRACT FROM AUTHOR]

Pair bonding (i.e. individuals showing a preference for a specific opposite-sex individual) has been demonstrated in several socially monogamous species. However, social bonds also occur in nonmonogamous species, but have received less attention. Currently, we do not know whether social bonds in monogamous pairs differ from social bonds in polygynous groups. We studied the socially flexible African striped mouse in the laboratory, conducting 3 h partner preference tests typically used to measure pair bonds in socially monogamous prairie voles, Microtus ochrogaster. In the field, striped mice typically live in polygynous groups, but socially monogamous pairs have also been observed. We compared social bonds between 12 monogamous pairs and 12 polygynous groups (1 male and 2 females). The social situation (monogamous versus polygynous) did not influence social bonds. Female striped mice showed a preference for their partner. While males spent more time in body contact with their partner, they showed a sexual preference for strange females. Polygynous males did not show a preference for one of their two females. While significant preferences for partners were found in striped mice, social preference was less strong than that reported for socially monogamous prairie voles. In summary, our results suggest that opposite-sex social bonds not only occur in monogamous species but also in species that live in polygynous groups, but that these bonds might be weaker in polygynous species. Highlights • Pair bonding has been demonstrated in several socially monogamous species. • Here we show that pair bonds also occur in the socially flexible striped mouse. • Polygynous groups did not differ from monogamous groups. • Pair bonds might be weaker in polygynous than in monogamous species. [ABSTRACT FROM AUTHOR]

Most studies examining rodent ultrasonic vocalizations (USVs) have investigated pericopulatory vocal behaviour in polygynous rodents, while vocalizations related to pair bond maintenance in monogamous rodents remain unexplored. In the monogamous California mouse, Peromyscus californicus , we used ultrasonic playbacks and post-playback social interactions to assess possible functions of USVs. We found that females responded with approach towards USVs of an unfamiliar male (bonded male from another pair) compared to a noise control, but displayed no difference in response to calls of their partner versus noise. Responsiveness to unfamiliar males does not appear to reflect an interest in extrapair copulations because during post-playback social interactions, females displayed more agonistic behaviours and fewer affiliative behaviours towards unfamiliar, sexually naïve ‘stranger’ males than towards their partners. We speculate that approach to unfamiliar male USVs instead may be related to territorial defence. We further explored associations within the data set. Interestingly, female affiliation with her partner was predicted by USV output, particularly a higher number and proportion of complex call types, produced during the male partner USV elicitation phase. Female approach towards USVs was related to syllable duration of one call type in partner USVs (not in unfamiliar USVs) but no other features, and sufficient variation exists in syllable duration to allow females to theoretically distinguish between individuals based on this measure. Similarly, while pregnancy state did not influence female social behaviour, it decreased approach to playback of partner USVs but not to that of unfamiliar USVs. Overall, our results illuminate concepts about vocal communication in monogamous rodent species with strong pair bonds and suggest that functions of USVs in rodents can extend beyond mate choice. [ABSTRACT FROM AUTHOR]

The availability and spatial distribution of reproductive resources determine female distribution, thus affecting the organization of mating systems and the intensity of sexual selection. Females of the harvestman Serracutisoma proximum lay eggs on specific plant species, which are defended by males of the large morph (majors). After oviposition, females remain inside the major's territory, forming a harem, which may be invaded by males of the small morph (minors) to sneak copulations. We experimentally manipulated the availability of the plants used as oviposition sites, and investigated how it affected the mating system of S. proximum . Our results show that females and minors moved preferentially to plots with high plant availability. Plots with high plant availability had more harems, which were established on the preferred plants. In plots with low plant availability, many females laid eggs on plants where S. proximum clutches had never been observed previously, rather than choosing to be a part of a harem on a preferred plant. Harem invasions were accomplished by both minors and majors, and the frequency of harem invasions was not influenced by plant availability. Finally, male–male competition for harems and the potential for sexual selection were also not influenced by plant availability. Female plasticity in oviposition site use probably attenuates competition among majors, allowing males with poorly developed weaponry to establish a territory and achieve copulations. Minors apparently adjust their distribution in response to harem density, but the income of minors does not increase the frequency of harem invasions in plots with high plant availability. Plasticity in the major mating tactic probably accounts for the high frequency of harem invasions, regardless of plant availability. We argue that behavioural plasticity may thus profoundly affect our ability to make predictions about the effects of oviposition site limitation on mating systems and the intensity of sexual selection in species exhibiting resource defence polygyny. [ABSTRACT FROM AUTHOR]

In resource defence polygyny, where males defend resources that females use for reproduction, the resource characteristics preferred by the two sexes are expected to match. We tested this expectation by comparing the shell characteristics preferred by males and females in the shell-brooding cichlid fish Lamprologus callipterus . In this species, males attract females by collecting and defending shells within which females breed. We added shells to males' nests and found that females were more likely to occupy large shells but made no distinction between new, smooth shells and old shells coated with mineral deposits. In contrast, when we placed additional shells adjacent to males' nests, males were more likely to retrieve shells covered in mineral deposits but showed no significant preference for large shells over small shells. Furthermore, many shells in males' nests were smaller than the smallest shell that females used for breeding. The discrepancy between male and female preferences suggests that empty shells in L. callipterus nests may have additional functions, beyond serving as breeding substrate. We discuss the possibility that shells may also be extended phenotype signals analogous to the decorations of a bower. [ABSTRACT FROM AUTHOR]

In cooperatively breeding or eusocial societies, opportunities may arise for helper individuals to gain direct fitness by reproducing. However, the extent to which helpers respond differentially, in terms of their reproductive behaviour, to the probability that reproductive opportunities will arise is not fully known. In many eusocial Hymenoptera, workers lay eggs only in queenless conditions following the death of the queen or queens. Relative to polygyny (multiple queens per colony), monogyny (single queen per colony) increases the probability that queenless conditions arise. We therefore tested the hypothesis that ant workers respond differentially to queenless conditions as a function of the probability of queenlessness. We compared worker behaviour and reproduction before and after removal of queens from monogynous and polygynous colonies of the ant Leptothorax acervorum . We found that, in queenless conditions, workers from monogynous colonies were significantly more likely to lay eggs, showed a significantly reduced latency to egg laying and laid eggs at a significantly higher rate per capita than workers from polygynous colonies. In addition, before queen removal, workers that laid eggs in queenless conditions across both monogynous and polygynous colonies performed a range of behaviours associated with reproduction at significantly higher rates than nonreproductive, control workers. These ‘future reproductive’ workers also significantly reduced their rates of brood care following queen removal. These findings show that workers under monogyny reproduce more readily in queenless conditions than workers under polygyny, and that would-be reproductive workers alter their behaviour before they experience the opportunity for future reproduction. They therefore suggest that workers adaptively modulate their reproductive behaviour as a function of the likelihood of opportunities for direct reproduction arising, and that workers' behaviour is affected by the ability to gain direct fitness even when reproduction is currently not occurring. [ABSTRACT FROM AUTHOR]

The hypothesis that obligate eusociality always evolved from ancestral states of strict lifetime monogamy implies that (1) facultatively eusocial lineages had to abandon multifemale breeding to achieve permanent morphologically differentiated castes, and (2) lineages of obligatorily eusocial insects had to independently re-evolve multifemale breeding when that served the inclusive fitness interests of nursing workers. Multiqueen nesting (eusocial polygyny) is known to be common across the ants, but rare in the corbiculate (eusocial) bees, the vespine wasps and the higher termites, but we show that this difference is mostly due to cases of obligate polygyny being restricted to the ants. This pattern is remarkably similar to the distribution of inquiline social parasites that use stealth rather than aggression to invade host colonies, which also repeatedly evolved in ants only. We explore the lineage-specific selection forces that have allowed or constrained de novo evolution of stable eusocial polygyny in Hamiltonian inclusive fitness terms. We argue that perennial life histories, male survival as stored sperm rather than as lifetime mates, and sib competition are possibly sufficient to explain the general prevalence of secondary polygyny across the obligatorily eusocial insects. We infer that obligate polygyny compromises eusocial ‘soma’ and ‘germ-line’ segregation in ways known to decrease developmental stability in metazoans, and we briefly evaluate the selection forces that reduce queen life span in highly, but probably not facultatively, polygynous species. We conclude that secondary polygyny in its obligate (ant) form resembles cooperative breeding with multiple ‘tragedy of the commons’ aspects, but in a peculiar manner because breeding females are selected to exploit the services of unmated workers rather than each other’s. This breeding system has likely been maintained in ants because it allows modular extensions of colonies in directly adjacent habitat of similar quality without the re-emergence of sexual conflicts or unproductive local competition with kin. [Copyright &y& Elsevier]

The mating system of European wool-carder bees, Anthidium manicatum, differs from that of most bees in three important aspects: females (1) are polyandrous and (2) mate continuously over the course of their reproductive life, while males (3) exhibit resource defence polygyny, that is, defend patches of food plants where copulations occur. To shed light on the evolution of this mating system we investigated male paternity using a combination of cage experiments and microsatellite genotyping of brood. We found that, although females possess a spermatheca for long-term sperm storage, most brood was fathered by males that had very recently mated with the breeding female, indicating pronounced last (or at least ‘late’) male sperm precedence. In the absence of males (male exclusion experiment) a large proportion of eggs remained unfertilized (resulting in haploid male offspring), but some diploid daughters arose from fathers that had been removed at least 11 days prior to egg laying. It appears that most A. manicatum eggs are fertilized with sperm from the bursa copulatrix, while the spermatheca serves only as a backup reservoir. This is the first demonstration of last male sperm precedence in aculeate Hymenoptera (bees, wasps, ants). We suggest that it has coevolved with ‘resource defence’ or ‘patrolling’-like male mating strategies in Hymenoptera, and with polyandry in anthidiine bees. [Copyright &y& Elsevier]

Inbreeding is generally rare in large, natural populations yet mate choice often appears to be random with respect to kinship. This suggests that the risks of inbreeding may be small because passive mechanisms of inbreeding avoidance, for example dispersal, are effective at lowering inbreeding risk. Previous theoretical and empirical studies have assumed that the risks of inbreeding are constant over an individual''s life span, but in the lek-breeding black grouse, inbreeding increases with female age. To determine whether inbreeding avoidance mechanisms are also age dependent, we generated four null models of random mate choice ranging from complete randomness to more biologically realistic mate choice criteria and compared these to 8years of data on inbreeding levels at four different female age classes. We additionally tested whether mate fidelity decreased inbreeding risk. Observed inbreeding in female age classes 1, 2 or ≥3 were not significantly different from random, but was approximately 3.5 times higher in female age class ≥4. Alternative models using mate choice criteria showed no significant differences between observed and expected levels for any age class. Our results are in line with previous studies on noncooperatively breeding passerine birds, which indicate that mating is random with respect to kinship and that increased inbreeding in older females can be explained by reduced male availability caused by restrictive mate choice criteria. We also found that individuals that switched mates significantly increased relatedness to partners suggesting that mate fidelity may have evolved as an important passive inbreeding avoidance mechanism. [Copyright &y& Elsevier]

In polygynous systems, female aggregation may affect the degree of polygyny by increasing the variance in male mating success. However, other population features such as the sex ratio and the age structure of males may also affect the distribution of male mating success. We combined behavioural observations and genetic data to investigate the relationship between spatial distribution, population structure and degree of polygyny in 30 red deer, Cervus elaphus, populations in Spain. We found that although female aggregation was positively related to mean harem size, under conditions of high female aggregation males were unable to monopolize whole female groups. The relationships between female aggregation and behavioural estimates of the variance in male mating success were strongly influenced by the sex ratio and the proportion of competitive males in the population. Potential skew of male mating success and potential opportunity for sexual selection were higher in adults than in young or subadult males. Finally, the behaviourally estimated distribution of male mating success matched the genetically estimated degree of polygyny, especially under conditions of relatively high synchrony in female receptivity. Our results show how population structure can interact with female aggregation in space and time to influence the opportunity for sexual selection in red deer. [ABSTRACT FROM AUTHOR]

Theory predicts that males that provide little or no parental investment can increase their reproductive success by fertilizing as many females as possible. By contrast, low male mating rate is often related to a large investment in a single mating. This view is challenged, however, by the occurrence of species in which males achieve only one or a few matings, yet invest little in mate guarding or paternity assurance. An explanation of this requires knowledge of the ecological factors affecting the mating system. When there is a female-biased sex ratio and a low probability of a female mating with additional males, the benefits of paternity protection are reduced. Under these conditions males are expected to search actively for females and invest little in each mating to maximize their mating rate. We investigated the influence of the sex ratio and male mortality on the male mate search strategy of the desert spider Stegodyphus lineatus (Eresidae), by following marked males in their natural habitat over the entire mating season. Males searching for mates suffered high mortality but encountered multiple females. During the mating season the sex ratio was highly female biased and females mated on average with a single male in their lifetime. We conclude that high costs of male mate search together with a female-biased sex ratio reduce the likelihood of multiple mating per female and the chances of male–male competition. Under these conditions males should invest in searching for more females and increasing their encounter rate. [Copyright &y& Elsevier]

Polygyny is a widespread and evolutionarily significant mating system in vertebrates. The southern elephant seal, Mirounga leonina, has often been cited as being extremely polygynous, thus providing an important reference point for studies on mating systems. During the breeding season, these animals form terrestrial harems in which one dominant male controls tens to hundreds of females. Our current understanding of polygynous mating systems seems to imply that, unlike males, females are not under selection pressure to adopt alternative mating strategies, and in the case of the southern elephant seal, the possibility of mating at sea has not been considered. Furthermore, elephant seal females are thought to breed annually. Using a 25-year mark–recapture data set, we found that elephant seal females skipped breeding seasons, often returning to pup in the following breeding season. Females did not need to haul out on land in order to breed in the following season, thus providing evidence for mating at sea by virgin and multiparous females. Nonpolygynous, opportunistic mating at sea could be an important alternative mating strategy in a supposedly strictly polygynous species. This has implications for our understanding of elephant seal ecology, demography and behaviour and of the evolution of vertebrate polygyny in general. If polygyny does not preclude females from adopting alternative mating strategies, the term ‘polygyny’ may be misleading. Traditional concentration on male strategies has hampered our understanding of mating systems, in assuming that females capitulate to these strategies. We suggest similar misinterpretations could occur in other polygynous species. [Copyright &y& Elsevier]

Although environmental conditions and biotic interactions are widely recognized as key sources of variation in circadian activity rhythms of a broad array of vertebrates, information on their actual significance outside experimental settings remains scarce. We investigated changes in circadian activity rhythms of free-ranging Cabrera voles, Microtus cabrerae, and water voles, Arvicola sapidus, in highly seasonal Mediterranean environments, and analysed how such changes were further affected by intersexual and interspecific interactions. Cabrera voles were largely diurnal, with a unimodal peak around midday during the wet season, whereas during the dry season activity was reduced during the hot midday period and increased strongly at dawn and dusk. Water voles also had a marked bimodal crepuscular pattern during the dry season, but this was much attenuated during the wet season, when they were comparatively more diurnal. Activity patterns varied little between the sexes, although with a tendency for higher overall activity by male Cabrera voles (dry season only) and water voles, possibly because of intersexual interactions involving seasonal shifts from monogamy to facultative polygyny in Cabrera voles, and year-round polygyny in water vole. Within each season, Cabrera voles appeared to change their activity patterns in the presence of water voles, reducing overall activity and shifting activity peaks towards diurnal (dry season) or crepuscular (wet season) time periods less used by water voles. Overall, this study provides evidence for the strong role of seasonal changes in environmental conditions and interspecific interactions in driving variation in the activity patterns of Mediterranean voles under natural conditions. [ABSTRACT FROM AUTHOR]

The evolution of female ornaments in species with a female-biased operational sex ratio (OSR) and intense female competition is well understood. In contrast, the adaptive value of female ornaments in species with a male-biased OSR and male competition remains largely unresolved. Mutual mate choice is one proposed explanation for the evolution of ornaments expressed in both males and females, a hypothesis supported by the increasing empirical evidence of mutual mate choice in species with a male-biased OSR. None the less, the evolution of female ornaments remains constrained, as investment in ornaments may detract from any direct benefits being signalled to males and females may fail to reap benefits sufficient to outweigh the costs of signalling. We used phenotypic engineering (i.e. manipulation of ornament size) to ask whether both sexes show a preference for sexually homologous ornaments in the polygynous mosquito, Sabethes cyaneus. We found a directional male preference for ornamented females, but no female preference for ornamented males. There was no evidence of assortative mating based on ornament size. We discuss these results within the framework of current sexual selection theory, addressing implications for both the evolution of male mate choice and the evolution of female ornaments. [Copyright &y& Elsevier]

A widespread pattern across polygynous ungulate species, and many other vertebrate taxa, is for animals of the same species to live in spatially segregated single-sex groups outside the mating season. This type of social organization is known as sexual segregation. Many hypotheses have been proposed to explain sexual segregation but there is still no agreement as to the main cause. Since this behaviour is common in polygynous ungulate species, we hypothesized that sexual segregation evolved in response to the development of male competitive mating skills. To formalize this hypothesis, we developed an individual-based evolutionary model. In this model individuals interact to gain resources and social fighting skills, which ultimately determine their reproductive success. Individuals influence their social interactions by preferring to interact with a particular ‘body size class’ of individuals. This preference is a heritable trait. Robust social preferences evolve which produce significant levels of sexual segregation over a wide range of parameters. Segregation is particularly strong when the marginal fitness of fighting skills exceeds a certain threshold. The results are qualitatively consistent with independent comparative studies, although formal validation will require carefully designed experiments. This suggests a linkage between the evolution of sexual segregation and sexual dimorphism in ungulates. To our knowledge, this is the first time that an evolutionary model has shown that sexual selection of fighting skills can drive sexual segregation in polygynous ungulates. [Copyright &y& Elsevier]

Homosexual behaviour occurs in over 130 species of birds, yet explaining its maintenance in evolutionary terms appears problematic at face value, as such sexual behaviours do not seem in immediate pursuit of reproductive goals. Parental care sexual conflict theory predicts that release from parental care translates to an increased propensity towards polygamous sexual behaviour. We hypothesized that homosexual behaviour(s) may be expected to increase in frequency for the sex that invests less in parental care and potentially enjoys increased mating opportunities. Consistent with our predictions, lower relative contribution to parental care for a particular sex is related to increased frequency of occurrence of homosexual behaviour. For males, highly polygynous species with minimal male parental investment exhibit higher frequencies of male homosexual behaviour, including male–male mounting and especially courtship. In socially monogamous species, male parental investment is greater, and the expression of male homosexual behaviour is lower. Similarly, among pair-bonding species, frequencies of male–male pair bonding increase with decreases in male contribution to care relative to females. When females of socially monogamous species provide less care than males, they exhibit higher frequencies of homosexual behaviour, namely pair bonding and courtship activities. Conversely, when females of polygynous species provide the bulk of parental care, female–female sexual behaviour is infrequently expressed. Homosexual behaviour in birds is more likely to occur under scenarios of enhanced mating opportunity without necessarily influencing reproductive success and thus may exist neutrally, or alternatively provide a behavioural template co-opted for adaptive design. [ABSTRACT FROM AUTHOR]

Many animals display multiple signals that can be used by conspecifics to gather information about the condition or quality of potential mates or competitors. Different signals can indicate different aspects of individual quality or function in spatially or temporally separated periods. However, for long-distance migratory birds, it is unclear if signals, such as plumage traits, function in different phases of the annual cycle. We investigated the potential role of carotenoid-based tail and flank plumage, and bib size, in relation to extrapair paternity and polygyny in the American redstart, Setophaga ruticilla. This work complements our previous research suggesting tail feather brightness acts as a status signal, mediating territory acquisition during the nonbreeding season in Jamaica. Here, we show that tail feather brightness also serves as an important signal during the breeding season. Specifically, our results indicate that polygyny, a behaviour highly dependent on obtaining and defending multiple territories, is significantly predicted by tail brightness. Interestingly, flank redness best predicted whether individuals secured paternity at their nest and the proportion of within-pair offspring sired. We suggest that by expanding the study of plumage function in long-distance migrants to events occurring throughout the annual cycle, we gain a critical perspective on the function and evolution of ornamental traits. [Copyright &y& Elsevier]

Polygyny is widely thought to be the dominant mating system in mammals. However, more recent genetic work casts doubt on this view. Variation in mating systems has been found in both males and females within and across mammalian species. The causes and consequences of mating system variation have important implications for understanding the population and evolutionary dynamics of species. To better understand mating system variation, both in mammals and more generally, this study analyses genetic mating system variation in dusky-footed woodrats, Neotoma fuscipes. Contrary to expectation, there was little support for polygyny at the genetic level. Instead, the study populations were characterized by promiscuity and monogamy, in both males and females. At higher densities, variance in the numbers of mates and offspring were higher in breeding males than in females, as is often observed. However, this trend was reversed in low-density, coniferous forest habitat. Model selection revealed that the best model of successfully mated pairs includes population density, operational sex ratio and individual pairwise distances as predictors. Higher densities coupled with male-biased sex ratios appear to decrease the probability of mating and decrease opportunities for polygamy, particularly in females. Although woodrats display sexual size dimorphism, male body size had no detectable effect on mating success. This study questions the prevalence of polygyny in mammals and demonstrates the need for more detailed, genetic investigations of mating systems. Future studies are needed to explore the complex interactions among mating system determinants and test hypotheses of sex-specific mating system variation. [Copyright &y& Elsevier]

Polygyny is regarded as a beneficial strategy for males, whereas females mated with polygynous males (males simultaneously paired to more than one female) often suffer a reduction in pair male contributions. This study examined the costs and benefits associated with polygyny in the cooperatively breeding cichlid Neolamprologus pulcher. In this species, males are facultatively polygynous; some males hold only one territory with one breeding female whereas other males hold multiple territories, each with its own breeding female. Polygynous males were larger than monogamous males and body-scraped less, a behaviour often associated with ectoparasite loads. Polygynous males also had larger testes (controlling for body mass) and higher circulating 11-ketotestosterone levels than monogamous males. Paradoxically, monogamous males occupied higher-quality territories with more shelter and fewer predators. Monogamous males also provided more parental care than polygynous males but the number and survival of young did not vary according to male mating behaviour. The results of our study suggest that females trade-off between male genetic quality and resources in N. pulcher. Our results imply that males holding only one territory may provide their mates with significant assets but may not be able to outcompete neighbours for additional breeding positions because of their small body size and possible higher parasite load. The lack of differences between monogamous and polygynous groups in terms of offspring survival (a measure of reproductive success) suggests that there may be few if any fitness consequences of polygynous pairing for females. [Copyright &y& Elsevier]

A key feature differentiating animal societies is the partitioning of reproduction among breeders. We studied how reproduction is partitioned among nestmate queens of the ant Formica exsecta in laboratory colonies. In polygynous (multiple-queen) colonies, queens can increase their reproductive success by laying more eggs or by increasing the proportion of eggs that develop into reproductive individuals instead of workers. We found that reproductive skew among queens for egg production was low, but that 84% of all queens contributed exclusively to one type of brood, either males or workers (no new queens are produced in the laboratory). Furthermore, our data revealed that the degree of reproductive specialization among queens significantly increased during brood development. Contrary to predictions of most reproductive skew models, the extent of reproductive skew was not associated with relatedness among co-breeding queens. We also found no association between the pattern of queen specialization and relatedness between queens and their mates. Such an association would occur if queens mated to related males specialize in male production to avoid the cost of inbreeding. Altogether, our findings show a yet undescribed pattern of reproductive specialization among nestmate queens in ants and emphasizes the need to investigate reproductive contributions of queens for each type of offspring separately. [Copyright &y& Elsevier]

We investigated the influence of caste on nestmate discrimination in the ponerine ant Pachycondyla luteipes, where workers lack functional ovaries and are totally sterile. Both a mark-and-recapture field experiment and an introduction experiment in the laboratory revealed intermixing of both nestmate and non-nestmate workers between nests. In the laboratory experiment, conspecific workers, both nestmate and non-nestmates, were almost always accepted. Workers'' internest hostility was weak and did not correlate with the distance between nests over the geographical scale studied (<130m). However, workers responded differentially to nestmate and non-nestmate workers, grooming non-nestmates more frequently than nestmates. In contrast, non-nestmate queens were usually violently attacked by resident workers, and as a result only 30% were accepted. Nestmate queens were always accepted with no aggression. Our results indicate that P. luteipes workers have the ability to recognize nestmates but are not aggressive when the non-nestmates are sterile workers. Such caste-biased acceptance has been predicted by kin selection in relation to the avoidance of intraspecific social parasitism and regulation of queen numbers. [Copyright &y& Elsevier]

The prediction that the spatial dispersion of resources that are important to females should dictate female dispersion and male mating tactics has not been previously tested in harem-forming bats. We investigated the relation between the estimated spatial distribution of available roosts, female group size, male roost fidelity and the strength of social associations in two species of harem-forming fruit bats in the genus Cynopterus. We evaluated the daily movements of individuals and groups among roosts using radiotelemetry and roost censuses at two sites in northern peninsular Malaysia. We found a high correspondence between the distribution of roost sites, female group size and male behaviour, supporting the prediction that clumped resources would promote female aggregation and high roost fidelity in males. However, there were significant interspecific differences in the strength of male–female associations, which suggested that, where roosts are abundant and similar in quality, regardless of their spatial distribution, the potential for males to monopolize mates depends on whether females move among roosts with, or independently of, males. We propose that interspecific differences in female behaviour may be related to the costs of moving between clumped versus randomly dispersed males. [Copyright &y& Elsevier]

In polygynous species, it is unclear whether extrapair matings provide a better reproductive payoff to males than additional social mates. Male house wrens, Troglodytes aedon, show three types of social mating behaviour: single-brooded monogamy, sequential monogamy (two broods) and polygyny. Thus, male reproductive success can vary depending on the number of mates, the number of broods and the number of extrapair fertilizations. We used microsatellite markers to determine the realized reproductive success (total number of young sired from both within-pair and extrapair fertilizations) of males in these three categories. We found that polygynous males were more likely to be cuckolded than monogamous males; however, half of the polygynous males had a third brood, which resulted in similar reproductive success for sequentially monogamous and polygynous males. Despite the paternity gained from extrapair fertilizations by single-brooded males, males were more successful when they produced multiple broods during a season, either sequentially (monogamy) or simultaneously (polygyny). In our population, multibrooded males were more likely to have prior breeding experience and arrived earlier in the season, which provided a better opportunity to obtain more than one brood and, thus, produce more young. [Copyright &y& Elsevier]

Sexual intimidation (sensu Smuts & Smuts 1993, Advances in the Study of Behavior, 22, 1–63) occurs when members of one sex aggressively ‘punish’ members of the other sex that refuse to mate with them or that merely associate with other individuals of the opposite sex. We examined Clutton-Brock & Parker's (1995, Animal Behaviour, 49, 1345–1365) concept that while males of many species use punishment (intimidation) to coerce females into social or even mating monogamy, such behaviour by females towards males should be rare. However, females in some species are territorial, and aggressive, and thus they may play an active role in sexual intimidation. We tested this proposition in laboratory experiments with territorial red-backed salamanders, Plethodon cinereus, that had been found as single (nonpaired) individuals and in male–female pairs (we term members of a pair ‘partners’) in the forest. We manipulated paired males such that they either had associated with another female before returning to their female partners (socially polygynous) or had not (socially monogamous). In addition, we manipulated single males such that they either had associated with another female before encountering a focal female for the first time (socially polygynous) or had not (socially naı¨ve). During the autumn courtship season, females were significantly more aggressive (threat displays and biting) towards socially polygynous partners relative to those that were socially monogamous. In addition, females spent significantly less time touching socially polygynous partners relative to socially monogamous partners. However, females that met a male for the first time did not differ significantly in their behaviour towards socially polygynous and naı¨ve males. During the late spring, females displayed no behavioural differences towards either male partners or strangers. Thus, female aggression was context dependent, with increased aggression directed only towards polygynous partners and only during the autumn. We infer that females attempt to control social polygyny by partners through aggression during the courtship season but that this coercion ceases in the spring when the females are preoccupied with searching for nest sites for brooding their eggs. [Copyright &y& Elsevier]