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Polyandry can profoundly affect the strength of pre-copulatory sexual selection acting on males because each additional mate acquired by a female means that, all else being equal, a male's paternity share declines. However, accruing additional mates could benefit male fitness if males with greater mating success also tend to have less promiscuous females as partners. If this is indeed the case, then males should experience strong sexual selection to acquire more mates. We tested these predictions by collecting detailed mating data on male and female Cook Strait giant weta (Deinacrida rugosa) in the wild via daily radio tracking. Our sexual network-based approach indeed revealed that the most polygynous male D. rugosa mated the least polyandrous females. This finding therefore suggests that the most successful males likely face lower intensities of sperm competition and so should be selected to accrue more mates. Further, our selection analysis revealed significant pre-copulatory sexual selection on males with those having relatively smaller body size, lighter body mass, and longer legs accruing more mates than otherwise. Thus, it appears that both pre- and post-copulatory episodes of sexual selection reinforce the same male phenotype. [ABSTRACT FROM AUTHOR]

Evidence of an association between cooperative breeding systems and average coefficients of relatedness between group members in vertebrates have led to increased interest in the social and ecological factors affecting average kinship within groups. Previous studies have suggested that polygynous mating systems and high degrees of male reproductive skew increase average relatedness because they increase the proportion of offspring born in each group that are paternal siblings. Although this may be the case in semelparous organisms, in many multiparous polygynous animals, intense competition between males shortens the breeding tenure of males and leads to their frequent replacement by competitors which reduces paternal relatedness and average kinship between members of multigenerational groups. Here, we explore the interaction between male reproductive skew and the frequency of turnover in breeding males and its effects on within-group relatedness. Our theoretical model shows that increases in rates of dominance turnover in polygynous systems can offset the positive effect of male skew on relatedness between group members within seasons, showing that polygynous mating systems will not necessarily lead to significant increases in average relatedness, especially in species where there is extensive overlap between generations among group members. [ABSTRACT FROM AUTHOR]

A widely held principle in behavioral ecological research is that polygynous social systems evolve either by direct male defense of females or male defense of resources, although which of these mechanisms applies in particular species is rarely examined experimentally. We tested the relative importance of female versus resource defense in polygynous territorial male collared lizards (Crotaphytus collaris). Using a novel experimental design, we temporarily removed some of the resident females from male territories to create a female-free removal zone, whereas resident females were left intact within a non-removal zone. We then compared activity of males within each zone during three experimental phases; before we removed females, for two days when females were absent, and the day after return of females. If males defend females directly, we expected them to adjust the location of their patrol and display within removal and non-removal zones depending on the presence/absence of females, whereas we expected no such change if males defend resources. Male activity in the removal zone generally decreased when females were removed but then increased when females were replaced, whereas we observed the opposite pattern in the non-removal zone. The observed shifts in the location of patrol and display in response to the presence/absence of females, while resources remained constant, indicate that polygynous male collared lizards defend females directly. Our results suggest that male collared lizards take advantage of strong female philopatry to relatively small areas by focusing their patrol and display activities where potential mates reside. [ABSTRACT FROM AUTHOR]

Why females pair with already mated males and the mechanisms behind variation in such polygynous events within and across populations and years remain open questions. Here, we used a 19-year data set from a pied flycatcher (Ficedula hypoleuca) population to investigate, through local networks of breeding pairs, the socio-ecological factors related to the probability of being involved in a polygynous event in both sexes. Then, we examined how the breeding contexts experienced by individuals shaped the spatial and temporal separation between broods of polygamous males. The probability of polygyny decreased with the distance between nests. Indeed, secondary females were often close neighbors of primary females, although the distance between both nests increased slightly with increasing synchrony between them. The probability of polygyny was also related to the breeding time of individuals because early breeding males were more likely to become polygynous with late-breeding females. Throughout the season, there was substantial variation in the temporal separation between primary and secondary broods, and this separation was, in turn, related to the breeding asynchrony of the polygamous males (in the primary nest) relative to the neighbors. Polygynous males that bred late relative to their neighbors had a short time window to attract a second female and, thus, the breeding interval between their primary and secondary broods was reduced. Overall, the spatial proximity between polygynous males' broods and, if the opportunity existed, their temporal staggering are compatible with a male strategy to maximize paternity and reduce the costs of caring for two broods, though the effect of female's interest, either primary or secondary, cannot be fully ruled out. We highlight that a comprehensive assessment of the breeding contexts faced by individuals is essential to understand mating decisions and reconcile the discrepancies raised by previous work on social polygyny. [ABSTRACT FROM AUTHOR]

Males are often expected to benefit from mating with multiple females; however, in species where females are highly cannibalistic, achieving multiple matings may be a difficult task. When males employ strategies to avoid sexual cannibalism, it is presumed that there are benefits associated with survival--e.g. increased fitness associated with more mating opportunities. In the nursery web spider (Pisaurina mira), all males attempt to avoid sexual cannibalism by wrapping female's legs in silk prior to copulation. If males are unsuccessful, however, there are fitness benefits obtained by both sexes that are associated with their consumption--heavier and longerlived offspring. Regardless, we hypothesize that P. mira males can achieve higher fitness by avoiding sexual cannibalism. Specifically, we predict that males can and will mate with multiple females and that mating with multiple partners benefits males. To test these predictions, we conducted 1) laboratory assays to determine if males will mate with multiple females and 2) field assays to determine natural sex ratios, density, and female and male movement patterns. Finally, 3) we used our field data to construct a mathematical model that predicts natural male encounter rates with potential mates. We found that male P. mira will mate with multiple females and that increased mating numbers leads to increased offspring production. Our model suggests that under natural conditions, males have the opportunity to mate with multiple females. Overall, our findings strongly suggest that P. mira males are likely to benefit from avoiding sexual cannibalism through increased mating opportunities. [ABSTRACT FROM AUTHOR]

Although much work has analysed how individual behavioural plasticity and adaptations to ecological conditions (e.g. density, sexratio, resource distribution) shape mating systems, few studies have assessed the relative importance of multiple factors in explaining why mating systems vary from one sub-population to the next even in the same ecological conditions. Differences among groups in their phenotypic composition, such as their average phenotype, within-group variation in phenotype, or the phenotype of individuals occupying key social roles might shape the mating system emerging at the group level and explain some portion of mating system variability. Here, we take advantage of the mating system flexibility of stream water striders (Aquarius remigis) to investigate how phenotypic composition affects the mating system emerging at the group level. Groups exhibited stable mating systems varying from scramble polygyny with intense sexual conflict, to systems with a clear dominant male guarding a "harem" of females. We found that male size asymmetries and the personality of the largest individuals within groups had important effects on the group's mating system. The group's average male and female personality, size, and social plasticity also explained some of the variation in mating systems. Our study is one of the first to quantify significant relationships between group phenotypic composition and mating system variability. [ABSTRACT FROM AUTHOR]

Mating systems can vary within-species but the environmental drivers and behavioral mechanisms underlying this variation are seldom investigated experimentally. We experimentally assessed how individual behavioral plasticity in response to changes in pool and group size resulted in fundamental shifts in mating systems in water striders. We observed the same animals in larger and smaller pools, mimicking variation in pool size in natural streams, and observed a rapid, reversible change in the entire mating system. In large pools, striders exhibited scramble promiscuity with intense sexual conflict. Most males were active, harassing and driving females into hiding. Matings were frequent and typically lasted for more than 100 min. In contrast, when placed in small pools, the same animals often exhibited harem polygyny where the largest male drove other males into hiding, but allowed females to be relatively active. Matings were less frequent and of much shorter duration. Harem polygyny took several days to emerge after animals were moved to small pools, while these same animals returned to scramble promiscuity within hours after being moved to larger pools. Such variability in mating systems likely has important implications for the evolution of individual mating tactics. [ABSTRACT FROM AUTHOR]

Evolutionary theory predicts that when intrasexual competition is intense, risky behaviors can evolve if they enhance reproductive success. Here we tested the idea that polygynous males exhibit predictable variation in risk-taking during intense competition for mates. We conducted an observational study of a village weaverbird (Ploceus cucullatus) breeding colony, and video recorded synchronous fleeing events, a common predator avoidance behavior. Males adjusted their flight from the colony according to the amplitude (loudness) and Wiener entropy (harshness) of conspecific alarm calls during a perceived threat. Males also varied in how often they fled the colony. Specifically, in line with predictions based on the value of a male's territory, males with more nesting females were less likely to flee, and returned sooner if they did flee, compared to males with fewer nesting females. Males with a nest under construction also returned to their nests sooner than males without constructions in progress, consistent with predictions based on nest sabotage by conspecifics. These results suggest that male weavers perform a cost-benefit analysis in real time in order to decide how to respond to a perceived threat, with self-protection trading off with the security of one's territory and mates. [ABSTRACT FROM AUTHOR]

The distribution of resources should influence mate availability and the costs and benefits of pursuing different mating strategies. Where resources are dispersed, males may be constrained in the extent to which they can monopolize more than 1 partner, resulting in social and genetic monogamy. There is abundant correlational evidence that resource distribution influences social and mating systems, but experiments that demonstrate a causal link between these variables are relatively rare. Here, we used a replicated experiment involving 160 animals to examine how the distribution of a key resource, crevice sites used as nesting habitat, shapes social and mating behavior of a family living lizard, Liopholis whitii. The distribution of crevice sites had significant effects on several important aspects of the social and mating system. When habitat was aggregated, adults had larger home ranges and overlapped with more individuals of the opposite sex, resulting in increased opportunity for social polygyny. Aggressive female territoriality appears to impose upper limits on opportunities for polygyny by restricting female-female home range overlap. Despite this, males in aggregated habitats still formed polygynous social groups more often than males in dispersed habitat. Aggregated habitat also increased the opportunity for sexual selection, resulting in greater variance in male reproductive success and a steeper Bateman gradient compared with males occupying dispersed habitat. These effects were independent of the increase in social polygyny. Overall, our study is consistent with the hypothesis that habitat structure is fundamentally important to the evolution of social and mating systems. [ABSTRACT FROM AUTHOR]

In leks, females are often attracted to males bearing costly secondary sexual traits that are thought to honestly signal male genetic quality. The Good Genes Hypothesis predicts 1) consistent male attractiveness across a variety of environments, 2) directional selection on male attractiveness, and 3) a positive correlation between paternal attractiveness and offspring fitness. We tested these predictions in a natural population of the Italian tree frog, Hyla intermedia. We recorded the calling activity of all males at a small lek for 2 breeding seasons and we carried out an incomplete factorial breeding experiment to test for an association between paternal attractiveness and offspring fitness. Because we found no evidence for temperature-dependent genotype-by-environment interactions in calling properties, we provided evidence that male attractiveness was consistent across different thermic conditions (first prediction). Moreover, in 1 breeding season, we showed a statistically significant association between mating success and call rate, call duration, and spectral properties, suggesting that multivariate directional selection did act on these properties (second prediction). However, we found no conclusive evidence for either accepting or rejecting our third prediction. Indeed, although paternal call rate showed a marginally significant, negative correlation with offspring age at metamorphosis, the other call properties did not show any statistically significant association with offspring fitness. These results suggest that, in our study population, alternative mechanisms, such as male-male competition for signal detectability, might be a stronger driving force for the evolution of male costly displays than good genes. [ABSTRACT FROM AUTHOR]

Although ecologists and managers have been increasingly preoccupied with the crowding consequences of overabundant herbivores, the potential role of territorial behavior as a self-regulatory agent has seldom been considered. The crowding mechanism underlies most regulation models in ungulate demography and relies on the assumption of an equal share of available supplies among individuals. In contrast, in territorial systems dominant individuals monopolize resources, predicting deviations from the expected demographic outcomes under the crowding approach. We used empirical data on a protected guanaco (Lama guanicoe) population to test competing hypotheses about crowding and territorial defense as the mechanism driving density regulation in a resource-defense polygyny ungulate. We assessed density dependence on recruitment at different spatial scales and density effects on preferred forage availability. The guanaco density inside the reserve increased rapidly and then stabilized during the last third of the study period. The absence of density effects on recruitment questions the existence of crowding mechanisms. Guanaco numbers stabilized below the environmental carrying capacity predicted by an equal share of available forage, supporting territorial defense as the mechanism shaping population density in the area. Variability in forage cover was independent from changes in population density, rejecting crowding effects on food supplies. These results are consistent with the hypothesis of a self-regulatory mechanism derived from resource defense that may prevent overgrazing. Our findings suggest that other factors in addition to food availability may determine the demographic carrying capacity under resource defense systems, stressing the importance of accounting for behavioral traits when addressing management issues. [ABSTRACT FROM AUTHOR]

In scramble competition polygyny, male and female mobility may be under strong selection as a result of fitness effects of searching for reproductive resources such as mates, oviposition sites, or resources for egg production. We analyzed the relationship between mating frequency, mobility, and body size in males and females of the chrysomelid beetle Leptinotarsa undecimlineata. We obtained a detailed data set of movement and mating frequency of an entire population (1037 adults) over a full reproductive season using individual tagging and direct behavioral observations. Unlike previous studies, we found a negative relationship between mobility and mating success for both sexes. Size was positively correlated to mating frequency in females, but negatively in males. High male mobility may be the result, and not a cause, of low mating success in scramble mating polygynies where rejected or displaced males switch plants more often searching for mating opportunities. More mobile females may be looking for competition-free oviposition substrate and thus experiencing fewer sexual encounters. [ABSTRACT FROM AUTHOR]

Alternative mating tactics are common among species exhibiting resource defense polygyny. While large territorial males aggressively defend harems, small sneaker males generally invade these harems to mate furtively. The result is a sexual network that provides information on the sperm competition intensity (SCI) faced by males of both morphs. Here, we use metrics derived from the network approach to compare SCI between sneakers and territorials of the male-dimorphic harvestman Serracutisoma proximum. We also tested hypotheses about the influence of harem size and spatial distribution of harems on the SCI faced by territorial males. Sneakers faced, on average, higher levels of SCI than territorials, while the SCI faced by territorials was more variable than that of sneakers. Owners of large harems faced less intense sperm competition than owners of small harems, suggesting that sperm competition is more diluted among females in large harems. At the population level, sneakers concentrated their invasions on neighboring harems that were spatially aggregated. We argue that the spatial distribution of harems is an important element influencing the topology of the sexual network, and that the spatially explicit approach we used here can bring new insights to the study of sperm competition and mating systems in a wide range of organisms. [ABSTRACT FROM AUTHOR]

Males of polygynous mammalian species may adopt different reproductive tactics to accomplish female fertilization, with dominant males often attaining a higher reproductive success than those adopting alternative breeding tactics. We worked on the largest breeding colony of the South American fur seal to determine its mating system and quantify the breeding success of male reproductive tactics using behavioral data and paternity assignment. We sampled ~50% of reproductive males during the 2010 breeding season and 85% of pups born during the following breeding season. Paternity analyses were made with 10 microsatellite markers, and 80% (n = 36) of the candidate fathers had at least 1 offspring (mean = 2.9, range = 0–13). Paternity was determined for 47% (n = 220) of pups at 80% and 95% confidence levels. We assessed the importance of different behavioral variables (tenure, copulation, and agonistic interactions) and reproductive tactics (territorial/satellite) in South American fur seal male breeding success using generalized linear models. We used regression trees to assess the homogeneity of breeding success within each reproductive tactic. The relatively high variance in South American fur seal male breeding success and the relatively high reproductive synchrony of breeding females and their distinctive pattern of space suggest that the mating system is consistent with a lek. We found that the territorial reproductive tactic was actually composed of 3 distinct categories and that a surprisingly high proportion of territorial males had a lower breeding success than the alternative satellite male reproductive tactics. This is the first study in otariids that has assessed the breeding success of male alternative reproductive tactics.Many male mammals defend mating territories during the breeding season. Some males manage to keep their territories, whereas others, not strong enough to do so, use alternative tactics to access mates. These weaker males are not expected to be as successful in mating. However, we found this is not always true and actually sometimes their alternative tactics turned out to be the best. [ABSTRACT FROM PUBLISHER]

In lek-based mating systems only a few males are expected to obtain the majority of matings in a single breeding season and multiple mating is believed to be rare. We used 13 microsatellites to genotype greater sage-grouse (Centrocercus urophasianus) samples from 604 adults and 1206 offspring from 191 clutches (1999–2006) from Alberta, Canada, to determine paternity and polygamy (males and females mating with multiple individuals). We found that most clutches had a single father and mother, but there was evidence of multiple paternity and intraspecific nest parasitism. Annually, most males fathered only one brood, very few males fathered multiple broods, and the proportion of all sampled males in the population fathering offspring averaged 45.9%, suggesting that more males breed in Alberta than previously reported for the species. Twenty-six eggs (2.2%) could be traced to intraspecific nest parasitism and 15 of 191 clutches (7.9%) had multiple fathers. These new insights have important implications on what we know about sexual selection and the mating structure of lekking species. [ABSTRACT FROM PUBLISHER]

Among avian species with biparental care, male alternative reproductive opportunities can occur in the form of either extrapair fertilizations or additional social mates. We manipulated testosterone (T) levels in male house sparrows to assess whether participation in parental care detracts from male success in securing alternative matings; we also compared the annual reproductive success of males that engaged in normal levels of care with the success of males that displayed increased mating effort at the expense of parental care. Our results showed that the incidence of polygyny among high-T/low-parenting males was elevated relative to control males, but that success in obtaining extrapair mates was independent of hormonal treatment. Thus, male parental care seems to carry an opportunity cost in terms of reduced acquisition of additional social mates. Despite this cost, between-treatment comparisons of the estimated number of fledglings sired annually suggest that, in this species, the value of male contributions to care is sufficiently high to favor the reductions in T that facilitate normal male parenting. [ABSTRACT FROM PUBLISHER]

Serracutisoma proximum is a harvestman with alternative male morphs. Large males use sexually dimorphic second legs in fights for the possession of territories on the vegetation, where females oviposit. Small males have short second legs and do not fight but rather sneak into the territories and copulate with egg-guarding females. We investigated the presence of male dimorphism across 10 populations of S. proximum, compared gonadal investment between male morphs, and assessed if the distribution of the sneakers is influenced by harem size. In all populations, there was male dimorphism, indicated by the bimodal distribution of the leg II length/body length. Gonadal investment did not differ between morphs and was not affected by male size, second leg length, and morph relative frequency in the populations. We found 361 territories, 90.0% containing 1 male, 9.7% containing 2 males (dyads), and 0.3% containing 3 males. The probability of encountering dyads increased with the number of females present in the territories. Moreover, the proportion of sneakers in territories containing dyads was higher than would be expected by chance. One possible reason for the ubiquity of alternative morphs in S. proximum could be the high mating opportunities experienced by sneakers in spatially structured populations with a resource defense polygyny system. Additionally, the high frequency of successful invasions by sneakers and hence the high sperm competition risk for both morphs may explain the similarity in gonadal investment between male morphs. [ABSTRACT FROM PUBLISHER]

Within animal societies, the ecological and social underpinnings of mating system variation can be related to resource dispersion, sexual conflict between breeders, and the effects of non-breeders. Here, we conducted a broad-scale investigation into the evolution of mating systems in the cooperatively breeding cichlid, Neolamprologus pulcher, a species that exhibits both monogamy and polygyny within populations. Using long-term field data, we showed that polygynous groups were more spatially clustered and held by larger competitively superior males than were monogamous groups, supporting the role of resource dispersion. To explore the role of sexual conflict, we forced polygynous males to become experimentally monogamous (EM) in the field. EM males spent more time on their remaining territory than naturally polygynous males but otherwise did not change behaviorally or physiologically. Females mated to EM males performed more submissive acts, and in a forced choice experiment, females did not preferentially associate with the larger of two unmated males. Females may therefore incur an unexpected cost from mating monogamously with a large and competitively superior male, a cost that mitigates sexual conflict over the mating system. Helpers were more closely related in monogamous groups but did not behave differently under monogamy or polygyny. Helpers therefore seem neither to be affected by nor affect the mating system of breeders. Our results demonstrate the roles of resource availability and conflict mitigation in determining the mating system, and highlight the importance of experimental manipulation for revealing hidden costs of hypothetical mating patterns. [ABSTRACT FROM PUBLISHER]

I examined why anemonefishes, Amphiprion ocellaris, Amphiprion frenatus, and Amphiprion perideraion, which inhabit single host anemones, are monogamous and protandrous. Because they live in small groups (≤6 individuals) with a size hierarchy, they might have the environmental potential for polygyny. If the dominant fish were male, he could monopolize mating opportunities, and subordinates should be female. Female fecundity increases with body size, so that group body size composition largely influences his reproductive success. First, I developed an optimization model to predict the body size composition based on the carrying capacity of the host (C) and a fixed body size ratio (γ) or difference (δ) between individuals adjacent in rank. The γ and δ were assumed to be necessary for subordinates to avoid fatal eviction from the group. The model using δ and C could predict the body size composition of the 3 species. Next, I incorporated nonlinear female fecundity functions into the model to evaluate whether polygyny or monogamy was the better mating system for the dominant fish. I examined relationships between gonad weight and body size of A. frenatus and A. perideraion to estimate the functions. Assuming large δs and the nonlinear functions, dominant fish could have higher reproductive success in monogamous mating systems. The model also indicated that where C is limited, a larger δ resulted in one large, one small, and several very small subordinate individuals. This combination of body size composition model and nonlinear female fecundity functions can explain the function of protandry and monogamy under limited shelter space. [ABSTRACT FROM PUBLISHER]

Systematic deviations in sex ratio may be adaptive in the face of the prevailing environmental or physiological cues experienced by the mother; yet some theoretical and mechanistic hypotheses remain at odds and are rarely examined noninvasively under natural conditions. Conventional interpretations of the Trivers and Willard (Trivers RL, Willard DE. 1973. Natural selection of parental ability to vary the sex ratio of offspring. Science 179:90–92) hypothesis (TWH) predict that higher stress should be associated with female-biased litters; yet, several mechanistic hypotheses predict the opposite. We tested the predictions of the TWH and 2 stress-related mechanistic hypotheses in a free-living polygynandrous sciurid, Richardson’s ground squirrel, Urocitellus richardsonii. We examined the relationship between litter sex ratio and indicators of maternal condition and investment. These included litter size, juvenile mass at emergence, as well as maternal age, changes in maternal body mass, and maternal fecal glucocorticoid (cortisol and corticosterone) levels during gestation, lactation, and post-weaning. Males born of small litters were significantly heavier at emergence than males from larger litters, which were female biased, whereas females showed no significant change in mass with litter size. Mothers with higher fecal cortisol levels during the gestation period (but not during lactation or post-weaning) were more likely to produce male-biased litters, whereas females producing larger litters showed significantly higher cortisol levels during lactation (but not gestation or post-weaning) than mothers producing smaller litters. Our results provide support for both the proximate glucose-mediated mechanistic model of Cameron (Cameron EZ. 2004. Facultative adjustment of mammalian sex ratios in support of the Trivers-Willard hypothesis: evidence for a mechanism. Proc R Soc Ser B Biol Sci. 271:1723–1728) and the broad-sense TWH, where social and life-history characteristics play an integral role. [ABSTRACT FROM AUTHOR]

We explored the effects of multiple mates on male reproductive success in a species with male parental care in which an increase in the number of female mating partners does not increase the number of eggs received. The broad-nosed pipefish (Syngnathus typhle) has a polygynandrous mating system. In this species, the male cares for embryos in a specially developed brood pouch. During brooding, some embryos fail to develop. We experimentally mated males with either one or two females while keeping brood size similar. We found that broods of singly mated males showed significantly lower embryo survival than those of doubly mated males. Furthermore, larger broods showed relatively lower levels of embryo survivorship independent of number of mates. We conclude that embryo survival is affected by postcopulatory processes that appear to result in higher fitness of multiply mated males. We discuss our results in the light of parental care, sibling competition, genetic benefits, and kin selection. [ABSTRACT FROM PUBLISHER]

The theory of sexual selection predicts a relationship between male sexual traits and reproductive success. This prediction has been tested extensively using the complexity of birdsong as a model for trait elaboration. However, contradictory results have emerged. Some studies have demonstrated that males with large repertoires enjoy a reproductive advantage, whereas other studies have failed to support this prediction. To make general inferences from this mixed evidence, we quantitatively reviewed the relevant literature using a meta-analytic approach. The mean effect size for the song/mating success association was significant, but the effects were generally weak, affected by publication bias, confounded by uncontrolled variables, and differing across the traits examined. Effect sizes were heterogeneous across studies due to species-specific effects, differences in mating systems, and song phenotypes. The degree of association between song complexity and reproductive success was independent of the strength of sexual selection, as assessed by the degree of polygyny and extrapair paternity. Our results highlight the importance of considering various biological factors to understand the role of repertoires in mediating mating success in different species. [ABSTRACT FROM PUBLISHER]

Spatial distribution can be affected by sexual selection, particularly in mating systems where males have exaggerated traits used to compete for access to females. Although it is rare to be able to disentangle selection arising from male competition versus female choice in such mating systems, we here report experiments in which we manipulated group size and sex ratio to determine the relative roles of males and females in a harem polygyny. Megalorchestia californiana is an amphipod (family Talitridae) that is sexually dimorphic—males are not only larger than females but also possess enlarged red antennae and gnathopods that are used to hold and guard females prior to mating inside their burrows. We conducted 2 main types of experiments: 1) we varied the mobility of 3 amphipods (2M/1F) to determine the relative roles of male competition and female choice and 2) we monitored groups of 9 or more individuals to determine how intersexual and intrasexual interactions affect overall spatial distribution. In our 3-amphipod tests, we found that male competition was more important than female choice in explaining burrow preferences. Our large group experiments, however, indicated that females also play an active role in mate selection, as females settled in random locations in single-sex groups, whereas females clustered around larger males in mixed-sex groups. Finally, we found that male body mass was correlated with the length and redness of the antennae, which suggests that males may signal their quality through visual communication. [ABSTRACT FROM PUBLISHER]

In a polygynous mating system, females settling with already mated males often experience low mating success due to the reduced parental contribution of the male. However, there are numerous factors that may still make it advantageous for some females to choose this mating status. Facultative polygyny is believed to be dominated by male advertisement and female choice. Although quality differences and competition among females are increasingly recognized as important determinants of polygynous settlement patterns, the importance of signals of female quality in this mating system is largely unknown. Here we examined the relationship of the white wing patch size (WPS) of female collared flycatchers, a phenotypically plastic and age-dependent ornament, with social mating status, while controlling for settlement date and age. At the population level, monogamous, primary, and secondary females did not differ in WPS. However, the primary female of individual males was more ornamented than the secondary female, and this difference declined with increasing distance between primary and secondary nests. Secondary female ornamentation increased, whereas that of the primary female did not change with nest distance. These results suggest a subtle role for female ornamentation at polygynous mating. Future studies should therefore take into account mating status when assessing the costs and benefits of female signals. Moreover, patterns in quality-indicating female traits may contribute to the explanation of differences in reproductive success among females of different mating status. [ABSTRACT FROM PUBLISHER]

Social insects exhibit a great variability in their social organization, and this affects colony kin structure, relatedness among nest mates, and population genetic structure. In the mosaic of arboreal ants of neotropical habitats, mutually exclusive dominant ant species occupy different territories, and their nest distribution is spatially aggregated in patches influencing patterns of population genetic structure. In this study, we performed an analysis of the population and colony genetic structure of the facultative polygynous ant Ectatomma tuberculatum to investigate how the particular breeding and social system of this species can explain its ecological dominance in the mosaic. Within-nest genetic analysis revealed that relatedness between nest mate workers was significantly greater than zero (r = 0.30) with an effective number of queens per nest of Ne = 2.5–3, indicating that polygyny is functional in this species. Moreover, we found that queen number was highly variable, probably due to queen adoption events, leading to the prevalence of polygyny over monogyny. Finally, the strong population genetic structure and the significant isolation by distance suggested that both budding and polydomy take place in this species. The respective role of secondary polygyny, budding, and polydomy are then discussed in the context of the mosaic of arboreal ants, and we propose that this particular social organization ensures the ecological dominance of E. tuberculatum by optimizing the colonization of new available nesting sites and by increasing territory size. [ABSTRACT FROM PUBLISHER]

The polygyny threshold model states that if costs incurred are less than the benefits gained from mating polygynously in terms of breeding-situation quality, then polygyny is favored and could evolve. We constructed mathematical models and computer simulations to evaluate this hypothesis. In the basic model, there is a single locus with two alleles, which regulates whether the female is receptive to polygyny. There are two breeding situations of differing quality on which males randomly assort. Females then select a mate based on the associated breeding situation and whether the male already has mates. This basic model is extended mathematically to include a cost for the initial female of a male with multiple mates and again to include gene expression in males. The computer simulations extend the basic model to multiple loci and alleles and to multiple breeding situations. The results presented here suggest that the polygyny threshold model is valid in a population genetic context: if the fitness of females that actually mate polygynously is greater than the fitness of monogamous females on poorer breeding situations, polygyny evolves. However, this approach reveals interesting dynamics not apparent from the verbal model. If the trait is expressed in males and females, then polygyny can evolve even if females mating polygynously have a lower fitness than females mating monogamously. In the multiple breeding-situations model, the polygyny allele increases to some equilibrium value above which it experiences no selection. Surprisingly, as the cost of polygyny increases, the equilibrium frequency of the polygyny allele also increases. The difference between this evolutionary model and the ideal free distribution is discussed. [ABSTRACT FROM AUTHOR]

The rationale behind the polygyny threshold model is that the breeding situation quality (BSQ) males have to offer females varies, and that differences in BSQ offset females' costs of sharing with other females, thus favoring polygynous settling. It predicts that the first chosen territories become polygynous first, and that breeding success of secondary and contemporary monogamous females is similar. This is not generally found. Testing of the polygyny threshold model (PTM) assumes that females are equal competitors and distribute ideally free around available breeding resources, a condition probably not often met. If sharing a male is costly, and competitors differ in quality, weaker individuals should experience degrees of competitive exclusion. Setting female competitive abilities proportional to arrival order, we use an individual-based interference-competition model to examine settlement patterns. Shifts in the ratio of variance in interfemale competitiveness to interterritorial differences in BSQ result in various settlement patterns, with different predictions concerning settlement order and fitness returns. We find support for the novel predictions from data on northern lapwing (Vanellus vanellus), starling (Sturnus vulgaris), pied flycatcher (Ficedula hypoleuca), and blue tit (Parus caeruleus). We suggest that before testing polygyny predictions, an evaluation of the settlement sequence should be made, which may help to generate more accurate predictions. We argue that violation of the “equal female” assumption may explain much of the discrepancy between predictions and empirical findings in previous tests of the PTM, and that secondary females in general have lower success than do monogamous breeders because they are of lower quality. [ABSTRACT FROM AUTHOR]

Highly ornamented males are often thought to be better able to provide females with resources, parental assistance, or good genes. Individual variation in such male abilities may override the costs of polygyny and therefore largely explain within-population variation in mating patterns. We investigated the influence of variation in male ornamentation and the environment on the costs of polygyny for female collared flycatchers (Ficedula albicollis), using data from a long-term study involving 2733 breeding attempts over 19 years. We show that females suffer reduced reproductive success when mated polygynously but that the costs of polygyny depend on an interaction between male ornamentation and timing of breeding. Among early breeders, polygynously mated females experience higher reproductive success when mated to less ornamented males, but among late breeders, females mated polygynously to highly ornamented males were more successful. We suggest that a high effort spent on obtaining extrapair matings early in the season renders highly ornamented males less able to assist two females in caring for the young. Thus, a male's ability to simultaneously gain from extrapair matings and polygyny may be limited through direct effects on female reproductive success. Given such limitation, extrapair matings may be expected to be less frequent in species with biparental care and a high level of social polygyny. [ABSTRACT FROM AUTHOR]

Newly produced queens from monogyne (single-queen) colonies of the ant Solenopsis invicta usually initiate reproduction independently, that is, without worker assistance. However, some recently mated queens attempt to bypass this risky phase of new colony foundation by entering established nests to reproduce, although it is unclear how often these queens are successful in natural populations. We surveyed a mature monogyne population of S. invicta in both 1995 and 1996 for colonies headed by queens incapable of independent colony founding (diploid-male-producing queens) in order to estimate the frequency of colonies that are headed by queens that initiated reproduction within established nests (adopted queens). Using the frequency of diploid-male-producing queens among the recently mated queens in this population, we estimated that the overall rate of queen replacement by adopted queens is about 0.7% per colony per year. Although theory suggests that a change to a novel queen reproductive tactic could be associated with a fundamental change in social organization (queen number), this does not appear to be the case in monogyne S. invicta. However, the evolution of nest-infiltrating reproductive tactics by queens in a monogyne population and the evolution of multiple-queen societies may result from similar ecological pressures facing newly mated queens. We therefore incorporate this strategy into an existing theoretical framework that was developed to explain the evolution of alternative social organizations in ants, providing testable predictions regarding the distribution and frequency of queen adoption in other single-queen ant societies. [ABSTRACT FROM AUTHOR]

The evolution of polyandry requires an asymmetrical factor that favors more matings per breeding female than per breeding male, thus reversing Bateman's principle. Here a model is presented for the evolution of avian cooperative polyandry. The model shows that polyandry can evolve if communal breeding is initially advantageous and if increasing clutch size beyond an optimum is detrimental. The advantage of communal breeding favors the addition of more breeders (either males or females) and thus selects against breeding as single pairs (monogamy). The optimal dutch size creates the asymmetry that favors adding male breeders (polyandry) over adding female breeders (polygyny). Adding females is detrimental because females must lay eggs to reproduce and can therefore increase the clutch size of the group. On the other hand, males can reproduce by sharing paternity without increasing dutch size. It is shown that cooperative polyandry evolves either because it maximizes both male and female fitness or because polygyny and monogamy are behaviorally unstable. Data from acorn woodpeckers support the assumptions of the model and suggest that cooperative polyandry evolved because it is behaviorally more stable. The persistence of monogamy and polygyny in acorn woodpeckers (at a lower incidence than polyandry) is also examined. Polygyny in these birds represents a case of the Prisoner's Dilemma [ABSTRACT FROM AUTHOR]

The degree of polygyny is predicted to influence the strength of direct male–male competition, leading to a high variance in male lifetime reproductive success and to reproduction limited to the prime period of adulthood. Here, we explore the variance in male lifetime reproductive success and reproductive time in an anthropoid primate forming multimale–multifemale groups. Males of this species form dominance hierarchies, which are expected to skew reproduction toward few high-ranking males. At the same time, however, females mate with multiple males (polygynandry), which should limit the degree of polygyny. Using 20 years of genetic and demographic data, we calculated lifetime reproductive success for the free-ranging rhesus macaque (Macaca mulatta) population of Cayo Santiago for subjects that died naturally or reached senescence. Our results show that 1) male lifetime reproductive success was significantly skewed (range: 0–47 offspring; males reproducing below average: 62.8%; nonbreeders: 17.4%), 2) variance in male lifetime reproductive success was 5 times larger than in females, and 3) male lifetime reproductive success was more influenced by variation in fecundity (60%) than longevity (25%), suggesting that some direct male–male competition takes place. However, the opportunity for selection (i.e., standardized variance in male lifetime reproductive success) is low compared with that in other large mammal species characterized by a high degree of polygyny. Moreover, male reproductive life extended much beyond the prime period, showing that physical strength was not required to acquire mates. We conclude that rhesus macaques exhibit a moderate degree of polygyny and, therefore, low levels of direct male–male competition for fertile females, despite the fact that males form linear dominance hierarchies.Male rhesus macaques face moderate strength of direct competition for fertile mates, creating opportunity for indirect forms of competition. Using 20 years of genetic and demographic data, we show that variance in lifetime reproductive success is more pronounced in males than in females. Yet, most males reproduce in their lifetime, that surviving as long as possible increases males’ success, and that males reach high fecundity before the full development of secondary sex characteristics. [ABSTRACT FROM PUBLISHER]

We investigated sex allocation in three U.K. populations of the facultatively polygynous ant Leptothorax acervorum over 1-3 years. The first main finding was that, across sites, the population sex-investment ratio changed from significantly female biased to significantly male biased with increasing polygyny. This was consistent with workers controlling sex allocation and reacting to changes in their population-level relatedness asymmetry. It was also consistent with local resource competition due to reproduction by colony budding under polygyny.Worker control was supported by the finding that queen number had noeffect on sex allocation among polygynous colonies. The second main result was that monogynous colonies consistently produced more female-biased sex-investment ratios than polygynous colonies in one site only (Santon). The results from Santon supported both the relative relatedness asymmetry hypothesis and the idea of sex ratio compensation due to colony budding. The workers' response to their population-levelrelatedness asymmetry reinforced the case for relatedness asymmetry being influential at the colony level. The other populations could have lacked split sex ratios because polygynous colonies were either comparatively rare or common, making them behave as almost entirely monogynous (Aberfoyle) or polygynous (Roydon) populations. In Roydon, this was consistent with the inference from allozyme data that monogynous and polygynous colonies did not differ in their worker relatednessasymmetries. The final principal finding was that, of hypotheses linking the colony sex-investment ratio with sexual productivity, there was support for the constant female hypothesis but not for the constant male, cost variation, or multifaceted parental investment hypotheses. [ABSTRACT FROM AUTHOR]