Degree Of Polygyny Research Articles

Reproductive Strategies Change With Time in a Newly Founded Colony of Spotless Starlings (Sturnus unicolor)

Variation in avian reproductive strategies is often studied from a comparative perspective, since even closely-related taxa differ greatly in the degree of polygyny, extra-pair paternity (EPP) or intra-specific brood-parasitism. However, substantial variation at the species level suggests that ecological factors are important in shaping these patterns. In this study, we examined the temporal plasticity of these strategies, following a population from the year of colony formation to 2 years after this. Parentage data from these years shows that polygyny decreased with time, likely as a consequence of increased competition for nesting sites and mates by new recruits, and immigrants of higher quality arriving to the colony as time passed. In parallel to this temporal change, we found an increase in intra-specific brood-parasitism and quasi-parasitism (QP). We interpret these patterns as a consequence of an increase of floaters with time; these birds pursue a mixture of alternative mating strategies to succeed in the population. We also found evidence of conspecific brood parasitism (CBP), by nesting females that laid part of the clutch in another nest or that after losing a partially laid clutch resorted to lay the last eggs in another nest. Analyses of the distance between the main nest and nests containing the secondary polygynous brood or extra-pair or parasitic young showed an avoidance of contiguous nests for conducting these alternative reproductive tactics. At the same time, these secondary nests were closer to the main nest than random distances within the colony, suggesting that access to public information was restricted to a narrow area around the main nest. Our study emphasizes how behavioral patterns are plastic traits that vary not only with individual circumstances, but also with time, tracking changes in density and social structure.

Capital-Income Breeding in Male Ungulates: Causes and Consequences of Strategy Differences Among Species

The capital and income breeding concept links energy resources used during reproduction to the timing of their acquisition. During reproduction, capital breeders rely on resources gained previously and accumulated for reproductive investment. By contrast, income breeders use mainly resources collected during the period of reproductive activity. Most commonly, this concept is applied to females; relatively few studies have considered males. Moreover, there has been little attention to the link between the capital-income divide and other aspects of mating strategy. We studied adult males of three wild ungulates with different levels of polygyny. A large dataset (4,264 red deer, 53,619 roe deer, and 13,537 Alpine chamois, respectively) was obtained during 2007–2017 in the whole territory of Slovenia and in the Trento province, Italy. During the rut, body mass loss of males in highly polygynous species was more than twice that of weakly polygynous species: on average, red deer stags lost 19.5%; chamois bucks 16.0%; and roe deer bucks 7.5% of their body mass. This indicates potential for a hitherto unrecognised link between the degree of intrasexual competition and the degree of capital mating. The variability in body mass at the end of the rut was clearly reduced in both highly polygynous species (from 15.1 to 9.4% in red deer, and from 12.5 to 10.5% in chamois), but did not change in roe deer. Finally, roe deer bucks had recovered body mass to that of the pre-rut period by just 2 months after the rut, while red deer stags did not manage to compensate the loss of weight until the end of the year. We suggest that, at least in ungulates, there is a link between the degree of polygyny and that of capital breeding. Males of capital and income breeders underwent body mass changes resulting from different reproductive investment during the rut. Capital breeders lost considerably more weight, and invested a variable amount of energy among individuals or among years, possibly to cope with different environmental or body conditions. In so doing, they ended the rut with poorer but more even condition among individuals.

Evolution of ungulate mating systems: Integrating social and environmental factors.

Ungulates exhibit diverse mating systems that range from monogamous pair territories to highly polygynous leks. We review mating systems and behaviors across ungulates and offer a new approach synthesizing how interacting factors may shape those mating systems. Variability exists in mating systems among and within species of ungulates and likely is affected by predation risk, availability of resources (food and mates), habitat structure, and sociality. Ungulate mating systems may be labile as a consequence of the varying strength of those interacting factors. In addition, degree of polygyny and sexual dimorphism in size are associated with the evolution of mating systems. Neither male–male combat nor paternal care, however, can completely explain differences in sexual size dimorphism for ungulates, a necessary component in understanding the development of some mating systems. Whatever the evolutionary pathway, sexual segregation limits paternal care allowing more intense male–male competition. Selection of habitat structure, because it modifies risk of predation, is a major determinant of sociality for ungulates. Likewise, ruggedness and steepness of terrain limit the types of mating systems that can occur because of limitations in group size and cohesiveness, as well as the ability of males to herd even small groups of females effectively. The quality and defensibility of resources affect mating systems, as does the defensibility of females. Population density of females also may be a critical determinant of the types of mating systems that develop. Size of groups likewise constrains the types of mating tactics that males can employ. Our aim was to use those relationships to create a broad conceptual model that predicts how various environmental and social factors interact to structure mating systems in ungulates. This model provides a useful framework for future tests of the roles of both ecological and social conditions in influencing the social systems of ungulates.

A mixed model of the evolution of polygyny and sexual size dimorphism in mammals

AbstractThe theory of sexual selection is the most widely accepted theory explaining the evolution of mating systems and secondary sexual characters. Polygyny is the most common mating system in mammals, and there is a strong correlation between the degree of polygyny and the degree of sexual size dimorphism skewed towards males. Sexual selection theory posits that polygyny in mammals has evolved through direct, precopulatory, intrasexual selection in males, and that sexual size dimorphism is a result of male competition for mates. New results that are being obtained with the use of molecular techniques and with comparative phylogenetic methods do not appear to support predictions from this classical model in full. In this article, an expansion of the classical model is presented that combines the effects of at least four forms of selection: natural, precopulatory intrasexual, postcopulatory intrasexual, and intersexual selection. This mixed model consists of an initial phase in which natural selection operates on body size, followed by a second phase dominated by sexual selection and involving increases in sexual dimorphism and coercive behaviour of males towards females. Sexual harassment induces female aggregation, thus creating social potential for polygyny. Males compete for access to the groups of females, following two possible evolutionary scenarios, directional or equilibrium sexual selection, both producing similar behavioural polygyny, but with differences in the intensity of intra‐male precopulatory sexual selection. Predictions of the mixed model are as follows: 1) polygyny can exist without high variance in male reproductive success (a fundamental requirement in the classical model); 2) extra‐group fertilisation can be common; 3) sexual size dimorphism evolved prior to polygyny; 4) sexual coercion is widespread; and 5) females reduce levels of sexual coercion by joining groups.

Climatic conditions cause spatially dynamic polygyny thresholds in a large mammal.

The polygyny threshold (PT) is a critical transition point in the sexual selection process for many organisms in natural populations, characterizing when females choose to mate with an already mated male over an unmated one to improve fitness. Understanding its causes and consequences is therefore of high interest. While both theoretical and empirical work suggest that the degree of polygyny within a species is plastic and a function of male inequality, the functional relationship between underlying availability of resources occupied by breeding males under variable climatic conditions and the dynamics of PTs across space and time has received less attention. Here, we use a standardized measure of male mating inequality as the culmination of female mate choices to analyse how spatially dynamic PTs in a naturally regulated feral horse (Equus ferus caballus) population emerge along a geographic gradient in a known, limiting resource (freshwater) each year from variable climatic conditions. Polygyny threshold distance from permanent freshwater increased with increasing precipitation during the breeding season of each year, suggesting a relationship between annual resource availability and female mate choice. The mechanism by which climatic conditions underpin the spatial dynamics of PTs was likely through precipitation providing ephemeral freshwater sources across the study area that effectively weakened the gradient in availability of permanent freshwater, thereby providing mating males that occupied home ranges far from permanent water with access to this limiting resource and enabling them to attract and retain females. Increased precipitation also coincided with a decreased proportion of males in the population that experienced sexual selection pressure attributed to female mate choice in relation to the acquisition and/or defence of freshwater sources. Climatic conditions caused spatial shifts in PTs annually along the geographic gradient in resource availability. Our findings reveal that such environmental gradients may either buffer or amplify impacts of climatic variation on selection pressure operating in natural populations, and emphasize the importance of integrating spatially explicit PTs with atmospheric fluctuations when predicting the effect of climatic change on selection processes within populations that occupy environmental gradients.

Is offspring dispersal related to male mating status? An experiment with the facultatively polygynous spotless starling

Patterns of natal dispersal are generally sex‐biased in vertebrates, i.e. female‐biased in birds and male‐biased in mammals. Interphyletic comparisons in mammals suggest that male‐biased dispersal occurs in polygynous and promiscuous species where local mate competition among males exceeds local resource competition among females. However, few studies have analysed sex‐biased patterns of dispersal at the individual level, and facultatively polygynous species might offer this opportunity. In the spotless starling, polygynous males exhibit their mating status during courtship carrying higher amounts of green plants to nests than monogamous males. We experimentally incorporated green plants to nests during four years to analyse long‐term consequences on breeding success and offspring recruitment rates. We unexpectedly found that experimental sons recruited farther than experimental daughters, while control daughters recruited farther than control sons. A similar pattern was found using observational information from eight years. We discuss this result in the context of local competition hypothesis and speculate that sons dispersed farther from nests controlled by polygynous males to avoid competition with relatives. The amount of green plants in nests affects female perception of male attractiveness and degree of polygyny, although little is known about proximate mechanisms linking this process with the offspring dispersal behaviour. Our results support the idea that male‐biased dispersal is related to polygyny in a facultatively polygynous bird.

A comparative approach to testing hypotheses for the evolution of sex-biased dispersal in bean beetles.

Understanding the selective forces that shape dispersal strategies is a fundamental goal of evolutionary ecology and is increasingly important in changing, human-altered environments. Sex-biased dispersal (SBD) is common in dioecious taxa, and understanding variation in the direction and magnitude of SBD across taxa has been a persistent challenge. We took a comparative, laboratory-based approach using 16 groups (species or strains) of bean beetles (genera Acanthoscelides, Callosobruchus, and Zabrotes, including 10 strains of one species) to test two predictions that emerge from dominant hypotheses for the evolution of SBD: (1) groups that suffer greater costs of inbreeding should exhibit greater SBD in favor of either sex (inbreeding avoidance hypothesis) and (2) groups with stronger local mate competition should exhibit greater male bias in dispersal (kin competition avoidance hypothesis). We used laboratory experiments to quantify SBD in crawling dispersal, the fitness effects of inbreeding, and the degree of polygyny (number of female mates per male), a proxy for local mate competition. While we found that both polygyny and male-biased dispersal were common across bean beetle groups, consistent with the kin competition avoidance hypothesis, quantitative relationships between trait values did not support the predictions. Across groups, there was no significant association between SBD and effects of inbreeding nor SBD and degree of polygyny, using either raw values or phylogenetically independent contrasts. We discuss possible limitations of our experimental approach for detecting the predicted relationships, as well as reasons why single-factor hypotheses may be too simplistic to explain the evolution of SBD.

The influence of growth patterns on sexual size monomorphism in lemurs.

The lack of sexual size dimorphism among lemurs is puzzling given the high degree of polygyny in this clade. It has been proposed that the unique ecological conditions of Madagascar favour rapid completion of growth, limiting the opportunities for bimaturism and sexual size dimorphism in lemurs. Using recently compiled large data sets on many species across the lemur clade, I examined the prevalence of sexual size monomorphism of body mass among lemurs and tested the hypothesis that limited growth durations constrain sexual size dimorphism. I used segmented regression analyses to accurately model growth in each species. The majority of species analysed exhibited a period of rapid growth followed by a distinct period of slow growth prior to attainment of adult body mass. Whereas the first period of growth was constrained by the need to attain the majority of adult body mass prior to the onset of the infant's first dry season, the subsequent period of slow growth was unconstrained and sufficiently long to promote sexual bimaturism. Sex differences in the duration and rate of growth during this second growth phase appeared to account for the sexual size dimorphism exhibited by three lemur species. Therefore, constraints on growth processes do not limit sexual size dimorphism in lemurs, and other explanations for the prevalence of sexual size monomorphism in this clade should be examined. The importance of considering ontogeny in future investigations of sexual size monomorphism in lemurs is highlighted.

Why have parasites promoting mating success been observed so rarely?

Host manipulation by sexually transmitted parasites which increases host mating rate and thus parasite transmission rate has long been viewed as a plausible parasite adaptation. However, empirical evidence for it is rare. Here, using an adaptive dynamics approach to evolution, we explore conditions under which such disease-induced mating enhancement is (or is not) likely to occur. We find that increased mating success is less likely to evolve if the host reproduction rate, or the baseline disease transmission rate, is reduced, and the parasite affects just one sex, compared to when it affects both. We also find that it is less likely to evolve if the virulence-transmission trade-off curve is stronger, since we assume that enhanced disease transmission can only be achieved at the cost of increased virulence and as this trade-off is concave. In addition, we demonstrate that if disease-induced mating enhancement is equally acting in both sexes the mating system has no effect on evolutionary outcomes. On the contrary, if disease-induced mating enhancement is acting in just one sex, the potential for its evolution increases with the degree of polygyny in the host population. To study the examined phenomenon in greater detail we encourage further empirical research on this apparently less explored impact of sexually transmitted parasites on host fitness.

Cooperation and competition in a cliff-dwelling people

In animals that breed cooperatively, adult individuals will sometimes delay reproduction to act as helpers at the nest who raise young that are not their genetic offspring. It has been proposed that humans are also a cooperatively breeding species because older daughters, grandmothers, and other kin and nonkin may provide significant childcare. Through a prospective cohort study of children's (n = 1,700) growth and survival in the Dogon of Mali, I show that cooperative breeding theory is a poor fit to the family dynamics of this population. Rather than helping each other, siblings competed for resources, producing a tradeoff between the number of maternal siblings and growth and survival. It did not take a village to raise a child; children fared the same in nuclear as in extended families. Of critical importance was the degree of polygyny, which created conflicts associated with asymmetries in genetic relatedness. The risk of death was higher and the rate of growth was slower in polygynous than monogamous families. The hazard of death for Dogon children was twofold higher if the resident paternal grandmother was alive rather than dead. This finding may reflect the frailty of elderly grandmothers who become net consumers rather than net producers in this resource-poor society. Mothers were of overwhelming importance for child survival and could not be substituted by any category of kin or nonkin. The idea of cooperative breeding taken from animal studies is a poor fit to the complexity and diversity of kin interactions in humans.

Rethinking birdsong evolution: meta-analysis of the relationship between song complexity and reproductive success

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. Key words: extrapair paternity, female choice, repertoire size, sexual selection, trait expression. [Behav Ecol]

Polygyny in thief ants responds to competition and nest limitation but not food resources

Colonies of ants often house multiple queens, and variation in polygyny often tracks environmental conditions. Three hypotheses have been proposed to describe how environmental variation may account for the degree of polygyny: competition, food limitation and nest limitation. Here I evaluate these hypotheses with studies on litter-nesting thief ants (Solenopsis spp.) throughout a lowland tropical rain forest in Costa Rica. In one component, I measured how polygyny varied across a broad environmental gradient demonstrating substantial variation in resources and competition. In a second component, I manipulated the abundance of food, the spatial presentation of food and the availability of nesting space to assess the effects on queen number. The degree of polygyny increased with nest limitation and competition, but there was no indication that colonies produce queens to capitalize on food availability. The increase in queen number in response to the density of competitors suggests that an increase in queen number enhances exploitative abilities.

Population genetics of Formica ants

Enzyme gene variability was studied in European populations of 13 Formica ant species. Average gene diversity within nests ranged in different species from 0 to 0.047 and within populations from 0 to 0.078, the averages being 0.015 and 0.043, respectively. The results are consistent with earlier studies and theoretical models, which predict reduced genic variation in haplodiploid species. The evolutionary strategies of aculeate Hymenoptera may deviate the genetic structure of populations to the same direction as haplodiploidy, either by stabilizing environmental conditions or splitting the population into small groups with increasing ability to inbreeding. The results indicate genotype-environment interaction, as the average gene diversity was lower in nests and populations of mound-building species with stable and permanent nests, than in ground-nesting species. This was partly due to the social structure of the populations, as such a difference was not observed among the monogynous species. The amount of variation increased with increasing degree of polygyny and polycaly among the ground-nesting species, but not in the mound-building species. Geographic differences between conspecific populations were small. Differentiation was remarkable only between disjunct populations of F. aquilonia from Finland and Scotland.

The Relationship between Roosting Ecology and Degree of Polygyny in Harem-Forming Bats: Perspectives fromCynopterus

Within the broad continuum of polygyny, the mating systems of harem-forming bats exhibit a high degree of interspecific diversity and intraspecific variation. Here, I review the social structure and mating systems of 4 nominal species in the Old World fruit bat genus Cynopterus, and explore the relationship between roosting ecology, the size and stability of female groups, and variation in degree of polygyny. Intraspecific comparisons for C. brachyotis Sunda and C. sphinx suggest that the distribution and availability of suitable roost sites has a strong influence on the dispersion of females among males. Examination of paternity data for C. sphinx demonstrates a direct relationship between the environmental potential for polygyny and variance in male reproductive success: a 2-fold increase in mean harem size due to reduction in roost availability produces a 2-fold increase in reproductive skew among males. However, in C. brachyotis Sunda, C. sphinx, and C. horsfieldii, low fidelity of females to roosts or males is consistent, regardless of roost dispersion or permanence. In contrast, female C. brachyotis Forest exhibit high short-term fidelity to males, despite low roost fidelity. It is proposed that female lability is influenced by the distribution of potential mates and the benefits of multiple mating and, in C. brachyotis Sunda and C. sphinx, is likely to promote both behavioral and cryptic female choice, and male sperm competition.

Body Mass, Territory Size, and Life-History Tactics in a Socially Monogamous Canid, the Red FoxVulpes vulpes

Male-biased sexual size dimorphism is typical of polygynous mammals, where the degree of dimorphism in body mass is related to male intrasexual competition and the degree of polygyny. However, the importance of body mass in monogamous mammals is largely unknown. We investigated the effect of body mass on life-history parameters and territory size in the red fox (Vulpes vulpes), a socially monogamous canid with slight sexual dimorphism. Increased body size in males appeared to confer an advantage in territory acquisition and defense contests because heavier males held larger territories and exerted a greater boundary pressure on smaller neighbors. Heavier male foxes invested more effort in searching for extrapair matings by moving over a wider area and farther from their territories, leading to greater reproductive success. Males that sired cubs outside their own social group appeared to be heavier than males that only sired cubs within their social group or that were cuckolded, but our results should be treated with caution because sample sizes were small. Territory size, boundary pressure, and paternity success were not related to age of males. In comparison, body mass of females was not related to territory size, probability of breeding, litter size, or cub mass. Only age affected probability of breeding in females: younger females reproduced significantly less than did older females, although we did not measure individual nutritional status. Thus, body mass had a significant effect on life-history traits and territory size in a socially monogamous species comparable to that reported in polygynous males, even in the absence of large size dimorphism.

Patterns of male reproductive success in a highly promiscuous whale species: the endangered North Atlantic right whale

Parentage analyses of baleen whales are rare, and although mating systems have been hypothesized for some species, little data on realized male reproductive success are available and the patterns of male reproductive success have remained elusive for most species. Here we combine over 20 years of photo-identification data with high-resolution genetic data for the majority of individual North Atlantic right whales to assess paternity in this endangered species. There was significant skew in male reproductive success compared to what would be expected if mating was random (P < 0.001). The difference was due to an excess of males assigned zero paternities, a deficiency of males assigned one paternity, and an excess of males assigned as fathers for multiple calves. The variance in male reproductive success was high relative to other aquatically mating marine mammals, but was low relative to mammals where the mating system is based on resource- and/or mate-defence polygyny. These results are consistent with previous data suggesting that the right whale mating system represents one of the most intense examples of sperm competition in mammals, but that sperm competition on its own does not allow for the same degree of polygyny as systems where males can control access to resources and/or mates. The age distribution of assigned fathers was significantly biased towards older males (P < 0.05), with males not obtaining their first paternity until approximately 15 years of age, which is almost twice the average age of first fertilization in females (8 years), suggesting that mate competition is preventing younger males from reproducing. The uneven distribution of paternities results in a lower effective population size in this species that already has one of the lowest reported levels of genetic diversity, which may further inhibit reproductive success through mate incompatibility of genetically similar individuals.

Genetic similarity, breeding distribution range and sexual selection

Large populations with extensive breeding distributions may sustain greater genetic variability, thus producing a positive relationship between genetic variation and population size. Levels of genetic variability may also be affected by sexual selection, which could either reduce levels because a small fraction of males contribute to the following generation, or augment them by generating genetic variability through elevated rates of mutations. We investigated to what extent genetic variability, as estimated from band sharing coefficients for minisatellite markers, could be predicted by breeding distribution range, population size and intensity of sexual selection (as reflected by degree of polygyny and extra-pair paternity). Across a sample of 62 species of birds in the Western Palearctic, we found extensive interspecific variation in band sharing coefficients. High band sharing coefficients (implying low local genetic variability among individuals) were associated with restricted breeding distributions, a conclusion confirmed by analysis of statistically independent linear contrasts. Independently, species with large population sizes had small band sharing coefficients. Furthermore, bird species with a high richness of subspecies for their breeding distribution range had higher band sharing coefficients. Finally, bird species with high levels of polygyny and extra-pair paternity had small band sharing coefficients. These results suggest that breeding distribution range, population size and intensity of sexual selection are important predictors of levels of genetic variability in extant populations.

Effect of temperature on the oviposition rate of Argentine ant queens ( Linepithema humile Mayr) under monogynous and polygynous experimental conditions

Data concerning the influence of temperature on a species’ physiological parameters can be a useful tool for predicting its potential distribution range, but in the case of the Argentine ant, data based on its physiological needs are too scarce and incomplete to make accurate predictions of this type. In the present study, we offer new and complete data concerning the Argentine ant queen's oviposition rate under a wide range of temperatures in the laboratory. We analyzed the oviposition rate of the Argentine ant ( Linepithema humile) at 12 experimental temperatures: 10, 12, 14, 16, 18, 21, 24, 26, 28, 30, 32 and 34 °C under monogynous conditions (one queen per nest) and three different polygynous conditions (two, four and eight queens per nest). We found that temperature affected their oviposition rate and that the effect was similar regardless of the number of queens in the nest. Egg laying was at its maximum at 28 °C, with variation in the upper and lower temperature limits at which oviposition took place depending on the degree of polygyny. Oviposition rates were negatively correlated with the number of queens in the nest. We also observed a marked variation in the oviposition rate of queens subjected to the same experimental conditions.

INDIVIDUAL VOCAL IDENTITY IN MOTHER AND PUP AUSTRALIAN SEA LIONS (NEOPHOCA CINEREA)

Individual vocal recognition between mothers and pups has been widely observed in pinnipeds, especially otariids. Otariids are colonial breeders; mothers suckle only their own offspring, aggressively attacking nonrelated young. Mothers alternate foraging trips with periods ashore, and at each return to the colony, mothers and pups must find each other among all the individuals of the colony. In the Australian sea lion (Neophoca cinerea), the need for a finely tuned mechanism of recognition is exacerbated by their habit of changing the nursing location over the course of lactation. We investigated potential acoustic parameters used in mother‐pup recognition in Australian sea lions. We measured 11 acoustic parameters on calls of mothers and pups and found that several parameters (fundamental frequency, energy spectrum, amplitude, and frequency modulation) were highly individually specific. Discriminant analysis correctly assigned calls to individual mothers or pups with an average classification rate of 65% and 77%, respectively. Spectral features and frequency modulation were the most important features distinguishing individuals. Lastly, principal component analysis showed that calls of pups and mothers were easily distinguishable using energy spectrum and frequency modulation. Comparison with other pinniped species suggests that individual vocal identity is likely to be selected through ecological constraints such as density of the colony, degree of polygyny, likelihood of allosuckling or fostering, and degree of maternal absence during lactation.

Paternity loss in contrasting mammalian societies

Recent genetic analyses show that, in social mammals, loss of paternity by breeding males varies with strategies of mate guarding rather than with the degree of polygyny.