Polygynous Males Research Articles

Do polygynous males of Akodon azarae (Rodentia: Sigmodontinae) vary their mating tactics at low availability of females?

AbstractWe examined in

Seeking a Sex‐Specific Coolidge Effect in a Simultaneous Hermaphrodite

AbstractIn polygamous mating systems, a capability to discriminate against familiar mates may be beneficial to both sexes. Polyandrous females, for instance, may enhance the odds of finding sires with optimal genetic compatibility or high genetic quality by mating with multiple different males; polygynous males, in addition, may more efficiently invest their limited ejaculates across multiple (rather than single) females. The Coolidge effect facilitates this kind of mate discrimination, as sexual motivation declines across consecutive copulations with a familiar partner but resurrects with a novel mate. In simultaneous hermaphrodites, we expect the Coolidge effect to show sex role‐dependent patterns and vary with previous sex‐specific mating activity. Using the promiscuous hermaphroditic sea slug Chelidonura sandrana, we investigated (1) whether sexual motivation indeed declines when repeatedly exposed to familiar partners, (2) whether the Coolidge effect occurs in a sex‐specific manner and (3) whether ejaculation is strategic with respect to partner familiarity. We found neither mating latency, nor penis intromission duration, mating propensity or the frequency of sex role alternations to vary significantly with treatments. Furthermore, slugs did not donate larger ejaculates to novel than to familiar partners. Partner novelty thus elicited no detectable response in sexual motivation or mating effort in C. sandrana. We suggest that the sea slugs' promiscuous mating system in often large mating aggregations makes mate discrimination based on novelty obsolete in comparison with more relevant criteria such as partner body size or mating history.

Simulating Retention of Rare Alleles in Small Populations to Assess Management Options for Species with Different Life Histories

Preserving allelic diversity is important because it provides the capacity for adaptation and thus enables long-term population viability. Allele retention is difficult to predict in animals with overlapping generations, so we used a new computer model to simulate retention of rare alleles in small populations of 3 species with contrasting life-history traits: North Island Brown Kiwi (Apteryx mantelli; monogamous, long-lived), North Island Robins (Petroica longipes; monogamous, short-lived), and red deer (Cervus elaphus; polygynous, moderate lifespan). We simulated closed populations under various demographic scenarios and assessed the amounts of artificial immigration needed to achieve a goal of retaining 90% of selectively neutral rare alleles (frequency in the source population = 0.05) after 10 generations. The number of immigrants per generation required to meet the genetic goal ranged from 11 to 30, and there were key similarities and differences among species. None of the species met the genetic goal without immigration, and red deer lost the most allelic diversity due to reproductive skew among polygynous males. However, red deer required only a moderate rate of immigration relative to the other species to meet the genetic goal because nonterritorial breeders had a high turnover. Conversely, North Island Brown Kiwi needed the most immigration because the long lifespan of locally produced territorial breeders prevented a large proportion of immigrants from recruiting. In all species, the amount of immigration needed generally decreased with an increase in carrying capacity, survival, or reproductive output and increased as individual variation in reproductive success increased, indicating the importance of accurately quantifying these parameters to predict the effects of management. Overall, retaining rare alleles in a small, isolated population requires substantial investment of management effort. Use of simulations to explore strategies optimized for the populations in question will help maximize the value of this effort..

Is shared male assistance with antiparasitic nest defence costly in the polygynous great reed warbler?

Polygyny typically has negative fitness consequences for secondary females, but may equally impose costs on primary females or even on polygynous males. We investigated how polygynous and monogamous great reed warbler, Acrocephalus arundinaceus , males assist their mates with aggressive nest defence against the common cuckoo, Cuculus canorus , and whether the females adjust their nest defence intensity according to male investment in aggression. Additionally, we investigated whether host social mating status affects host vulnerability to parasitism. We presented taxidermic cuckoo mounts at nests of primary, secondary and monogamous females, and recorded aggressive responses of nest owners. We found that monogamous males defended their nests most aggressively while polygynous males allocated their nest protection effort unevenly between their two mates, responding more vigorously on the primary than secondary nests. In contrast, nest defence intensity of females did not differ with respect to their social status, indicating that females of polygynous males did not compensate for low levels of male aggression. Similarly, we found no differences in natural cuckoo parasitism rates between monogamous, primary and secondary nests. Our results thus suggest that while monogamous females receive more assistance with nest defence than females of polygynous males, this has no effect on the probability of parasitism.

Positive association between social and extra-pair mating in a polygynous songbird, the dickcissel (Spiza americana)

In polygynous species, males appear to gain additional offspring by pairing with multiple females simultaneously. However, this may not be true if some females copulate outside of the social pair bond. Polygynous males could experience lower paternity because of trade-offs among gaining multiple social mates, guarding fertility with these mates, and pursuing extra-pair matings. Alternatively, polygynous males could simultaneously gain extra social mates and have high paternity, either because of female preferences or because of male competitive attributes. We tested four predictions stemming from these hypotheses in a facultatively polygynous songbird, the dickcissel (Spiza americana). Unlike most previous studies, we found that males with higher social mating success (harem size) also tended to have higher within-pair paternity and that the number of extra-pair young a male sired increased significantly with his social mating success. Females that paired with mated males were not more likely to produce extra-pair young. In contrast, extra-pair paternity was significantly lower in the nests of females whose nesting activity overlapped that of another female on the same territory. This pattern of mating was robust to differences in breeding density. Indeed, breeding density had no effect on either extra-pair mating or on the association between polygyny and paternity. Finally, nest survival increased with harem size. This result, combined with the positive association between polygyny and paternity, contributed to significantly higher realized reproductive success by polygynous male dickcissels.

Breeding success of a brood parasite is associated with social mating status of its host

Reproductive success of brood parasites varies considerably both among and within host species, mainly due to differences in host egg-rejection rates and survival of parasitic chicks. Here, we investigated the breeding success of the cuckoo (Cuculus canorus) in one of its major hosts, the great reed warbler (Acrocephalus arundinaceus), with respect to host social mating status. In this passerine, polygynous males provide less parental care to their young per nest than monogamous males. Consequently, their less-assisted females may fledge lower numbers of nestlings than monogamous females. This may be especially true for secondary females, which often receive limited or no paternal help with young at all. Based on these findings, we expected higher cuckoo reproductive success in nests of socially monogamous than polygynous great reed warbler males. More specifically, we predicted lower fledging success of cuckoo young in nests of secondary than primary or monogamous females. In line with the prediction, we found higher cuckoo fledging success in nests of monogamous than polygynous males, monogamous nests being more than twice as successful as secondary nests. We detected, however, only a tendency to lower cuckoo success in primary compared to monogamous nests and no differences between primary and secondary nests. Moreover, neither parasitism nor host egg-rejection rates differed among the nests of different status. Our results show, for the first time, that the social mating status of a host may influence the overall reproductive success of a brood parasite and thus should be considered in further studies.

Mating systems in cooperative breeders: the roles of resource dispersion and conflict mitigation

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. Key words: cooperative breeding, mating system, monogamy, polygyny, resource dispersion, sexual conflict. [Behav Ecol]

How do Southern House Wrens Troglodytes aedon musculus achieve polygyny? An experimental approach

I designed two experiments to evaluate how polygyny is achieved in Southern House Wrens (Troglodytes aedon musculus) breeding in a south-temperate population. In the first experiment, I manipulated territory attractiveness by adding high quality nesting sites (nest-boxes) to 50% of monogamous territories (n = 24) and evaluated if males can attract a second female when defending high quality resources. In the second experiment, I simulated high male mortality early in the breeding season by removing 30 territorial males in plots where wrens had been breeding in nest-boxes (n = 47 territories). The first experiment did not induce polygyny: although females switched from breeding in tree cavities to nest-boxes when boxes were erected on their territory, none of the neighbouring females who did not receive a box moved to breed as a secondary female. The male removal experiment did induce polygyny: of 21 experimentally widowed females, 38% bred as secondary females of neighboring males—who expanded their territories in the absence of a defending male—and accepted polygyny even in the presence of neighbouring territories held by bachelor males. Secondary females mated to polygynous males were rarely helped by the male while feeding nestlings, but primary and secondary females overlapped very little in the use of space. Hence, females mated to polygynous males may share parental care disproportionally but not territorial resources. Female attachment to territories and exclusive use of space together with male’s expansion of territories to achieve polygyny suggests that Southern House Wrens engage in sublease polygyny.

Polygynous great reed warblers Acrocephalus arundinaceus suffer more cuckoo Cuculus canorus parasitism than monogamous pairs

There is increasing evidence that hosts within a population may not be parasitized by common cuckoos Cuculus canorus with equal probability. Such non-randomness has been documented, for example, for host nest sites and host quality. In this study we demonstrate association between successful cuckoo parasitism and host social mating system. We found that nests of socially polygynous great reed warblers Acrocephalus arundinaceus were more often successfully parasitized than the nests of their monogamous counterparts. We hypothesize that lack of parental assistance provided by polygynous males to their mates during egg laying period and higher nest activity in their territories could contribute to this discrepancy. These data imply that social mating system should be taken into account in future studies of brood parasitism.

Fit females and fat polygynous males: seasonal body mass changes in the grey-headed flying fox

When females and males differ in their timing of maximum reproductive effort, this can result in sex-specific seasonal cycles in body mass. Such cycles are undoubtedly under strong selection, particularly in bats, where they affect flying ability. Flying foxes (Old World fruit bats, Pteropus spp.) are the largest mammals that can sustain powered flight and therefore face critical trade-offs in managing body reserves for reproduction, yet little is known about body mass dynamics in this group. I investigated body mass changes in relation to reproductive behaviour in a large colony of grey-headed flying foxes (Pteropus poliocephalus). In this polygynous mammal, females were predicted to maximise reproductive effort during lactation and males during the breeding season. As predicted, female body condition declined during the nursing period, but did not vary in relation to sexual activity. By contrast, males accumulated body reserves prior to the breeding season, but subsequently lost over 20% of their body mass on territory defence and courtship, and lost foraging opportunities as they also defended their day roost territories at night. Males in better condition had larger testes, particularly during territory establishment, prior to maximum sexual activity. Thus, the seasonality of female mass reflected the high metabolic load that lactation imposes on mothers. However, male mass followed a pattern akin to the "fatted male phenomenon", which is commonly observed in large polygynous mammals with seasonal reproduction, but not in bats. This shows the importance of body reserves for reproduction in flying foxes, despite their severe constraints on body mass.

Environment and activity affect skin temperature in breeding adult male elephant seals (Mirounga angustirostris)

The large body size and high rates of metabolic heat production associated with male mating success in polygynous systems creates potential thermoregulatory challenges for species breeding in warm climates. This is especially true for marine predators carrying large blubber reserves intended for thermoregulation in cold water and fuel provision during extended fasts. Thermographic images were used to measure changes in skin temperature (T(S)) in adult male northern elephant seals (Mirounga angustirostris) over the breeding season. Environmental variables, primarily ambient temperature and solar radiation, were the principal determinants of mean and maximum T(S). When controlled for environmental variables, dominance rank significantly impacted mean T(S), being highest in alpha males. Behavioral activity significantly influenced T(S) but in a counter-intuitive way, with inactive males exhibiting the highest T(S). This was likely due to strong impacts of environmental variables on the kinds of behavior exhibited, with males being less active on warm, humid days at peak solar radiation. We classified thermal windows as areas in which T(S) was one standard deviation greater than mean T(S) for the individual seal within a thermograph. Thermal features suggest active physiological thermoregulation during and after combat and significant circulatory adaptations for heat dumping, as evidenced by recurring locations of thermal windows representing widely varying T(S) values. Frequent observations of localized T(S) above 37°C, particularly after combat, suggest the production of thermoregulatory stress during breeding behavior. Our findings demonstrate the importance of environmental drivers in shaping activity patterns during breeding and provide evidence for thermoregulatory costs of successful breeding in large polygynous males.

Polygyny and extra-pair paternity enhance the opportunity for sexual selection in blue tits

Polygyny and extra-pair paternity are generally thought to enhance sexual selection. However, the extent to which these phenomena increase variance in male reproductive success will depend on the covariance between success at these two strategies. We analysed these patterns over four breeding seasons in facultatively polygynous blue tits Cyanistes caeruleus. We found that both polygyny and extra-pair paternity increased variance in male reproductive success and that standardised variance in annual number of genetic fledglings was 2.6 times higher than standardised variance in apparent success when assuming strict monogamy. Nevertheless, male success at securing within-pair paternity was unrelated to success at gaining extra-pair paternity and, when considering the positive effect of age on extra-pair success and attracting a second female, polygynous males were no more likely to sire extra-pair fledglings. Overall, polygynous males fledged more genetic offspring than monogamous males, but first-year polygynous males lost a greater share of within-pair paternity. A literature review suggests that this adverse effect of polygyny on within-pair paternity is frequent among birds, inconsistent with the prediction that females engage in extra-pair copulation with successful males to obtain good genes. Furthermore, a male's share of paternity was repeatable between years, and among females of polygynous males within years, such that a compatibility function of extra-pair copulations was likewise unsupported. Instead, we suggest that the observed patterns are most consistent with a fertility insurance role for extra-pair copulations, which does not exclude the greater opportunity for sexual selection through differential ability of males to gain paternity.

Does Social Mating System Influence Nest Defence Behaviour in Great Reed Warbler (Acrocephalus arundinaceus) Males?

AbstractIn birds with biparental care, males and females often conflict over how much care to provide to their offspring and it may be substantially influenced by increased level of polygamy. In accordance with sexual conflict theory, males of socially polygynous bird species provide much less care to their nestlings than do males of most socially monogamous species. Most of previous studies, however, have used feeding behaviour as an index for variations in male parental care only. However, this may be skewed if polygynous males compensate for lower feeding assistance through the provision of other parental care such as protection of nests from predators. In this paper, we examine nest defence behaviour in the facultatively polygynous great reed warbler with respect to sex and type of social mating system. We recorded latency to the first arrival, distance from the predator and defensive reaction of each parent towards a human intruder. Socially polygynous males with two simultaneously active nests defended primary females’ nests less vigorously than socially monogamous males, whereas no differences were found between monogamous and primary females. Generally, however, they took a bigger role in nest defence than males in all cases. Our results support an idea that sexual conflict is driven by polygamy and that type of social mating system can influence nest defence behaviour of facultatively polygynous birds. This finding should be taken into consideration when studying nest defence parental care in polygynous mating systems.

Differential deposition of antimicrobial proteins in blue tit (Cyanistes caeruleus) clutches by laying order and male attractiveness

Female birds can influence offspring fitness by varying the relative quantities of egg components they deposit within and between clutches. Antimicrobial proteins (lysozyme, ovotransferrin, and avidin) are significant components of the avian albumen and likely aid in defense of embryos from microbial infection. Within clutches, females may enhance antimicrobial defense of early-laid eggs to protect them from the high risk of infection incurred before the onset of incubation. Among entire clutches, females may invest more resources in young sired by more attractive males because they have higher reproductive value. We tested these hypotheses by quantifying antimicrobial protein distribution within and among clutches in blue tit eggs. Contrary to our hypothesis, clutches showed no differential deposition of lysozyme or avidin within clutches, but eggs laid in the middle of the sequence had higher concentrations of ovotransferrin than eggs in the beginning and end. Consistent with our second hypothesis, we found that females produced eggs with higher concentrations of lysozyme (although not ovotransferrin or avidin) when mated to more attractive (more UV-reflective) males. Furthermore, females mated to polygynous males deposited less lysozyme than those mated to monogamous males. These data suggest that allocation of lysozyme at the clutch level may be a maternal effect mediated by male qualities.

Isometric scaling in home-range size of male and female bobcats (Lynx rufus)

For solitary carnivores a polygynous mating system should lead to predictable patterns in space-use dynamics. Females should be most influenced by resource distribution and abundance, whereas polygynous males should be strongly influenced by female spatial dynamics. We gathered mean annual home-range-size estimates for male and female bobcats ( Lynx rufus (Schreber, 1777)) from previous studies to address variation in home-range size for this solitary, polygynous carnivore that ranges over much of North America. Mean annual home ranges for bobcats (171 males, 214 females) from 29 populations covering the entire north to south and east to west range demonstrated female home-range sizes varied more than an order of magnitude and that, on average, males maintained home ranges 1.65 times the size of females. Male home-range sizes scaled isometrically with female home-range sizes indicating that male bobcats increase their home-range size proportional to female home-range size. Using partial correlation analysis we also detected an inverse relationship between environmental productivity, estimated using the normalized difference vegetation index, and home-range size for females but not males. This study provides one of the few empirical assessments of how polygyny influences home-range dynamics for a wide-ranging carnivore.

Female androgen patterns and within-pair testosterone compatibility in domestic geese ( Anser domesticus)

For successfully raising offspring, long-term monogamous pair partners need to be behaviorally and hormonally coordinated. In the monogamous, biparental greylag geese ( Anser anser) a dyadic pairbond-specific measure, ‘within-pair testosterone compatibility’ (TC) indicated how closely synchronized are seasonal androgen levels, which co-varied with reproductive output. Males, in particular, were assumed to respond to their females’ hormonal and fecundity phases. We now present experiments with biparental domestic geese ( Anser domesticus) kept as pairs to ask whether TC occurs also in these generally polygynous animals. We further ask how different conditions of mate choice affect TC and whether established TC is maintained during a polygynous flock situation. We measured androgen metabolites (AM) non-invasively from individual droppings. In females, AM was related with gonadal activity as it increased after GnRH but not ACTH challenge. Females with preferred partners had higher maximum AM during egg laying and higher rates of initiating incubation than randomly paired females. Domestic ganders had seasonal AM patterns typical for polygynous males. Within-pair TC ranged from almost perfectly positive to non-correlated in domestic geese but mate choice did not explain TC variation. TC of previous pairs was generally reduced in the flock situation, probably confounded by factors of the social environment, i.e. mating opportunity and availability of multiple partners. On top of the underlying reproductive physiology our results suggest two episodic components of TC: a female androgen responsiveness to the preferred partner at least during egg formation, and the male’s facultative potential to respond to her readiness to breed.

Polygyny in the tree swallow Tachycineta bicolor: a result of the cost of searching for an unmated male

The costs imposed by parental care duties on an individual's future survival and reproduction generate conflicts because parents should attempt to minimize their investment in the present brood, and exploit the parental care of the other parent. This conflict is likely to contribute to cases of both polygamy and desertion. Here, we study the costs of polygyny in the tree swallow Tachycineta bicolor, using observations on 52 nests that were attended by polygynous males over 14 y. Both females mated to polygynous males paid reproductive costs at several stages of the nesting cycle. Clutches laid by social mates of polygynous versus monogamous males did not differ in size. However, initial brood sizes for polygynously mated females were lower because a higher proportion of their eggs failed to hatch. Likewise, fledging success was lower and nest predation rates were higher, perhaps reflecting the direct or indirect effects of reduced male attention. These results demonstrate that females pay a productivity cost when breeding with reduced male parental care. In contrast, polygynous males fledge on average more young than monogamous ones and clearly benefit from the association. We suggest that a mate‐search cost is leading to the few cases of polygamous males: although females are likely evaluating males for their prospective dedication to the breeding attempt, in a short‐lived bird with a short breeding season, the cost to females of searching for a more dedicated male is the risk of not breeding at all.

Repertoire Sizes of the Whistle and Trill Parts of the Song of the Grey Thrush Turdus cardis in Relation to the Mating Success of the Males

The relationship between the song repertoire and breeding success of birds has been studied for several species. In some species, the different components of the songs have different functions and are suggested to have evolved under different intra- and intersexual selection pressures. The song of the Grey Thrush Turdus cardis consists of the whistle and trill parts. In this study, it was clarified that the repertoire sizes of the syllables in both parts did not correlate with each other, suggesting the possibility that both parts have evolved under different sexual selection pressures. The repertoire sizes also did not correlate with the age of the birds. The relationship between the repertoire size and the mating status of males was also examined. The whistle repertoire size was not related to the mating status, while the trill repertoire size in polygynous males was larger than that in monogamous males. This result suggests that the functions of the two parts of the song are not similar, a finding consistent with the results of previous studies indicating that the complexity of trills has evolved under intersexual selection pressure.

Male song repertoire size and syllable sharing of oriental great reed warblers, acrocephalus orientalis

The size of song repertoires mainly provides evidence for explaining sexual selection for female choice as well as male‐male competition. We investigated the role of oriental great reed warbler songs (Acrocephalus orientalis) of breeding territorial males. Early arrived males possessed larger song repertoires, paired earlier, and tended to become polygynous. No correlation was found between arrival date and territory size, but polygynous males significantly occupied larger territories than non polygynous males. Song sharing was low among males and the degree of similarity did not relate with spatial distance. Our results suggest that song repertoire of the oriental great reed warbler males play a role in female choice, where territory quality may affect male pairing success.

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.