Male Reproductive Strategies Research Articles

Hormonal Correlates of Divergent Growth Trajectories in Wild Male Anubis (Papio anubis) and Hamadryas (P. hamadryas) Baboons in the Awash River Valley, Ethiopia

Comparative investigations of hormone concentration and pattern during ontogeny can offer insight regarding the evolution of growth trajectories. Anubis (Papio anubis) and hamadryas (P. hamadryas) baboons exemplify primate populations at a crucial stage of phylogenetic divergence. Though not reproductively isolated, the species are distinguished by consistent morphological, behavioral, and physiological differences, including trajectories of growth and maturation associated with divergent male reproductive strategies. As a step toward understanding the proximate causes of these differences, we tested several hypotheses regarding the relationship of growth-regulatory hormones and binding proteins (insulin-like growth factor-I, insulin-like growth factor binding protein-3 [IGFBP-3], growth hormone binding protein, and testosterone) to growth in several measurements. We collected samples (N = 559) across 13 field seasons, from 7 different social groups. Samples came from 398 different individuals. We sampled 285 once; 76, twice; 29, three times; 5, four times; and 3, five times. Although ages at peak hormone concentrations were not significantly different, concentrations of all hormones and binding proteins measured, except testosterone, were higher in hamadryas than in anubis. All factors measured correlated positively with growth in both species, and IGFBP-3 and testosterone in particular correlated significantly with growth in all measurements. Overall, our findings suggest a role for the growth hormone/insulin-like growth factor axis in producing distinctive patterns of growth in these species.

Different ontogenetic patterns of testosterone production reflect divergent male reproductive strategies in chimpanzees and bonobos

Male reproductive effort is often strongly related to levels of the steroid hormone testosterone. However, little research has examined whether levels of testosterone throughout development might be tied to individual or species differences in the reproductive strategies pursued by adult males. Here, we tested the hypothesis that inter-specific differences in male reproductive strategy are associated with differences in the pattern of testosterone production throughout early life and puberty. We compared testosterone levels from infancy to adulthood in two closely related species where levels of mating competition and male–male aggression differ significantly, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). We predicted that the reduction in male mating competition found in bonobos would be accompanied by a lesser developmental increase in testosterone production. We performed radioimmunoassay of salivary testosterone levels in a mixed-longitudinal sample of both species, collected from individuals living in semi free-ranging populations. This allowed us to examine the effects of development in a more naturalistic setting than possible in a zoo or laboratory. We found that among chimpanzees, testosterone levels declined slightly from infancy to juvenility, then remained low until increasing markedly during adolescence (with pubertal increases most pronounced among males). In contrast, there was little change in testosterone production with age in bonobos of either sex, with levels of testosterone consistent throughout infancy, juvenility, and the transition to adulthood. Our data are therefore consistent with the hypothesis that the ontogenetic pattern of testosterone production can be subject to rapid evolutionary change, shifting in association with species differences in male reproductive strategy.

Male–female socio-spatial relationships and reproduction in wild chimpanzees

Recent research on primates and other taxa has shown that the relationships individuals form with members of the same sex affect their reproductive success. Evidence showing that intersexual relationships also influence reproduction, however, is more equivocal. Here, we show that male chimpanzees living in an exceptionally large community display long-term tendencies to associate with particular females. These association patterns are likely to arise because individuals of both sexes selectively range in specific areas of the communal territory, with males inheriting the ranging patterns of their mothers. These differentiated male–female socio-spatial relationships involved males of widely varying ranks, and their effect on reproduction is as strong as that of male dominance rank, which in turn is as strong a predictor of reproductive success at Ngogo as in other smaller chimpanzee communities. These results show that male–female socio-spatial relationships can play a large role in chimpanzee male reproductive strategies, although they probably neither weaken nor strengthen the relationship between male dominance rank and reproductive success. Our results linking male–female socio-spatial relationships to reproduction in chimpanzees suggest that the gap between the social and mating systems of humans and their closest living relatives may not be as large as previously thought.

Male reproductive strategy explains spatiotemporal segregation in brown bears

1. Spatiotemporal segregation is often explained by the risk for offspring predation or by differences in physiology, predation risk vulnerability or competitive abilities related to size dimorphism.2. Most large carnivores are size dimorphic and offspring predation is often intraspecific and related to nonparental infanticide (NPI). NPI can be a foraging strategy, a strategy to reduce competition, or a male reproductive strategy. Spatiotemporal segregation is widespread among large carnivores, but its nature remains poorly understood.3. We evaluated three hypotheses to explain spatiotemporal segregation in the brown bear, a size-dimorphic large carnivore in which NPI is common; the ‘NPI – foraging/competition hypothesis', i.e. NPI as a foraging strategy or a strategy to reduce competition, the ‘NPI – sexual selection hypothesis’, i.e. infanticide as a male reproductive strategy and the ‘body size hypothesis’, i.e. body-size-related differences in physiology, predation risk vulnerability or competitive ability causes spatiotemporal segregation. To test these hypotheses, we quantified spatiotemporal segregation among adult males, lone adult females and females with cubs-of-the-year, based on GPS-relocation data (2006–2010) and resource selection functions in a Scandinavian population.4. We found that spatiotemporal segregation was strongest between females with cubs-of-the-year and adult males during the mating season. During the mating season, females with cubs-of-the-year selected their resources, in contrast to adult males, in less rugged landscapes in relative close proximity to certain human-related variables, and in more open habitat types. After the mating season, females with cubs-of-the-year markedly shifted their resource selection towards a pattern more similar to that of their conspecifics. No strong spatiotemporal segregation was apparent between females with cubs-of-the-year and conspecifics during the mating and the postmating season.5. The ‘NPI – sexual selection hypothesis’ best explained spatiotemporal segregation in our study system. We suggest that females with cubs-of-the-year alter their resource selection to avoid infanticidal males. In species exhibiting NPI as a male reproductive strategy, female avoidance of infanticidal males is probably more common than observed or reported, and may come with a fitness cost if females trade safety for optimal resources.

The Limitations of Law as a Tool for Responding to Violence Against Women

In their article, Hudson, Bowen, and Nielsen (2011) argue that inequities in family law codify an evolutionary legacy of male control over female reproduction that correlates with increased rates of violence against women. Their general argument is comprised of three fundamental premises. First, the authors provide empirical evidence indicating a relationship between inequities in family law, defined as “state regulation of marriage, parenthood, dissolution of marriage, custody of children, and transmission of goods across generations” (454), and levels of physical violence against women in particular societies. Second, the authors anchor their general argument in a feminist evolutionary analytic approach (FEAA). They contend that evolutionary forces are an ultimate cause of patriarchy and violence against women, even as they acknowledge the importance of more proximate causes of specific forms of violence against women. According to the authors, an FEAA approach can help explain “persistent patterns of patriarchy throughout human history” (464) and “…tells us that there is a strong evolutionary component to violence, and that its origin is male-female conflict over reproduction, and that these influences will be mirrored in human systems of family law” (468). Finally, the authors draw upon the two previous premises to build the third and most critical premise of their argument. Because the authors believe that evidence showing a correlation between inequities in family law and levels of physical violence are ultimately rooted in evolutionary dynamics, they conclude that “[s]ocieties that persist in safeguarding inequitable family law are societies built upon evolutionary male reproductive strategies of structural control and higher levels of coercion of women by men” (470).

An insight into the reproductive biology of the bearded goby Sufflogobius bibarbatus

Preliminary results obtained from histological analyses of the male reproductive organs, supplemented with field and behavioural data, indicate that Sufflogobius bibarbatus, a small, slow growing gobiid exhibiting low fecundity, which plays an important role in the food web off Namibia, where large areas of the shelf are hypoxic, spawns demersally. Large males defend benthic nests, possibly at the edge of the hypoxic shelf. Male reproductive strategy appears to be flexible, and tentative evidence to suggest that polygyny and sneaking may also occur is presented.

The effect of the presence of quiescent female nymphs, males and their spermatophores on spermatophore placement in two species of eriophyoid mites

Under sex dissociated sperm transfer, females seek spermatophores and pick up sperm without male assistance. In several species males adjust spermatophore deposition rate to the presence of conspecifics. It is not known, however, which factors could favor such elasticity in non-pairing males. In this paper, we compare male response towards conspecifics between the sex dissociated eriophyoid mites Aculus fockeui (Nalepa and Trouessart) and Aculops allotrichus (Nalepa). The species differ significantly in male reproductive strategies and, consequently, the intensity of male–male-competition. Aculus fockeui males deposit spematophores all over the leaves and occasionally leave single spermatophores beside quiescent female nymphs (QFNs). In contrast, A. allotrichus males guard QFNs and encircle them with spermatophores. In this study, males of both species deposited spermatophores close to and apart from the rival spermatophores. Aculops allotrichus males had similar spermatophore output whether they were kept alone or in a group of seven males. They did not change spermatophore output in the presence of five rival spermatophores, a QFN or a QFN and varying number of rivals, either. In contrast, A. fockeui males increased spermatophore output in the presence of rival spermatophores or when on the arena with a QFN the male number increased to eight males. They did not respond, however, to the presence of a QFN and one rival or a QFN alone. The possible effect of the species-specific intensity of male–male competition, population density, the availability of receptive females and the rate of spermatophore output on the flexibility of eriophyoid spermatophore deposition is discussed.

Attacks on adult females with infants by non-resident males in the François langur

Infanticide by males is a common phenomenon in mammals, especially primates, as lactation lasts much longer than gestation in many species. Usually, infanticidal episodes occur soon after group takeovers, and are traditionally considered a male reproductive strategy (i.e., support the sexual selection hypothesis, Hrdy, 1974). To verify the validity of this conception, we observed one group of Francois' langurs in the Nonggang Nature Reserve, China, between August 2003 and July 2004. During the study period, a Francois' langur female with the youngest infant in the group was attacked three times by immigrating males, and later disappeared by the third day after the final attack. We suggest that these attacks on the female-infant dyad represent infanticide attempts by males, and may be the cause of the adult female and her infant's disappearance. Presumably, that female dispersed with her infant to avoid infanticide and was not killed. Though these observations do not completely verify the sexual selection hypothesis, they are not inconsistent with it.

Reproductive migration of the coconut crab Birgus latro

Knowledge of movement patterns is essential in tailoring spatial conservation and management measures. Although populations of the coconut crab, Birgus latro, have been severely depleted in most habitats, there have been few serious attempts to manage the resources. Recently, spatial conservation (e.g. seasonal area closure) has been suggested as an effective tool for resource management. However, relatively little is known about coconut crab movements, especially reproductive migration. To determine the dynamics of the reproductive migration of coconut crabs, we investigated both male and female migration patterns during the reproductive season in Hatoma Island, southwest of Japan. Both females and males migrated between inland and coastal areas during the reproductive season. Observed female seaward and landward migrations were temporally coincident with their reproductive activities (egg extrusion and larval hatching). Observed temporal-spatial distribution of males would be shaped by temporal variations in expected future mating opportunities within the reproductive season and male reproductive strategy in response to these variations.

Male and female reproductive strategies and multiple paternity in the polygynandrous Alpine Accentor Prunella collaris

Five breeding groups of the Alpine Accentor were studied in a Swiss alpine region. The studied groups showed a polygynandrous mating system and each group was formed of 1–4 females and 3–5 males. The females had exclusive territories, while the males cooperated in defending their group territory. Among the males of one group, a linear dominance relationship was usually well established among the alpha, beta and subordinate male S 1. Both frequent copulation and mate guarding strategies were applied. Females advertised their fertility, solicited most of the copulations and mated multiple times with several males. With approximately 350 matings during the short fertile period of 10 days, the Alpine Accentor is one of the bird species with the highest copulation frequency. Intensity of mate guarding and copulation frequency were highest starting 1 day before egg-laying and throughout the egg-laying period. The alpha male guarded a fertile female closely during the ovulation period, while the beta and other subordinate males (S 1, S 2 and S 3) were restricted in their access to fertile females by the alpha male’s mate guarding ability. In most cases, they did not guard mates and solely performed the frequent copulation strategy. Accordingly, higher ranking males got more solicitations from females, maintained a higher copulation frequency, but also refused a greater portion of all mating offers. Sperm competition was intense with 81.8 % of the broods having multiple paternity. The share of matings during the ovulation period best reflected the achieved share of paternity. Alpha, beta and S 1 sired most of the young, while S 2, S 3 and extra-group males were seldom fathers of offspring. At one nest, up to 4 males helped to feed the young, however, usually at a low rate and the overall male help (28 %) was smaller than the female contribution (72 %). In this polygynandrous mating system, females of the studied population lacked full male help but might have benefited from the greater genetic variation of their young, while males have a large individual variance in their lifetime reproductive success with higher ranking males raising their fitness to above average.

Positive Selection and the Evolution of izumo Genes in Mammals.

Most genes linked to male reproductive function have been known to evolve rapidly among species and to show signatures of positive selection. Different male species-specific reproductive strategies have been proposed to underlie positive selection, such as sperm competitive advantage and control over females postmating physiology. However, an underexplored aspect potentially affecting male reproductive gene evolution in mammals is the effect of gene duplications. Here we analyze the molecular evolution of members of the izumo gene family in mammals, a family of four genes mostly expressed in the sperm with known and potential roles in sperm-egg fusion. We confirm a previously reported bout of selection for izumo1 and establish that the bout of selection is restricted to the diversification of species of the superorder Laurasiatheria. None of the izumo genes showed evidence of positive selection in Glires (Rodentia and Lagomorpha), and in the case of the non-testes-specific izumo4, rapid evolution was driven by relaxed selection. We detected evidence of positive selection for izumo3 among Primates. Interestingly, positively selected sites include several serine residues suggesting modifications in protein function and/or localization among Primates. Our results suggest that positive selection is driven by aspects related to species-specific adaptations to fertilization rather than sexual selection.

Biology of a new species of socially parasitic thrips (Thysanoptera: Phlaeothripidae) inside Dunatothrips nests, with evolutionary implications for inquilinism in thrips

Akainothrips francisi sp. nov. is shown to be an inquiline (i.e. it invades, and breeds within, domiciles of another species). Currently, its only known host is Dunatothrips aneurae, a subsocial thrips that creates silken domiciles by securing together phyllodes of mulga (Acacia aneura) in the arid zone of Australia. We found Ak. francisi prolifically breeding inside live D. aneurae host domiciles, both immature and mature. Akainothrips francisi did not kill its host and we saw no evidence of antagonistic host-inquiline interactions. This is thus the second demonstrably inquiline species of Acacia thrips, although other possible inquilines have been suggested including two Akainothrips. We found that Ak. francisi occurred with positive density dependence, and was associated with moderately reduced host reproduction. This latter association was especially evident in larger host domiciles, suggesting that Ak. francisi either inhibits further host reproduction after invasion or exploits poor quality hosts more successfully. Sex ratios were slightly female biased. Akainothrips francisi males were exceptionally variable in size, colour, and foreleg size compared to females, with morphs co-occurring within domiciles, suggesting sexual selection and the possibility of different male reproductive strategies. The discovery of Ak. francisi highlights particular morphological affinities among known or suspected inquiline Acacia thrips within Akainothrips and other genera, allowing us to hypothesize a common origin of this lifestyle from within Akainothrips. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, , ••‐••. ADDITIONAL KEYWORDS: commensalism ‐ dealation ‐ eusociality ‐ Hymenoptera ‐ social parasitism ‐ subsociality.

Prolactin, fatherhood, and reproductive behavior in human males

Although humans are considered unusual among mammals for the intensity of care that fathers often provide offspring, little is known about the hormonal architecture regulating human paternal investment. Prolactin has important reproductive functions in both female and male mammals and other taxa, making it a candidate regulator of human paternal behavior. Notably, prolactin is higher during periods of offspring care in some species, but it is unknown if this pattern occurs in human fathers. We draw on a sample of men (n = 289; age 21-23 at baseline) from Metropolitan Cebu City, Philippines to evaluate relationships between prolactin, assayed from dried blood spots, and components of reproductive behavior and relationship status. In this sample, fathers had higher prolactin than nonfathers (P = 0.006), and fathers of infants had borderline higher prolactin than fathers of older children (P = 0.054). Among single nonfathers at baseline (2005), baseline prolactin did not predict who transitioned to fatherhood by follow-up 4.5 years later. Among nonfathers, men with greater prolactin reported more lifetime sexual partners (P = 0.050) as well as more sexual activity in the month before sampling (P = 0.060). Our results suggest that fathers in Cebu have higher prolactin than nonfathers, with hormone levels highest among fathers of young infants. Although these findings are generally consistent with evidence from other species for pronurturing effects of prolactin, evidence for positive relationships between the hormone and measures of sexual behavior at Cebu point to likely complexities in the hormone's involvement in male reproductive strategy.

The effect of isolation from conspecifics on spermatophore output of two species of eriophyoid mites

Eriophyoids are group-living, phytophagous mites whose males place spermatophores on a substrate, while females seek them out and perform self-insemination. Various factors, for example, rainfall, extreme temperatures and predatory mites, can considerably reduce the population size of eriophyoids which, simultaneously, may influence their reproductive strategies and output. In this study, the effect of a relatively short, 2-day absence of conspecifics on the spermatophore production of Aculus fockeui (Nalepa & Trouessart) and Aculops allotrichus (Nalepa) was examined. These species differ in male reproductive strategies. Both A. allotrichus and A. fockeui males can deposit spermatophores in the absence of quiescent female nymphs (QFNs). However, when QFNs are present, A. allotrichus males guard the nymphs from other males and deposit spermatophores beside them. In contrast, male A. fockeui rarely deposit spermatophores beside QFNs and do not interact with competitors. Previous tests have revealed that spermatophore output of eriophyoid males kept in isolation can differ significantly from output in the presence of conspecifics. In this study, on the second day of isolation, males of A. allotrichus significantly increased their rate of spermatophore deposition, whereas the coefficient of variation (CV) for spermatophore output considerably decreased. In A. fockeui, in contrast, both parameters were similar on both days. Moreover, no matter how many spermatophores the males of A. fockeui deposited on the first day, they produced a similarly high or low number on the second day (positive correlation between the two days). However, if on the first day male A. allotrichus deposited a relatively high number of spermatophores, on the second day they produced a relatively low number, or vice versa (negative correlation). All inter-specific discrepancies in spermatophore deposition during the absence of conspecifics are discussed in the context of differences in male reproductive strategies, as well as possible differences in male energy budgets and rhythms of spermatophore deposition between species.

Determinants of Natural Mating Success in the Cannibalistic Orb-Web Spider Argiope bruennichi

Monogynous mating systems (low male mating rates) occur in various taxa and have evolved several times independently in spiders. Monogyny is associated with remarkable male mating strategies and predicted to evolve under a male-biased sex ratio. While male reproductive strategies are well documented and male mating rates are easy to quantify, especially in sexually cannibalistic species, female reproductive strategies, the optimal female mating rate, and the factors that affect the evolution of female mating rates are still unclear. In this study, we examined natural female mating rates and tested the assumption of a male-biased sex ratio and female polyandry in a natural population of Argiope bruennichi in which we controlled female mating status prior to observations. We predicted variation in female mating frequencies as a result of spatial and temporal heterogeneity in the distribution of mature females and males. Females had a low average mating rate of 1.3 and the majority copulated only once. Polyandry did not entirely result from a male-biased sex-ratio but closely matched the rate of male bigamy. Male activity and the probability of polyandry correlated with factors affecting pheromone presence such as virgin females' density. We conclude that a strong sex ratio bias and high female mating rates are not necessary components of monogynous mating systems as long as males protect their paternity effectively and certain frequencies of bigyny stabilise the mating system.

Reproductive competition and fecal testosterone in wild male giant pandas (Ailuropoda melanoleuca)

The giant panda (Ailuropoda melanoleuca) is notoriously difficult to study in the wild, but its interesting reproductive ecology makes the effort worthwhile. Perhaps more than most species, the panda is energy-limited, which alters the cost/benefit analysis of its reproductive ecology. Using global positioning system/very high frequency radiocollars to locate mating aggregations, we used behavioral observations and fecal testosterone assays to gain insight into male panda reproductive effort and strategies, and test theories relating to reproductive competition. Male pandas initially competed fiercely for access to females that were about to be fertile, but once male competitive status was determined, aggression rates declined. Contact aggression was only observed during the first 2 days of mating aggregations; thereafter, it was replaced with noncontact aggression and avoidance. Agonistic interactions were highly asymmetrical, with contest losers (subordinates) showing less aggression and more avoidance than contest winners (dominants), both before and after contest outcome was established. The competitively superior male displayed mate-guarding tactics and secured all observed copulations. Contrary to theoretical predictions, testosterone levels did not predict aggression levels or contest winners and also were not affected by winning or losing a contest. Body size appeared to be the primary determinant of contest outcome. We discuss our findings in light of theoretical predictions, such as those arising from the “challenge hypothesis,” in the context of the giant panda’s foraging and nutritional ecology.

Mate competition, testosterone and intersexual relationships in bonobos, Pan paniscus

Variation in male testosterone levels across and within species is known to be related to mating systems, male dominance rank and aggression rates. When aggression enhances access to mates, dominance status and androgen levels correlate positively. Deviation from this pattern is expected when access to females is determined by factors other than male dominance or when high androgen levels interfere with nonaggressive forms of male reproductive strategies such as paternal care and pair bonding. Bonobos offer an interesting study species to test the relationship between male dominance, aggression and intersexual relationships. On the one hand, males form dominance hierarchies and compete for access to females and mating success varies with rank. On the other hand, males and females are equally dominant, male rank is not only the result of aggression, and strong intersexual relationships might be crucial to male reproductive success. We used behavioural and physiological data from wild bonobos to test relationships between behavioural correlates of mate competition and androgen levels. Aggression and rank were positively correlated, as were aggression and mating success. In the presence of potentially fertile females, male aggression increased but only low-ranking, less aggressive males showed increases in testosterone levels, which consequently tended to be negatively related to rank. High-ranking males who had lower testosterone levels and were less responsive in their testosterone increase were more often involved in friendly relationships with unrelated females. These results suggest that, in bonobos, amicable relationships between the sexes rather than aggressive interactions mediate males’ physiological reactivity during periods of mate competition.

Testing the role of male-male competition in the evolution of sexual dimorphism: a comparison between two species of porcelain crabs

Theory predicts marked sexual dimorphism in terms of body size and body structures used as weapons (e.g. chelipeds) in gonochoric species with intense male sexual competition for receptive females and reduced or no sexual dimorphism in species where competition among males is trivial. We tested this hypothesis using a pair of closely-related species of symbiotic porcelain crabs as a model. In one species that inhabits sea anemones solitarily, competition among males for receptive females is unimportant. In a second species that dwells as dense aggregations on sea urchins, male–male competition for sexual partners is recurrent. We expected considerable sexual dimorphism in body size and weaponry in the urchin-dwelling crab and reduced sexual dimorphism in the anemone-dwelling crab. In agreement with expectations, in the urchin-dwelling crab, male body size was, on average, larger than that of females and males invested considerably more to cheliped length than females. Also supporting theoretical considerations, in the anemone-dwelling crab, sexual dimorphism in terms of body size was not detected and differences between the sexes in investment to cheliped length were minor. Interestingly, chelipeds were more developed both in males and females of the anemone-dwelling crab than in the urchin-dwelling crab as a result of the importance of these structures for monopolization of their naturally scarce anemone hosts. Another difference between the studied species was the existence of two clearly distinguishable ontogenetic phases in males of the urchin-dwelling crab but not in males of the anemone-dwelling crab. Whether the two different male morphs display different male reproductive strategies in the urchin-dwelling crab remains to be addressed. Other conditions that might additionally explain the observed differences in sexual dimorphism (e.g. female mate choice) between the studied species remain to be explored. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 548–558.

Multiple Paternity in the Common Five-lined Skink (Plestiodon fasciatus)

Multiple mating and sperm storage can influence reproductive strategies of males and females. Male reproductive success is often limited by the ability to acquire mates; therefore, males have evolved strategies to mate with multiple females. In contrast, the number of offspring a female produces is generally not limited by the quantity of sexual partners; thus, selection for multiple matings is expected to be weaker than in males. Evidence of polyandry and sperm storage is widespread among lizards. We investigated whether female Common Five- lined Skinks (Plestiodon fasciatus) could store viable sperm between reproductive cycles, estimated the frequency of multiple paternity, and examined the sharing of paternity within clutches. Females were unable to store viable sperm between successive clutches. Most clutches (65%) had multiple sires, but within those clutches, there was unequal sharing of paternity. Although we cannot determine the function of polyandry from our data, we suggest possible causes of polyandry in the mating system of this species. Multiple mating by males and females has been well documented in numerous vertebrate and invertebrate taxa (Birkhead and Moller, 1998). Although widespread, the evolution of polyandry is more difficult to explain based on the existing literature than is polygyny. For males, mating opportunities are the most severe limitation of reproductive success, and accordingly, selection has driven male strategies toward the acquisition of multiple females (Andersson, 1994; Birkhead and Moller, 1998; Birkhead, 2000). In contrast, for females, a single mating typically can fertilize their ova and reproductive success is generally not constrained by the number of partners (Bateman, 1948; Trivers, 1972; but see Madsen et al., 1992).

Blood corticosterone levels and intersexual selection games: best-of-bad-job strategies of male common lizards

Glucocorticoids affect physiology and behaviour, reproduction and potentially sexual selection as well. Short-term and moderate glucocorticoid elevations are suggested to be adaptive, and prolonged and high elevations may be extremely harmful. This suggests that optimal reproductive strategies, and thus sexual selection, may be dose dependent. Here, we investigate effects of moderate and high elevations of blood corticosterone levels on intra- and intersexual behaviour and mating success of male common lizards Lacerta vivipara. Females showed less interest and more aggressive behaviour towards high corticosterone males and blood corticosterone levels affected male reproductive strategy. Males of moderate and high corticosterone elevations, compared with Control males, showed increased interest (i.e., higher number of chases, tongue extrusions, and approaches) towards females and high corticosterone males initiated more copulation attempts. However, neither increased male interest nor increased copulation attempts resulted in more copulations. This provides evidence for a best-of-a-bad-job strategy, where males with higher corticosterone levels compensated for reduced female interest and increased aggressive female behaviour directed towards them, by showing higher interest and by conducting more copulation attempts. Blood corticosterone levels affected intrasexual selection as well since moderate corticosterone levels positively affected male dominance, but dominance did not affect mating success. These findings underline the importance of female mate choice and are in line with adaptive compensatory behaviours of males. They further show that glucocorticoid effects on behaviour are dose dependent and that they have important implications for sexual selection and social interactions, and might potentially affect Darwinian fitness.