Polygynous Mating Research Articles

The influence of sexual selection and male agility on sexual size dimorphism in bustards (Otididae)

Bustards vary considerably in sexual size dimorphism (SSD), ranging from reversed-dimorphic species (i.e. male < female) through monomorphic species to species in which an adult male can be three times heavier than an adult female. We used this unusual interspecific variation to test functional hypotheses of SSD using phylogenetic comparative methods. We found a strong allometric relation between SSD and body size that is consistent with Rensch's rule. We then tested whether the intensity of mating competition and the agility of male displays relate to SSD. First, the intensity of mating competition hypothesis predicts that males should be larger than females in species in which the males compete intensely for mates. As predicted, evolutionary changes towards more polygynous mating systems in bustards were associated with relatively larger males. Second, our results are also consistent with the aerial agility hypothesis, since in agile bustards the males tend to be smaller than females, whereas in nonagile bustards the males are usually larger. We also found that these two types of sexual selection have independent and statistically significant influences on SSD. We conclude that SSD in bustards is most consistent with sexual selection, and is influenced by both the intensity of sexual selection and the agility of male displays. Other hypotheses, however, such as fertility selection acting on females and differential use of niches by males and females remain untested.

Males in the shade: habitat use and sexual segregation in the Galápagos sea lion (Zalophus californianus wollebaeki)

In many sexually dimorphic species adult sexes tend to segregate socially, spatially, or in habitat use. Several hypotheses have been formulated regarding underlying mechanisms. We investigated terrestrial habitat use and sexual segregation in a tropical otariid, the Galapagos sea lion (Zalophus californianus wollebaeki), where most of the hypotheses can be ruled out a priori. Factors relating to thermoregulation and costs of locomotion were of prime importance for habitat use. Habitats directly adjacent to the sea, with simple structured flat surfaces, shade, and tide pools were most frequented, but sexes and age classes differed in their usage patterns. Sexual segregation, both spatial and by habitat was pronounced in the reproductive period (RP), but remained high during the nonreproductive period (NRP). A GLM model of habitat use showed that in both seasons adult males frequented habitat types that adult females and other age classes used much less. Males were most abundant in suboptimal inland habitats, which offered only shade for cooling. Females with newborns differed in habitat use from females with older offspring and lone females. Spatial and habitat segregation are explained most parsimoniously as by-products of social processes, primarily intrasexual competition and female avoidance of male harassment, linked to the polygynous mating system.

Sex, equality, and growth

Abstract. We set up a model of economic and demographic long‐run development, where inequality in income and reproductive success (polygynous mating) plays a central role. The model generates a slow and gradual compression of the income gap between landholders and landless, together with rising levels of human capital. This process spurts at some stage, as society endogenously transits into sustained growth. Simultaneously, inequality in income and reproductive success drops; society becomes monogamous.

The multiple signals assessed by female satin bowerbirds: could they be used to narrow down females' choices of mates?

Female choice based on multiple male traits has been documented in many species but the functions of such multiple traits are still under debate. The satin bowerbird has a polygynous mating system in which males attract females to bowers for mating; females choose mates based on multiple aspects of males and their bowers. In this paper, we demonstrate that females use some cues to decide which males to examine closely and other cues to decide which males to mate with. Female visitation rates to bowers were significantly related to male size and the males' 'solitary' display rates, and, to a lesser extent, to the numbers of bower decorations. After controlling for female visitation rates, it was found that a male's mating success was significantly related to his size and the rate at which he 'painted' his bower with saliva and chewed up plant material.

Paternity in humpback whales, Megaptera novaeangliae: assessing polygyny and skew in male reproductive success

Mating system theory predicts that differences between the sexes in potential reproductive rate and an operational sex ratio skewed strongly towards males should result in intense male competition, polygynous mating and high variance in male reproductive success. Accordingly, humpback whales are thought to be polygynous with differences in reproduction among males related to alternative mating tactics. However, there is currently a lack of data on male reproductive success. We tested predictions regarding male reproductive success in humpback whales using molecular assessment of paternity in a population in the Mexican Pacific. Parentage analysis was conducted for 125 mother–calf pairs and a sample of 297 males using 13 microsatellite loci. Two separate analyses were conducted, based upon conservative and relaxed criteria for the assignment of paternity. In the conservative analysis, 40 paternities (32.5% of tested calves) were assigned among 33 males, whereas in the relaxed analysis, 62 paternities (49.6% of calves) were assigned among 51 males. Regardless of analysis, the distribution of male reproductive success deviated from a random mating model, with significantly larger than expected variance (conservative, P = 0.011; relaxed, P = 0.022), and significantly more than expected males siring three calves (conservative, P = 0.021; relaxed, P = 0.011). However, most successful males sired only one calf and no male was assigned more than three calves, so reproductive skew was not severe. Therefore we conclude that this population has a polygynous mating system, but without the large variation in male reproductive success expected by apparent skew in the operational sex ratio and degree of male competition for mates.

Evidence for sexy sons in European starlings (Sturnus vulgaris)

The “sexy son” hypothesis suggests that females obtain future fitness benefits from mating with polygynous males through the inheritance by their sons of traits contributing to mating success. We tested this hypothesis in the facultatively polygynous European starling (Sturnus vulgaris) in two ways. We first compared sons of monogynous and polygynous free-living males for their abilities in nest site acquisition and female-directed behaviors in controlled aviary tests. We then investigated eggs laid in monogynous and polygynous matings for concentrations of maternal steroid hormones that could affect behavioral differentiation of sons. Sons of polygynous fathers defended more nest boxes and produced more courtship song than sons of monogynous fathers. Mean concentrations of maternal androstenedione (A4), 5α-dihydrotestosterone (DHT), testosterone (T), and 17β-estradiol (E) in yolks were not affected by mating status. However, the within-clutch pattern of A4 depended on mating status, with higher concentrations in last than in first eggs of clutches of monogynous but not polygynous matings. These results suggest that (1) sons may inherit from their fathers behavioral qualities for the successful acquisition of nest sites and attraction of mates; (2) differential exposure to maternal steroid hormones during development in the egg is unlikely the cause of the behavioral differences between adult sons of monogynous and polygynous fathers; and (3) females adjust the within-clutch pattern of androgen to mating status, possibly in response to the expected contribution of their mate to nestling care.

Female multiple copulations among wild Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in Qinling, China

Mating strategies are the key to understanding both reproduction and evolution. The majority of the previous work on the mating strategies of the Sichuan snub-nosed monkey (Rhinopithecus roxellana), a polygynous species, has concentrated on the character of sexual behavior between heterosexual individuals, mating patterns, and the seasonality of mating and births in captivity 7] and in wild. The importance of multiple copulations of them, both wild and captivity, has so far been neglected. In this study we present some preliminary data on female multiple copulations among wild Sichuan snubnosed monkeys in the Qinling Mountains, attempting to explain the significance of this phenomenon. This study was carried out in the Yuhuangmiao region, located in Zhouzhi Nature Reserve on the northern slope of the Qinling Mountains, intermittently, from March 8, 2003 to May 22, 2004. Monkey groups were provisioned using apples, radishes, and corns at a stable feeding site three times per day (10:00 AM, 12:00 PM and 2:00 PM) during the observation. This manipulation was to coax the animals from a distance of 0.5 50 m. One male unit (OMU), such as the BaZiTou unit and LuoPan unit, as well as individual animals within each unit could be distinguished . We collected the sexual behavior data with the focal animal sampling and behavior sampling. During the observation period, there were 38 females and 6 males in our group. For each male unit, the total number of adult females and the sub-adult female fluctuates from 4 to 10. Only one male was traced as long as possible every day from dawn till dusk. Besides the focal male, we noted other males’ copulations as more as possible. The mating season was between late September and December in accordance with previous authors. A total of 733 hours of observations were conducted from March 2003 to May 2004. During this period a total of 399 copulations (Table 1), including 22 multiple copulations (Table 2), were observed. Table 2 shows that: (i) female multiple copulations occurred throughout the year but were more frequent during the mating season than the non-mating season; (ii) the number of female multiple copulations per hour ranged from two to five; (iii) the mean duration of female multiple copulations per hour were greater in the mating season (19.67±1.29 s, n=17) than in the non-mating season (9.8±2.46 s, n=5); the difference in the mean duration of female multiple copulations between mating season and non-mating season was very significant (t=3.62, p=0.0008<0.01, t-test); and (iv) during the mating season both adult and sub-adult females were the main initiators to display the typical sexual behavior of multiple copulations, whereas during the non-mating season males become the primary initiators. Sperm competition is less important since usually only a single adult male is present in the polygynous mating system. In these cases, sperm might be a “limiting resource” for females within the one-male group, and female-female competition for conceptions might occur consequentially. As for the Sichuan snub-nosed monkey (Rhinopithecus roxellana), we suggest that multiple copulations initiated by females support the Small’s viewpoint that females might compete for the limited sperm reserves available, while behaviours of male Sichuan snub-nosed monkeys show their attitude about sperm allocations to some extent. In the present study, all adult females involved in multiple copulations during the mating season of 2003 gave birth between March and April of the next year 2004 while those not involved in multiple copulations did not gave birth. This suggests that by increasing the incidence of multiple copulations in the mating seasons female monkeys aim to increase the possibility of impregnations. These results are consistent with those of Andreas. Andreas pointed out that females benefited from multiple copulations via the assurance of fertility.

Assessment in contests of male lizards ( Anolis carolinensis): how should smaller males respond when size matters?

Within a female-defence polygynous mating system, males of the lizard A. carolinensis use an array of stereotyped signals and aggressive tactics to acquire and defend long-term territories containing multiple, sedentary females. In competition, body size appears to be important because size of free-ranging males correlates positively with volume of male territories and number of patrolled females. Therefore, an ability to assess body size during territorial contests should be an adaptive attribute that would influence the tactics of intermale aggression. To examine this premise, we staged contests between 10 pairs of males matched for size (i.e. symmetric contests) and 10 pairs mismatched for size (i.e. asymmetric contests), while all 20 pairs of males were matched for habitat resources, a mate, and resident status. Overall, we found (1) contest profiles best fit the features of a ‘fixed-phase, sequential assessment’ model of game theory, (2) body size and mass were highly correlated with contest outcome, (3) none of 12 signal variables predicted contest outcome, and (4) paired males generally matched aggressive tactics and signalling behaviours. We also examined the asymmetric contest profiles for deviations from the profiles of symmetric contests. We tested the proposition that smaller males of size-mismatched contests would assess their disadvantage and choose a bluff strategy to mitigate risky behaviour and avoid fighting. We found, however, that the risk-mitigation hypotheses were unsupported. Smaller males were not playing a bluff strategy, but rather a hawk strategy. They initiated risky tactics by (1) invading the habitats of their larger opponents, an act that invited retaliation, (2) showing no tendency to stay away from larger opponents, (3) maintaining high levels of aggressive signalling as encounters intensified, and (4) engaging larger opponents in physical fighting, despite losing 90% of their encounters. These empirical results support a recent game theoretical construct (‘Napoleon complex’) that models size-asymmetric contests in which smaller males initiate fights that they usually lose. Our data suggest that, if smaller males of A. carolinensis have breeding territories, then they will engage in costly contests, despite a low probability of defeating larger and equally motivated opponents.

SOLITARY ADULT MALES IN A POLYGYNOUS-MATING BAT (CYNOPTERUS SPHINX): A FORCED OPTION OR A STRATEGY?

Abstract The Indian short-nosed fruit bat (Cynopterus sphinx) is thought to use a resource-based polygynous mating system. Breeding colonies typically consist of a few harems with 1 or more solitary males nearby. Essential to understanding the mating system of C. sphinx is identification of the reasons for solitary roosting behavior in adult males. In this study, we attempt to elucidate the impetus behind solitary roosting by investigating the following 2 questions: Are solitary males less competitive and so remain isolated from breeding activities? Are trees and foliage suitable for tent-making a scarce resource? We carried out weekly censuses and mark–recapture studies from January to December 2000. We assessed impact of available resources on roosting patterns of adult males. Examination of our results suggests the following about the mating system of these bats. Female aggregation in C. sphinx cannot be attributed to scarce resources. Morphological variables did not differ between harem and nonharem m...

Big mothers invest more in daughters – reversed sex allocation in a weakly polygynous mammal

AbstractHow mothers allocate resources to offspring is central to understanding life history strategies. High quality mothers are predicted to favour investment in sons over daughters when to do so increases inclusive fitness. This is the case in ungulates with polygynous mating systems, where reproductive success is more variable among males than females, but information is scarce on sex allocation in less polygynous species. Here, for the weakly dimorphic roe deer, we show that as maternal capacity to invest increases, mothers increase allocation to daughters more than to sons, so that relative allocation to daughters increases markedly with increasing maternal quality. This cannot be explained by a between sex difference in growth priority, hence we conclude that this is evidence for active maternal discrimination. Further, we demonstrate that condition differences between offspring persist to adulthood. For high quality mothers of weakly polygynous species, daughters may be more valuable than sons.

Complex mating system and dispersal patterns in a social lizard,Egernia whitii

In contrast to the polygynous mating systems typically displayed by most reptilian taxa, long-term genetic monogamy appears to be widespread within a lineage of group-living Australian scincid lizards, the Egernia group. We have recently shown that White's skink, Egernia whitii, lives in small but temporally stable social aggregations. Here, we examine the mating system, spatial organization, and dispersal patterns of E. whitii using behavioural field studies and data from four microsatellite loci. Parentage analysis of E. whitii litters revealed that its mating system is characterized by both polygyny and monogamy. Polygyny was the predominant mating system but within-season social and genetic monogamy was common (36-45% of breeding pairs). The incidence of between-season monogamy in E. whitii was rare compared to that reported for its congeners. Low levels of multiple paternity (12% of litters) and extra-group paternity (16%) were detected. Social groups are generally comprised of closely related individuals, but breeding pairs were not more closely related compared to other potential mates. Spatial autocorrelation analyses revealed significant positive local genetic structure over 50 m, which was consistent for all age-sex classes. There was no clear and consistent evidence for sex-biased dispersal, with assignment tests (mean assignment index) and relatedness analyses suggesting female-biased dispersal, but spatial autocorrelation analyses indicating a trend for male-biased dispersal. We discuss the implication of our results in regard to the factors promoting the evolution of monogamy within the Egernia group.

Sexual Selection and the Evolution of Visually Conspicuous Sexually Dimorphic Traits in Male Monkeys, Apes, and Human Beings

Striking secondary sexual traits, such as brightly colored "sexual skin," capes of hair, beards, and other facial adornments occur in adult males of many anthropoid primate species. This review focuses upon the role of sexual selection in the evolution of these traits. A quantitative approach is used to measure sexually dimorphic characters and to compare their development in the monogamous, polygynous, and multimale-multifemale mating systems of monkeys, apes, and human beings.

Spatial organization of the honey badgerMellivora capensisin the southern Kalahari: home‐range size and movement patterns

Radio-tracking locations of 25 individuals (13 females; 12 males) and visual observations of nine habituated individuals were used to investigate the spatial organization and movement patterns of the honey badger Mellivora capensis in the southern Kalahari. The home ranges of adult male honey badgers (541 ± 93 km2) were significantly larger than the home ranges of adult females (126 ± 13 km2). Female home-range size was five times larger than predicted from body mass. The extensive home ranges of females were likely to be a function of relatively low prey availability in the semi-arid Kalahari and the long period of cub dependence (12–16 months). While mean home-range overlap in females was moderate (13%) and home-range centres were regularly spaced, females did not appear to actively defend a territory and no direct interactions between females were observed. Scent marking appears to mediate spatio-temporal separation and females show a loosely territorial spacing pattern. In contrast, males did not support the typical mustelid pattern of intra-sexual territoriality but instead encompassed the overlapping home ranges of up to 13 females. Males and females differed significantly in their rate of travel (3.8 ± 0.3 km/h vs 2.7 ± 0.2km/h), straight line (6.2 ± 0.5 km vs 2.4 ± 0.2 km) and actual distance (13.8 ± 0.9 km vs 7.7 ± 0.7 km) moved during an active period but do not differ in the percentage of their home-range area traversed in a single day (3%). Young males tended to have smaller home ranges (151 ± 45 km2) than adult males and showed a spacing pattern more similar to adult females than adult males. In common with other solitary mustelids, the spatial organization suggests a polygynous or promiscuous mating system.

Estimation of genetically effective breeding numbers using a rejection algorithm approach.

Polygynous mating results in nonrandom sampling of the adult male gamete pool in each generation, thereby increasing the rate of genetic drift. In principle, genetic paternity analysis can be used to infer the effective number of breeding males (Nebm). However, this requires genetic data from an exhaustive sample of candidate males. Here we describe a new approach to estimate Nebm using a rejection algorithm in association with three statistics: Euclidean distance between the frequency distributions of maternally and paternally inherited alleles, average number of paternally inherited alleles and average gene diversity of paternally inherited alleles. We quantify the relationship between these statistics and Nebm using an individual-based simulation model in which the male mating system varied continuously between random mating and extreme polygyny. We evaluate this method using genetic data from a natural population of highly polygynous fruit bats (Cynopterous sphinx). Using data in the form of mother-offspring genotypes, we demonstrate that estimates of Nebm are very similar to independent estimates based on a direct paternity analysis that included data on candidate males. Our method also permits an evaluation of uncertainty in estimates of Nebm and thus facilitates inferences about the mating system from genetic data. Finally, we investigate the sensitivity of our method to sample size, model assumptions, adult population size and the mating system. These analyses demonstrate that the rejection algorithm provides accurate estimates of Nebm across a broad range of demographic scenarios, except when the true Nebm is high.

Monogamy: Mating Strategies and Partnerships in Birds, Humans and Other Mammals

U. H. Reichard, C. Boesch (eds.). 2003. Monogamy: Mating Strategies and Partnerships in Birds, Humans and Other Mammals. Cambridge University Press, Cambridge, United Kingdom, 267 pp. ISBN 0-521-52577-2, price (paper), $45.00. Understanding the evolution of monogamy in mammals has challenged behavioral ecologists for decades, because in most cases males are predicted to experience higher fitness through polygynous mating. In contrast to birds, gestation and lactation limit the potential fitness benefits of paternal care for all but a handful of species. Individuals that live in monogamous pairs but mate with extra-pair partners present an additional puzzle. Monogamy: Mating Strategies and Partnerships in Birds, Humans and Other Mammals brings together the most recent comparative analyses and long-term field studies that address the evolution of monogamy in mammals. A book-length review of this topic is very welcome. The conceptual framework for thinking about mating systems in mammals for nearly a decade and a half (Clutton-Brock 1989; Davies 1991) has been rooted in Kleiman's (1977) seminal review of monogamy and Emlen and Oring's (1977) ecological framework of mating system evolution. These reviews overemphasized the role of parental care, now believed to have evolved after the evolution of monogamy in most cases, and de-emphasized the role of female choice in favor of male control of female reproduction. The advent of molecular techniques for parentage assignment has ushered in a new understanding of the costs and benefits of monogamy for individuals that …

Competing females and caring males. Sex steroids in African black coucals, Centropus grillii

The black coucal is the only known altricial bird species in which females mate with and lay eggs for more than one male and males are responsible for all parental care (classical polyandry). In this species, the left testis is atrophied and it has been speculated that this may result in a reduction of circulating androgens, providing a unique mechanism for reversals in sex roles. We therefore investigated whether there is a reversal in circulating androgens and oestrogens in black coucals. Despite the reversals in sex roles, males had significantly higher levels of plasma testosterone than females, in a pattern typical of that of monogamous male passerines. Testosterone levels of both sexes were higher during the mating than during the premating stage and were low in males during the nestling stage. The concentrations of androstenedione, dehydroepiandrosterone and oestradiol did not differ between the sexes and were generally low. A physiological challenge with gonadotropin-releasing hormone (GnRH) resulted in a significant increase in testosterone in males but not in females, suggesting either that females are not responsive to GnRH or that they express patterns of testosterone that are similar to those of males of species with a polygynous mating system without paternal care, in which testosterone is expressed at maximum levels throughout the breeding season. We conclude that the absence of one testis does not provide a mechanism for sex role reversal in black coucals. Either androgens are not involved in the regulation of male-like traits in females or females are sensitive to relatively low levels of these steroids.

Time to extinction in relation to mating system and type of density regulation in populations with two sexes

Summary Population viability models usually consider only the female segment of the population. However, random variation in sex ratio as well as the mating system may also affect variation in fitness among females. Here we develop population models incorporating demographic stochasticity in both sexes. Furthermore, we consider the effects on the estimated time to extinction and whether density regulation acts only on females or on total population size. We applied these models to two populations of polygynous great reed warblers Acrocephalus arundinaceus L. with differences in population trends to investigate the importance of considering sex in population viability models. Demographic stochasticity was larger in a polygynous than in a monogamous mating system. The estimated time to extinction was considerably shorter for a monogamous than for a polygynous mating system, particularly if density regulation acted only on females than rather on the total population. This study demonstrates that structure of mating system must be included when making population viability analysis based on counts of total population sizes. It is especially important to model the specific effects of density regulation on the two sexes.

Field studies on a social lizard: Home range and social organization in an Australian skink, Egernia major

Abstract Although most reptiles have polygynous mating systems without long‐term pair bonds, one lineage of large scincid lizards in Australia is exceptional in this respect. Reports of complex sociality in the genus Egernia led us to conduct the first radiotelemetric field study of a species within this group. Land mullets (Egernia major) are large (60 cm total length), viviparous lizards from rainforest habitats in south‐eastern Australia. To document the spatial ecology and social organization of this species, we captured 12 adult lizards in the Barrington Tops area of eastern New South Wales and implanted them with miniature radiotransmitters. The lizards were released at their sites of capture and located daily for the next 6 weeks. All of the radiotracked lizards had discrete home ranges of approximately 10 000 m2, based around well‐defined core areas (approximately 2000–3000 m2). Females tended to move further, and to range over wider areas, than did males. All of the radiotracked lizards lived in social groups consisting of one or more adult males and females plus juveniles of all age classes. Subgroups were apparent within one group of five radio‐tagged lizards: individual animals consistently shared their shelter sites and home ranges with one or more specific individuals. Male/female pairings were more frequent than expected under the null hypothesis of random association among individuals. The data in the present study support anecdotal reports of pair bonds in E. major and support suggestions that the social systems of species in this genus are more complex than those of previously studied reptiles.

Monogamy in marine fishes.

The formation of long-term pair bonds in marine fish has elicited much empirical study. However, the evolutionary mechanisms involved remain contested and previous theoretical frameworks developed to explain monogamy in birds and mammals are not applicable to many cases of monogamy in marine fish. In this review, we summarise all reported occurrences of social monogamy in marine fish, which has so far been observed in 18 fish families. We test quantitatively the role of ecological and behavioural traits previously suggested to be important for the evolution of monogamy and show that monogamous species occur primarily in the tropics and are associated with coral reef environments in which territory defence and site attachment is facilitated. However, there is little evidence that obligately monogamous species are smaller in body size than species that can adopt a polygynous mating system. We review the evidence pertaining to six hypotheses suggested for the evolution of monogamous pair bonds: (1) biparental care, (2) habitat limitation, (3) low population density/low mate availability/low mobility, (4) increased reproductive efficiency, (5) territory defence, and (6) net benefit of single mate sequestration. We outline predictions and associated empirical tests that can distinguish between these hypotheses, and assess how generally each hypothesis explains monogamy within and between breeding periods for species with different types of territories (i.e. feeding only or feeding and breeding). Hypotheses (1) and (2) have limited applicability to marine fishes, while hypotheses (3)-(5) have little empirical support beyond the species for which they were designed. However, the role of paternal care in promoting monogamous pair bonds is not explicit in these hypotheses, yet paternal care has been reported in more than 70 monogamous marine fish. We show that paternal care may act to increase the likelihood of monogamy in combination with each of the proposed hypotheses through decreased benefits to males from searching for additional mates or increased advantages to females from sequestering a single high-quality mate. Among species defending breeding and feeding territories, the benefits, both within and between reproductive periods, of sequestering a single high-quality mate (hypothesis 6) appear to be the best explanation for socially monogamous pairs. For species without parental care (i.e. holding only feeding territories), territory defence (hypothesis 5) in combination with the benefits of guarding a large mate (hypothesis 6) could potentially explain most instances of monogamy. Empirical studies of marine fishes over the past two decades are therefore slowly changing the view of monogamy from a mating system imposed upon species by environmental constraints to one with direct benefits to both sexes.

Polygynous mating impairs body condition and homeostasis in male reindeer ( Rangifer tarandus tarandus )

Reindeer are polygynous ruminants that breed when plant growth declines in the Arctic. We studied seven males (2 years and older) in two herds with a total of 34 females to describe the costs and consequences of mating or rut. Body mass declined between September and November and did not recover through winter even though food was available ad libitum. Dominance did not affect body mass or any correlate of mass loss, indicating similar costs of rut among males. Males lost 34% of ingesta-free mass in 77 days of rut, which corresponded to depletion of 23% body protein and 78% body lipid. Water flux, plasma insulin, and plasma thyroxine were minimal 23 days after the peak in body mass, indicating low food intake. Maximum plasma testosterone and cortisol also followed peak mass and coincided with the death of two males from acute infections. Loss in body protein did not increase the ratio of urea to creatinine in plasma. Increased variance in plasma osmolality and urea during mass loss indicated altered homeostatic control during rut. Mating compromises survival of males through reduction of body reserves, food intake, and maintenance of tissues. These adverse effects may be the consequence of selection for large body size and aggression in a highly variable competition for mates.