Genetic mating system and mate selection in smallmouth bass

Mating systems are an important factor influencing the variance in reproductive success among individuals within natural populations and thus have important ecological and evolutionary implications. We used molecular pedigree reconstruction techniques with microsatellite DNA data to characterize the genetic mating system and mate selection in adult smallmouth bass spawning in Lake Opeongo. The genetic mating system of smallmouth bass in this system can be characterized as predominantly monogamous with a low rate of polygynandry particularly among larger individuals. Iteroparous individuals showed a complete absence of interannual mate fidelity, presumably due to the low annual return rate of spawning adults. Within a season, individuals from both sexes pursued additional mating opportunities with males showing greater variance in mate number than females. Female mate selection appeared to be largely random with little evidence for elevated levels of inbreeding in this population. Multiple mating females pursued additional males to whom they were less related than the first male with which they spawned within a given season, however, this pattern varied among years. The mating pattern observed in this population would likely limit the strength of sexual selection and thus could account for the lack of sexual dimorphism and the absence of alternative reproductive tactics in this species.     

Male and Female Soldier Beetles Relax Choice for Mate Quality Across Daily Courtship Periods

Mutual mate choice occurs when members of each sex will reject some potential mates in efforts to encounter better prospects later. The decision to reject may represent the interaction between mate preferences, mate availability, and temporal constraints. Theory predicts that mutual mate choice will favor relaxed choosiness as mate availability and time for courtship decline. We explored mutual mate choice in the soldier beetle, Chauliognathus pennsylvanicus (Cantharidae), where courtship consisted of males attempting to secure evasive females. We employed field observations, laboratory experiments, and stochastic simulations to investigate the decline in choosiness over the daily courtship period, during which individuals can mate at most once. We found that reproductive success of males and females increases with mate size and mating frequency. Females biased copulations toward larger mates by attempting to evade suitors, while males biased copulations by releasing the smaller females they capture. However, late in the day males and females may increase reproductive success by accepting rather than rejecting lower quality mates to maintain high mating rates. Stochastic simulations indicated that reproductive success, the product of mating frequency and mean mate size, was maximized in males and females by incrementally reducing mate standards across daily courtship periods. In the field, large males who rejected small females early in the daily courtship period rarely did so later. Large females used less effective evasive maneuvers later in the courtship period, resulting in copulations with progressively smaller males. These results support models of mutual mate choice that predict that individuals of high quality will maximize reproductive success by relaxing choosiness as the courtship period wanes.     

Variation in selection pressure acting on body size by age and sex in a reverse sexual size dimorphic raptor

Body size strongly influences fitness, with larger individuals benefiting in terms of both greater productivity and survivorship; for reverse sexual size dimorphic (RSD) species, this relationship may be more complex. We examined the selection pressures acting on body size in male and female Merlins Falco columbarius to assess whether larger or smaller individuals of this RSD species were favoured in terms of survival and breeding performance. For males and females there were clear links between body size and survival but the exact relationship varied by sex. Among males, birds that survived each year class were larger than those that died and yearlings were on average smaller than older birds, but there were no measurable differences among adult males (age 2+). Among females, larger individuals aged 1 and 2 years were more likely to survive, but this size‐based pattern was not apparent in older age classes. Size early in life predicted the lifespan in male Merlins but not as strongly as for females and not for the largest individuals. Reproductive performance based on brood size was not associated with body size in either males or females, but there was a weak positive relationship between female body size and lifetime reproductive success. Selection appears to favour larger males and females but there is no indication that the population is evolving towards bigger individuals, perhaps in part due to selection against the largest birds. Increased survival may allow larger and higher quality individuals to occupy higher quality territories as they age and thereby to accrue greater lifetime reproductive success in the process.     

Genetic analysis of the mating system and opportunity for sexual selection in northern water snakes (Nerodia sipedon)

We used data collected over 3 years at two study sites to quantifythe rates and consequences of multiple paternity and to determinethe opportunity for selection on male and female northern watersnakes (Nerodia sipedon). We sampled litters from 45 femalesthat gave birth to 811 offspring. Using eight microsatelliteDNA loci (probability of exclusion of nonparental males >0.99), we assigned paternity to 93% of neonates from one studypopulation and 69% of neonates from the other population. Observationsof participation in mating aggregations predicted individual reproductive success poorly for two reasons. First, males regularlycourted nonreproductive females. Second, more than half ofall sexually mature males obtained no reproductive successeach year, despite the fact that many of them participatedin mating aggregations. The number of sires per litter ranged from one to five, with 58% of all litters sired by more thanone male. Multiple paternity increased with female size, apparentlyboth because bigger females mated with more males and becausethe larger litters of big females provide paternity opportunitiesto more males. Multiple paternity was also more prevalent inyears with shorter mating seasons. We detected no advantage to multiple paternity in reducing either the number of unfertilizedovules or stillborn young. Despite the majority of males siringno young each year, some males fathered young with as manyas three different females in one year. Male reproductive successincreased by more than 10 offspring for each additional mate,whereas female success increased by fewer than 2 offspring foreach additional mate. The opportunity for sexual selectionwas more than five times higher in males than females.     

Field evidence challenges the often‐presumed relationship between early male maturation and female‐biased sexual size dimorphism

Female‐biased sexual size dimorphism (SSD) is often considered an epiphenomenon of selection for the increased mating opportunities provided by early male maturation (i.e., protandry). Empirical evidence of the adaptive significance of protandry remains nonetheless fairly scarce. We use field data collected throughout the reproductive season of an SSD crab spider, Mecaphesa celer, to test two hypotheses: Protandry provides fitness benefits to males, leading to female‐biased SSD, or protandry is an indirect consequence of selection for small male size/large female size. Using field‐collected data, we modeled the probability of mating success for females and males according to their timing of maturation. We found that males matured earlier than females and the proportion of virgin females decreased abruptly early in the season, but unexpectedly increased afterward. Timing of female maturation was not related to clutch size, but large females tended to have more offspring than small females. Timing of female and male maturation was inversely related to size at adulthood, as early‐maturing individuals were larger than late‐maturing ones, suggesting that both sexes exhibit some plasticity in their developmental trajectories. Such plasticity indicates that protandry could co‐occur with any degree and direction of SSD. Our calculation of the probability of mating success along the season shows multiple male maturation time points with similar predicted mating success. This suggests that males follow multiple strategies with equal success, trading‐off access to virgin females with intensity of male–male competition. Our results challenge classic hypotheses linking protandry and female‐biased SSD, and emphasize the importance of directly testing the often‐assumed relationships between co‐occurring animal traits.     

An integrative mating system assessment of a nonmodel,economically important Pacific rockfish (Sebastes melanops) reveals nonterritorial polygamy and conservation implications for a large species flock

Characterizing the mating systems of long‐lived, economically important Pacific rockfishes comprising the viviparous Sebastes species flock is crucial for their conservation. However, direct assignment of mating success to sires is precluded by open, offshore populations and high female fecundity. We addressed this challenge by integrating paternity‐assigned mating success of females with the adult sex ratio (ASR) of the population, male evolutionary responses to receptive females, and reproductive life history traits—in the framework of sexual selection theory—to assess the mating system of Sebastes melanops. Microsatellite parentage analysis of 17 pregnant females, 1,256 of their progeny, and 106 adults from the population yielded one to four sires per brood, a mean of two sires, and a female mate frequency distribution with a truncated normal (random) pattern. The 11 multiple paternity broods all contained higher median allele richness than the six single paternity broods (Wilcoxon test: W = 0, p < .001), despite similar levels of average heterozygosity. By sampling sperm and alleles from different males, polyandrous females gain opportunities to enhance their sperm supply and to lower the cost of mating with genetically incompatible males through reproductive compensation. A mean of two mates per mated female with a variance of one, an ASR = 1.2 females per male, and the expected population mean of 2.4 mates for mated males (and the estimated 35 unavailable sires), fits polygamous male mate frequency distributions that distinguish polygynandry and polyandrogyny mating systems, that is, variations of polygamy, but not polyandry. Inference for polygamy is consistent with weak premating sexual selection on males, expected in mid‐water, schooling S. melanops, owing to polyandrous mating, moderately aggregated receptive females, an even ASR, and no territories and nests used for reproduction. Each of these characteristics facilitates more mating males and erodes conspicuous sexual dimorphism. Evaluation of male evolutionary responses of demersal congeners that express reproductively territorial behavior revealed they have more potential mechanisms for producing premating sexual selection, greater variation in reproductive success, and a reduced breeding effective population size of adults and annual effective size of a cohort, compared to S. melanops modeled with two mates per adult. Such divergence in behavior and mating system by territorial species may differentially lower their per capita birth rates, subsequent population growth, and slow their recovery from exploitation.     

Experimental evidence that female ornamentation increases the acquisition of sperm and signals fecundity

Mate choice can lead to the evolution of sexual ornamentation. This idea rests on the assumption that individuals with more elaborate ornaments than competitors have higher reproductive success due to gaining greater control over mating decisions and resources provided by partners. Nevertheless, how the resources and quality of sexual partners that individuals gain access to are influenced by the ornamentation of rival individuals remains unclear. By experimentally concealing and subsequently revealing female ornaments to males, we confirm in the fowl, Gallus gallus, that female ornamentation influences male mating decisions. We further show, by manipulating the relative ornament size of females, that when females had larger ornaments than competitors they were more often preferred by males and obtained more sperm, especially from higher quality males, as measured by social status. Males may benefit by investing more sperm in females with larger ornaments as they were in better condition and produced heavier eggs. Female ornament size also decreased during incubation, providing a cue for males to avoid sexually unreceptive females. This study reveals how inter-sexual selection can lead to the evolution of female ornaments and highlights how the reproductive benefits gained from mate choice and bearing ornaments can be dependent upon social context.     

Female‐biased size dimorphism in a diapausing caddisfly,Mesophylax aspersus: effect of fecundity and natural and sexual selection

1. The effect of mating success, female fecundity and survival probability associated with intra‐sex variation in body size was studied in Mesophylax aspersus, a caddisfly species with female‐biased sexual size dimorphism, which inhabits temporary streams and aestivates in caves. Adults of this species do not feed and females have to mature eggs during aestivation. 2. Thus, females of larger size should have a fitness advantage because they can harbour more energy reserves that could influence fecundity and probability of survival until reproduction. In contrast, males of smaller size might have competitive advantages over others in mating success. 3. These hypotheses were tested by comparing the sex ratio and body size of individuals captured before and after the aestivation period. The associations between body size and female fecundity, and between mating success and body size of males, were explored under laboratory conditions. 4. During the aestivation period, the sex ratio changed from 1 : 1 to male biased (4 : 1), and a directional selection on body size was detected for females but not for males. Moreover, larger clutches were laid by females of larger size. Finally, differences in mating success between small and large males were not detected. These results suggest that natural selection (i.e. the differential mortality of females associated with body size) together with possible fecundity advantages, are important factors responsible of the sexual size dimorphism of M. aspersus. 5. These results highlight the importance of taking into account mechanisms other than those traditionally used to explain sexual dimorphism. Natural selection acting on sources of variation, such as survival, may be as important as fecundity and sexual selection in driving the evolution of sexual size dimorphism.     

Sexual selection and mating patterns in a mammal with female-biased sexual size dimorphism

In mammals, species with highly male-biased sexual size dimorphismtend to have high variance in male reproductive success. However,little information is available on patterns of sexual selection,variation in male and female reproductive success, and bodysize and mating success in species with female-biased size dimorphism.We used parentage data from microsatellite DNA loci to examinethese issues in the yellow-pine chipmunk (Tamias amoenus), asmall ground squirrel with female-biased sexual size dimorphism.Chipmunks were monitored over 3 years in the Kananaskis Valley,Alberta, Canada. We found evidence of high levels of multiplepaternity within litters. Variation in male and female reproductivesuccess was equal, and the opportunity for sexual selectionwas only marginally higher in males than females. Male and femalereproductive success both depended on mating success. We foundno evidence that the number of genetic mates a male had dependedon body size. Our results are consistent with a promiscuousmating system in which males and female mate with multiple partners.Low variation in male reproductive success may be a generalfeature of mammalian species in which females are larger thanmales.     

Indirect mate choice, direct mate choice and species recognition in a bower-building cichlid fish lek

Sexual selection arising through female mate choice typically favours males with larger, brighter and louder signals. A critical challenge in sexual selection research is to determine the degree to which this pattern results from direct mate choice, where females select individual males based on variation in signalling traits, or indirect mate choice, where male competition governs access to reproductively active females. We investigated female mate choice in a lekking Lake Malawi cichlid fish, Hemitilapia oxyrhynchus, in which males build and aggressively defend sand 'bowers'. Similar to previous studies, we found that male reproductive success was positively associated with bower height and centrality on the lek. However, this pattern resulted from males holding these territories encountering more females, and thus their greater success was due to indirect mate choice. Following initial male courtship, an increase in the relative mating success of some males was observed, but this relative increase was unrelated to bower size or position. Crucially, experimentally manipulating bowers to resemble those of a co-occurring species had no appreciable effect on direct choice by females or male spawning success. Together, these results suggest indirect mate choice is the dominant force determining male-mating success in this species, and that bowers are not signals used in direct mate choice by females. We propose that, in this species, bowers have a primary function in intraspecific male competition, with the most competitive males maintaining larger and more central bowers that are favoured by sexual selection due to higher female encounter rates.     

The sex lives of parasites: Investigating the mating system and mechanisms of sexual selection of the human pathogen Schistosoma mansoni

The mating systems of internal parasites are inherently difficult to investigate although they have important implications for the evolutionary biology of the species, disease epidemiology, and are important considerations for control measures. Using parentage analyses, three topics concerning the mating biology of Schistosoma mansoni were investigated: the number of mates per adult male and female, variance in reproductive success among individuals, and the potential role for sexual selection on male body size and also mate choice for genetically dissimilar individuals. Results indicated that schistosomes were mostly monogamous, and evidence of only one mate change occurred over a period of 5-6 weeks. One male was polygynous and contained two females in its gynecophoral canal although offspring were only detected for one of the females. Even though they were primarily monogamous and the sex ratio near even, reproductive success was highly variable, indicating a potential role for sexual selection. Male body size was positively related to reproductive success, consistent with sexual selection via male-male competition and female choice for large males. However, relatedness of pairs was not associated with their reproductive success. Finally, genetically identical individuals differed significantly in their reproductive output and identical males in their body size, indicating important partner and environmental effects on these traits.     

The relation between male body size, fighting, and mating success in Dawson's burrowing bee, Amegilla dawsoni (Apidae, Apinae, Anthophorini)

Males of the bee Amegilla dawsoni (Anthophorini) vary greatly in size, with some of the largest individuals as large as the largest females, a rare phenomenon in insects. The occurrence of unusually large males appears to be the product of sexual selection for fighting ability. As predicted from this hypothesis: (1) males regularly competed aggressively to be in the best position to mount sexually receptive, virgin females as they emerged from the ground; (2) larger males usually won fights for potential mates, as demonstrated by the fact that males able to defend sites with an emerging female were larger on average than males they kept at bay; (3) the fighting advantage of large males translated into greater mating success. Males captured while mounted on a female were significantly larger on average than randomly captured matesearching males in two of three populations sampled in 1993. Moreover, males known to mate more than once were consistently larger than single-mating males in the 10 samples taken from four populations examined in 1994. Thus, a large male mating advantage applies across years and among populations, making it potentially advantageous for females of Dawson's burrowing bees to produce large, superior fighting sons about the same size as their daughters.     

First evidences of sexual selection by mate choice in marine zooplankton

Sexual selection is potentially important in marine zooplankton, presumably the most abundant metazoans on earth, but it has never been documented. We examine the conditions for sexual selection through mate choice and describe mating preferences in relation to size in a marine zooplankter, the pelagic copepod Acartia tonsa. Males produce spermatophores at a rate (~1 day⁻¹) much lower than known female encounter rates for most of the year and the decision to mate a particular female thus implies lost future opportunities. Female egg production increases with female size, and males mating larger females therefore sire more offspring per mating event. Similarly, females encounter males more frequently than they need to mate. Large males produce larger spermatophores than small males and the offspring production of female increases with the size of the spermatophore she receives. Additionally, large spermatophores allow females to fertilize eggs for a longer period. Thus, mating with large males reduces the female’s need for frequent matings and she may sire sons that produce more offspring because size is heritable in copepods. Finally, we show that both males and females mate preferentially with large partners. This is the first demonstration of sexual selection by mate choice in a planktonic organism.     

Random size‐assortative mating despite size‐dependent fecundity in a Neotropical amphibian with explosive reproduction

Sexual selection theory predicts that, when body size is correlated with fecundity, there should be fitness advantages for mate choice of the largest females. Moreover, because larger males are expected to monopolise the largest females, this should result in an assortative mating based on body size. Although such patterns could be expected in both explosive and prolonged breeders, non‐assortative mating should be more widespread in species under time constraints. However, patterns of sexual selection are largely unexplored in explosive breeding species, and contrasting patterns have been found previously. We expect that the active choice of partners may be particularly risky when the time period during which sexual partners are available is severely limited. Therefore, to avoid missing an entire reproductive act, males and females should pair irrespective of traits, such as body size. We tested this hypothesis by investigating the mating patterns of the Pacific horned toad, Ceratophrys stolzmanni, a short‐lived fossorial species inhabiting Neotropical dry forests. This species is particularly adequate to test our prediction because it reproduces explosively over the course of a single night per year. Although the number of eggs laid was proportional to the size of females, and individuals of both sexes showed variation in body size, there was no assortative mating based either on size, body condition or age of mates. Egg size was not influenced by either female size or clutch size. The larger body size of females compared to males is likely due to fecundity selection, that is, the selective pressure that enhances reproductive output. Although we cannot dismiss the possibility that individuals could select their partners based on other criteria than those related to size or age, the results fit well our prediction, showing that the explosive breeding makes improbable an active choice of partners in both sexes and therefore favours a random mating pattern.     

Reproductive Success and Sexual Selection in Wild Eastern Tiger Salamanders (<Emphasis Type="Italic">Ambystoma t. tigrinum</Emphasis>)

Variation in reproductive success is most pronounced in species with strongly biased operational sex ratios, prominent sexual dimorphisms, and where mate competition and choice are likely. We studied sexual selection in eastern tiger salamanders (Ambystoma t. tigrinum) and examined the role of body size on reproductive success. We genotyped 155 adults and 1,341 larvae from 90 egg masses at six microsatellite loci. Parentage analyses revealed both sexes engaged in multiple matings, but was more common among females (64%) than males (27%). However, the standardized variance in mating and reproductive success was higher in males. Bateman gradients were significant and nearly identical in both sexes, suggesting that sexual selection was roughly equal between sexes. Body size was not correlated with mating or reproductive success in either sex. The apparent lack of sexual selection on body size may be a result of sperm storage, sperm competition, alternative mating tactics, and/or random induction of spermatophores.     

Sexual selection and speciation in mammals,butterflies and spiders

Recently refined evolutionary theories propose that sexual selection and reproductive conflict could be drivers of speciation. Male and female reproductive optima invariably differ because the potential reproductive rate of males almost always exceeds that of females: females are selected to maximize mate 'quality', while males can increase fitness through mate 'quantity'. A dynamic, sexually selected conflict therefore exists in which 'competitive' males are selected to override the preference tactics evolved by 'choosy' females. The wide variation across taxa in mating systems therefore generates variance in the outcome of intrasexual conflict and the strength of sexual selection: monandry constrains reproductive heterozygosity and allows female choice to select and maintain particular (preferred) genes; polyandry promotes reproductive heterozygosity and will more likely override female choice. Two different theories predict how sexual selection might influence speciation. Traditional ideas indicate that increased sexual selection (and hence conflict) generates a greater diversity of male reproductive strategies to be counteracted by female mate preferences, thus providing elevated potentials for speciation as more evolutionary avenues of male-female interaction are created. A less intuitively obvious theory proposes that increased sexual selection and conflict constrains speciation by reducing the opportunities for female mate choice under polyandry. We use a comparative approach to test these theories by investigating whether two general measures of sexual selection and the potential for sexual conflict have influenced speciation. Sexual size dimorphism (across 480 mammalian genera, 105 butterfly genera and 148 spider genera) and degree of polyandry (measured as relative testes size in mammals (72 genera) and mating frequency in female butterflies (54 genera)) showed no associations with the variance in speciosity. Our results therefore show that speciation occurs independently of sexual selection.     

The complexity of mating decisions in stalk‐eyed flies

All too often, studies of sexual selection focus exclusively on the responses in one sex, on single traits, typically those that are exaggerated and strongly sexually dimorphic. They ignore a range of less obvious traits and behavior, in both sexes, involved in the interactions leading to mate choice. To remedy this imbalance, we analyze a textbook example of sexual selection in the stalk‐eyed fly (Diasemopsis meigenii). We studied several traits in a novel, insightful, and efficient experimental design, examining 2,400 male–female pairs in a “round‐robin” array, where each female was tested against multiple males and vice versa. In D. meigenii, females exhibit strong mate preference for males with highly exaggerated eyespan, and so we deliberately constrained variation in male eyespan to reveal the importance of other traits. Males performing more precopulatory behavior were more likely to attempt to mate with females and be accepted by them. However, behavior was not a necessary part of courtship, as it was absent from over almost half the interactions. Males with larger reproductive organs (testes and accessory glands) did not make more mating attempts, but there was a strong tendency for females to accept mating attempts from such males. How females detect differences in male reproductive organ size remains unclear. In addition, females with larger eyespan, an indicator of size and fecundity, attracted more mating attempts from males, but this trait did not alter female acceptance. Genetic variation among males had a strong influence on male mating attempts and female acceptance, both via the traits we studied and other unmeasured attributes. These findings demonstrate the importance of assaying multiple traits in males and females, rather than focusing solely on prominent and exaggerated sexually dimorphic traits. The approach allows a more complete understanding of the complex mating decisions made by both males and females.     

Mating Group Size and Stability in Reindeer Rangifer tarandus: The Effects of Male Characteristics,Sex Ratio and Male Age Structure

In polygynous mating systems, males compete intensely for mates and may mate several females during a single reproductive season. Accordingly, factors influencing the ability of males to control a larger number of females during the breeding season can provide information on the processes underlying sexual selection. In ungulates, age, body mass and social rank are considered good predictors of the reproductive success of males, but how male age structure and sex ratio in the population influence mating group (MG) dynamics has received little empirical testing. Between 1996 and 2005, we manipulated male age‐ and sex structure and monitored MG dynamics in a reindeer (Rangifer tarandus) population. We investigated the influence of male characteristics, percentage of males and male age structure on MG size and stability. We found that males with higher social rank (that were also older and heavier) controlled larger MGs (therefore had greater mating opportunities) and had more stable MGs (corresponding to a higher ability to maintain and control females) than males of lower social rank. Moreover, MG size and MG stability decreased as the percentage of males in the population increased, most likely resulting from greater male–male competition and increased female movements. Male age structure did not influence MG stability. Given the positive relationship between mating success and MG size (and likely MG stability), frequent female movements and intense competition among males to control females seem to be the principal components of reindeer MGs dynamic.     

Sexual Competition,Coercive Mating and Mate Assessment in the One‐Sided Livebearer,Jenynsia multidentata: Are They Predictive of Sexual Dimorphism?

We investigated the mechanisms of sexual selection operating on body size in the one‐sided livebearer (Jenynsia multidentata), a small fish characterized by male dwarfism. Mating in the one‐sided livebearer is coercive: males approach females from behind and try to thrust their copulatory organ at the female genital pore. Females counter males' mating attempts by either swimming away or attacking them. We tested the hypothesis that the components of sexual selection favouring small size in males (sexual coercion) were more effective than those favouring a large size (male competition and mate choice). When alone, small males had a significantly higher success in their mating attempts than large males. The proportion of successful attempts was also positively correlated with female size. When two males competed for the same female, the large male had a significant mating advantage over the small one. With a 1 : 1 sex ratio, the large‐male mating advantage vanished because each male tended to follow a different female. Large males, however, preferentially defended large females, thus compelling small males to engage with smaller, less fecund females. Males did not discriminate between gravid and non‐gravid females, but preferred mating with larger females. This preference disappeared when males were much smaller than the female, probably in relation to the risk for the male of being eaten or injured by the female. In a choice chamber, male‐deprived females that had their sperm storage depleted remained close to males and showed a preference for large individuals, a behaviour not observed in non‐deprived females. Nonetheless, when placed with males in the same aquarium, all females showed avoidance and aggression. Struggling may represent a way by which the female assesses the skill and endurance of males.     

Cost of reproduction in male medflies: The primacy of sexual courting in extreme longevity reduction

In polygynous insect species, male reproductive success is directly related to lifetime mating success. However, the costs for males of sexual activities such as courting, signaling, and mating are largely unknown. We studied the cost of sexual activities in male Mediterranean fruit flies, Ceratitis capitata (Tephritidae), a polygynous lekking species, by keeping cohorts of individual male flies under relaxed crowding conditions in the laboratory. We used 5 cohorts among which individuals differed in their opportunities to interact with con-specifics and recorded life span, and in one treatment, mating rate. We found that males kept singly lived more than twice as long as males that interacted intensively with mature virgin females, while male-male interactions caused a smaller reduction in longevity. Because longevity of males that could court but not mate was not significantly different from those that could court and mate, we conclude that courting (not mating) was responsible for the observed longevity reduction. Moreover, we detected high variability in male mating success, when 5 virgin females were offered daily. In contrast to the cohort level, individual males that mated at a high rate lived relatively long, thus indicating heterogeneity in quality or sexual strategy among males.