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.     

Is bigger better? Male body size affects wing‐borne courtship signals and mating success in the olive fruit fly,Bactrocera oleae (Diptera: Tephritidae)

Variations in male body size are known to affect inter‐ and intrasexual selection outcomes in a wide range of animals. In mating systems involving sexual signaling before mating, body size often acts as a key factor affecting signal strength and mate choice. We evaluated the effect of male size on courtship displays and mating success of the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae). Wing vibrations performed during successful and unsuccessful courtships by large and small males were recorded by high‐speed videos and analyzed through frame‐by‐frame analysis. Mating success of large and small males was investigated. The effect of male–male competition on mating success was evaluated. Male body size affected both male courtship signals and mating outcomes. Successful males showed wing‐borne signals with high frequencies and short interpulse intervals. Wing vibrations displayed by successful large males during copulation attempt had higher frequencies over smaller males and unsuccessful large males. In no‐competition conditions, large males achieved higher mating success with respect to smaller ones. Allowing large and small males to compete for a female, large males achieve more mating success over smaller ones. Mate choice by females may be based on selection of the larger males, able to produce high‐frequency wing vibrations. Such traits may be indicative of “good genes,” which under sexual selection could means good social‐interaction genes, or a good competitive manipulator of conspecifics.     

Sexual conflict over mating in Gnatocerus cornutus? Females prefer lovers not fighters

Female mate choice and male–male competition are the typical mechanisms of sexual selection. However, these two mechanisms do not always favour the same males. Furthermore, it has recently become clear that female choice can sometimes benefit males that reduce female fitness. So whether male–male competition and female choice favour the same or different males, and whether or not females benefit from mate choice, remain open questions. In the horned beetle, Gnatocerus cornutus, males have enlarged mandibles used to fight rivals, and larger mandibles provide a mating advantage when there is direct male–male competition for mates. However, it is not clear whether females prefer these highly competitive males. Here, we show that female choice targets male courtship rather than mandible size, and these two characters are not phenotypically or genetically correlated. Mating with attractive, highly courting males provided indirect benefits to females but only via the heritability of male attractiveness. However, mating with attractive males avoids the indirect costs to daughters that are generated by mating with competitive males. Our results suggest that male–male competition may constrain female mate choice, possibly reducing female fitness and generating sexual conflict over mating.     

Sexual Strategies of a North American ‘Tarantula’ (Araneae: Theraphosidae)

Despite their general notoriety and popularity as pets, little is known of the behavioural ecology of ‘tarantulas’ or theraphosid spiders. We studied a theraphosid of the Arizona deserts, Aphonopelma sp., to determine behavioural events crucial to successful courtship and mating. Males search for spatially scattered females and, at short range, may detect females by substrate-borne cues. When two males are present with a single female, no direct competition such as aggression is observed. Both males may mate with a single female in rapid succession, with no evidence of post-copulatory mate guarding. Despite the potential for sexual cannibalism, courtship and mating behaviour patterns exhibit few aggressive elements and males nearly always survive sexual encounters with females. The mating system of this Aphonopelma species may best be described as a type of scramble-competition polygyny, in which the ability of males to locate receptive females is an important determinant of mating success in males. Multiple mating by females renders predictions concerning fertilization success uncertain, due to the possibility of sperm competition and ‘cryptic’ female mate choice.     

Sexual Selection in the Water Spider: Female Choice and Male–Male Competition

The water spider Argyroneta aquatica is the only spider spending its whole life under water, and one of the few spider species in which males are larger than females. Previous studies indicated that males can cannibalize females, which is uncommon among spiders. Here we aimed to further test for a potential influence of sexual selection on male body size. We examined the importance of female choice by testing whether females prefer the larger of two simultaneously presented males as mating partners. Further, we examined the influence of male–male competition by comparing the fighting behaviour between large and small males when alone or when together with a female, and we determined the outcome of fights. We found that females approach and choose large males as mating partners, despite the risk of male cannibalism. Additionally, males intensively compete for females, and large males clearly win against smaller ones. Hence sexual selection seems to be important for the evolution of the peculiar sexual size dimorphism of water spiders, as large size is beneficial for males in both the intra‐ and intersexual context. Previous studies have suggested an important role of natural selection in the sex‐specific body size of water spiders, but natural and sexual selection mechanisms apparently work in the same direction, favouring large male size.     

Male Courtship Behavior and Weapon Trait as Indicators of Indirect Benefit in the Bean Bug,Riptortus pedestris

Females prefer male traits that are associated with direct and/or indirect benefits to themselves. Male–male competition also drives evolution of male traits that represent competitive ability. Because female choice and male–male competition rarely act independently, exploring how these two mechanisms interact is necessary for integrative understanding of the evolution of sexually selected traits. Here, we focused on direct and indirect benefits to females from male attractiveness, courtship, and weapon characters in the armed bug Riptortus pedestris. The males use their hind legs to fight other males over territory and perform courtship displays for successful copulation. Females of R. pedestris receive no direct benefit from mating with attractive males. On the other hand, we found that male attractiveness, courtship rate, and weapon size were significantly heritable and that male attractiveness had positive genetic covariances with both courtship rate and weapon traits. Thus, females obtain indirect benefits from mating with attractive males by producing sons with high courtship success rates and high competitive ability. Moreover, it is evident that courtship rate and hind leg length act as evaluative cues of female choice. Therefore, female mate choice and male–male competition may facilitate each other in R. pedestris. This is consistent with current basic concepts of sexual selection.     

Female Choice, Female Reluctance to Mate and Sexual Selection on Body Size in the Dung Fly Sepsis cynipsea

We investigated the mechanisms of sexual selection in the common dung fly Sepsis cynipsea and how these affect selection on body size at the population level. Because of the presumed costs associated with mating, we predicted that there would be a decrease in the general reluctance of females to mate with any particular male at higher male densities at the mating site, a fresh cow pat, resulting in indirect female choice and a decrease in the strength of sexual selection. In contrast, classical direct female choice and male‐male competition should result in increased selection intensities because more opportunities for choice and competition exist at higher densities. Female reluctance to mate and female assessment of males are expressed in prominent female behaviour to repel mates in several insect species, including S. cynipsea. Laboratory pair‐wise choice experiments showed that large males were more likely to obtain copulations, which also ensued more promptly, suggesting female assessment of male quality (direct female choice). There was a basic influence of male activity but little further effect of male scramble competition on the outcome of mating. Another laboratory experiment showed a decrease in female shaking duration per male, associated with an asymptote in the shaking duration per female, as male density and harassment increased, but did not show the increase in mating frequency predicted by the female reluctance hypothesis. A study estimating sexual selection differentials in the field showed that directional selection for larger males was present overall and was negatively related to seasonally mediated variation in male density. Our study suggests that direct female choice in combination with indirect female choice (due to an interaction of female reluctance to mate and male persistence) is most consistent with the behavioural and selection patterns observed in S. cynipsea, but male effects cannot be definitively excluded.     

Is size assortative mating in Paracalliope fluviatilis (Crustacea: Amphipoda) explained by male–male competition or female choice?

Field and laboratory studies were used to assess: (1) whether size assortative mating occurred in the New Zealand amphipod Paracalliope fluviatilis and (2) hypotheses developed to explain size assortative mating. We found that assortative mating occurred and that larger females carried more eggs, suggesting they may be more valuable as mates. Laboratory experiments were then used to determine whether: (1) male size influenced the size of the female selected (mechanical constraints hypothesis); (2) male size influenced pairing success in the presence of competition (intrasexual selection hypothesis); (3) take‐overs of females occurred and whether large males were more successful (intrasexual selection hypothesis); (4) guard duration varied relative to male and female size (guard duration hypothesis); and (5) females had control over pairing success and guard duration (intersexual selection hypothesis). Although there was evidence to suggest the existence of intrasexual competition for mates (i.e. both small and large males preferred large females), there was no evidence of overt competition (i.e. takeovers of paired females). There was also no difference with respect to how long small and large males guarded females, but large females were guarded longer by both male size classes. Females handicapped by having their mobility reduced were guarded for the same duration as control females but males were more likely to pair with handicapped females, suggesting that they were easier to amplex. Given the lack of evidence for direct male–male competition or female choice, we suggest that assortative mating may be the result of: (1) indirect competition (e.g. in situ large males may be better able to access and amplex the largest females) or (2) female resistance to small males in combination with higher costs that small males may incur in securing large females. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 173–181.     

Beauty and the beast: mechanisms of sexual selection in humans

Literature in evolutionary psychology suggests that mate choice has been the primary mechanism of sexual selection in humans, but this conclusion conforms neither to theoretical predictions nor available evidence. Contests override other mechanisms of sexual selection; that is, when individuals can exclude their competitors by force or threat of force, mate choice, sperm competition, and other mechanisms are impossible. Mates are easier to monopolize in two dimensional mating environments, such as land, than in three-dimensional environments, such as air, water, and trees. Thus, two-dimensional mating environments may tend to favor the evolution of contests. The two-dimensionality of the human mating environment, along with phylogeny, the spatial and temporal clustering of mates and competitors, and anatomical considerations, predict that contest competition should have been the primary mechanism of sexual selection in men. A functional analysis supports this prediction. Men's traits are better designed for contest competition than for other sexual selection mechanisms; size, muscularity, strength, aggression, and the manufacture and use of weapons probably helped ancestral males win contests directly, and deep voices and facial hair signal dominance more effectively than they increase attractiveness. However, male monopolization of females was imperfect, and female mate choice, sperm competition, and sexual coercion also likely shaped men's traits. In contrast, male mate choice was probably central in women's mating competition because ancestral females could not constrain the choices of larger and more aggressive males through force, and attractive women could obtain greater male investment. Neotenous female features and body fat deposition on the breasts and hips appear to have been shaped by male mate choice.     

Female Choice or Male Sex Drive? The Advantages of Male Body Size during Mating in Drosophila Melanogaster

The mating success of larger male Drosophila melanogaster in the laboratory and the wild has been traditionally been explained by female choice, even though the reasons are generally hard to reconcile. Female choice can explain this success by virtue of females taking less time to mate with preferred males, but so can the more aggressive or persistent courtships efforts of large males. Since mating is a negotiation between the two sexes, the behaviors of both are likely to interact and influence mating outcomes. Using a series of assays, we explored these negotiations by testing for the relative influence of male behaviors and its effect on influencing female courtship arousal threshold, which is the time taken for females to accept copulation. Our results show that large males indeed have higher copulation success compared to smaller males. Competition between two males or an increasing number of males had no influence on female sexual arousal threshold;—females therefore may have a relatively fixed ‘arousal threshold’ that must be reached before they are ready to mate, and larger males appear to be able to manipulate this threshold sooner. On the other hand, the females’ physiological and behavioral state drastically influences mating; once females have crossed the courtship arousal threshold they take less time to mate and mate indiscriminately with large and small males. Mating quicker with larger males may be misconstrued to be due to female choice; our results suggest that the mating advantage of larger males may be more a result of heightened male activity and relatively less of female choice. Body size per se may not be a trait under selection by female choice, but size likely amplifies male activity and signal outputs in courtship, allowing them to influence female arousal threshold faster.     

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.     

A novel method of comparing mating success and survival reveals similar sexual and viability selection for mobility traits in female tree crickets

The relationship between sexual and viability selection in females is necessarily different than that in males, as investment in sexual traits potentially comes at the expense of both fecundity and survival. Accordingly, females do not usually invest in sexually selected traits. However, direct benefits obtained from mating, such as nuptial gifts, may encourage competition among females and subsidize investment into sexually selected traits. We compared sexual and viability selection on female tree crickets Oecanthus nigricornis, a species where females mate frequently to obtain nuptial gifts and sexual selection on females is likely. If male choice determines female mating success in this species, we expect sexual selection for fecundity traits, as males of many species prefer more fecund females. Alternatively, intrasexual scramble or combat competition on females may select for larger jumping legs or wider heads (respectively). We estimated mating success in wild caught crickets using microsatellite analysis of stored sperm and estimated relative viability by comparing surviving female O. nigricornis to those captured by a common wasp predator. In support of the scramble competition hypothesis, we found sexual selection for females with larger hind legs and narrower heads. We also found stabilizing viability selection for intermediate head width and hind leg size. As predicted, traits under viability and sexual selection were very similar, and the direction of that selection was not opposing. However, because the shape of sexual and viability selection differs, these episodes of selection may favour slightly different trait sizes.     

Fitness effects of female mate choice: preferred males are detrimental for Drosophila melanogaster females

The evolution of female mate choice, broadly defined to include any female behaviour or morphology which biases matings towards certain male phenotypes, is traditionally thought to result from direct or indirect benefits which females acquire when mating with preferred males. In contrast, new models have shown that female mate choice can be generated by sexual conflict, where preferred males may cause a fitness depression in females. Several studies have shown that female Drosophila melanogaster bias matings towards large males. Here, we use male size as a proxy for male attractiveness and test how female fitness is affected by reproducing with large or small males, under two different male densities. Females housed with large males had reduced lifespan and aged at an accelerated rate compared with females housed with small males, and increased male density depressed female fitness further. These fitness differences were due to effects on several different fitness components. Female fitness covaried negatively with male courtship rate, which suggests a cost of courtship. Mating rate increased with male size, whereas female fitness peaked at an intermediate mating rate. Our results suggest that female mate choice in D. melanogaster is, at least in part, a by-product of sexual conflict over the mating rate.     

Evolutionary causes of male-biased sexual size dimorphism from a female perspective in the seed bug Togo hemipterus (Heteroptera: Lygaeidae)

Sexual size dimorphisms (SSDs) in body size are expected to evolve when selection on female and male sizes favors different optima. Many insects show female-biased SSD that is usually explained by the strong fecundity advantage of larger females. However, in some insects, males are as large as or even larger than females. The seed bug Togo hemipterus (Scott) also exhibits a male-biased SSD in body size. Many studies that have clarified the evolutionary causes of male-biased SSD have focused only on male advantages due to male–male competition. To clarify the evolutionary causes of male-biased SSD in body size, we should examine the degree of not only the sexual selection that favors larger males but also natural selection that is acting on female fecundity. The obtained results, which showed higher mating acceptance rates to larger males, implies that females prefer larger males. No significant relationship was detected between female body size and fecundity; body size effects on female fecundity were weak or undetectable. We conclude that male-biased SSD in T. hemipterus can be accounted for by a combination of sexual selection through male–male competition and female choice favoring large males, plus weak or undetectable natural selection that favors large females due to a fecundity advantage.     

SEXUAL SELECTION AND MALE CHARACTERISTICS IN THE BLUEHEAD WRASSE,THALASSOMA BIFASCIATUM: MATING SITE ACQUISITION,MATING SITE DEFENSE,AND FEMALE CHOICE

Through a series of replacement experiments with the bluehead wrasse, Thalassoma bifasciatum, we have identified male morphological characteristics that appear to be under phenotypic sexual selection. We were particularly interested in whether the various sources of sexual selection (male-male competition for unoccupied mating sites, defense of mating sites against small males, and female choice of males) were (1) independently associated with different phenotypic characteristics; (2) jointly affected the same characteristic in the same way; or (3) jointly affected the same characteristic in an antagonistic fashion. We replaced the resident large, brightly colored Terminal Phase (TP) males on a reef with the same number of TP males from other reefs. When transplanted, these males contest with each other to take over mating sites. The transplanted group of males were then scored for three components of fitness: (1) the quality of the site obtained through competition with other large males; (2) the male's ability to defend arriving females from small intruding males; and (3) changes in female visits to the site once the new male takes over. The first and second components are part of intrasexual selection; the third represents intersexual selection. We measured the opportunity for selection by partitioning variance in mating success, and measured the direct effects of sexual selection by estimating the covariance between morphology and fitness components. Opportunities for selection: Because females generally remain faithful to particular mating sites, most (54%) of the explainable variation in male mating success is due to the acquisition of a particular mating territory, which is the outcome of competition among TP males. There was less variation in mating success due to shifts in site use by females and defense of females against the intrusions of smaller males, but all components were significant. Effects of selection: Success in male–male competition among TP males, estimated by the quality of the territory acquired, was positively associated with body length and the relative length of the pectoral fin. Success in territorial defense against small males was primarily related to body length, with lesser contributions from body depth and the area of a white band on the flank. Contribution to fitness through female choice of males was positively associated with white band area. In the two instances where a character was associated with two fitness components, the direction of selection was the same. While body length was positively associated with winning intrasexual contests, it was not correlated to any behavioral measures of aggression. Similarly, the white band associated with attractiveness was not correlated with any aspect of courtship or aggression. Parasite load was uncorrelated with other morphological characters, and did not appear to affect any aspect of sexual selection. There was no evidence for stabilizing selection or significant additional contributions from second-order effects to the fitness surfaces. Fitness functions calculated using cubic splines were generally linear except for body length, which appeared sigmoid in its effect on site acquisition ability; this same feature tended to plateau in its effect on site defense. Analyses of the interactions of selection gradients with reef or experiment indicated that the effect of particular male characters on estimates of fitness was generally homogeneous in both time and space.     

Sexual Selection in Black Morph Girardinus metallicus (Pisces: Poeciliidae): Females Can Spot a Winner (But We Cannot)

Male–male competition may interfere with the ability of females to choose mates by interrupting courtship or by favoring highly aggressive males who may damage females during mating attempts. Alternatively, females may benefit by mating with dominant males, and female choice and male–male competition may therefore act in unison. The same traits, including aggressiveness, may indicate male quality to females and to rivals. We investigated sexual selection in the black morph of the endemic Cuban poeciliid fish, Girardinus metallicus, to ascertain the links between morphological and behavioral traits and success in intra‐ and intersexual selection. Males conspicuously exhibit their black ventral surface and gonopodium to females during courtship. Dichotomous choice tests revealed female association preferences for certain males, and those same males were more successful in monopolizing access to females when the fish were allowed to directly interact. Dominant males followed, courted, and copulated with females more than subordinate males within a pair, and it appears that females could either assess dominance based on cues we did not measure, or could influence subsequent mating success by their behavior during the dichotomous choice trials. There was an interaction between black status (i.e., whether the male in each pair had more or less ventral black coloration than the other male in that pair) and dominance, such that low‐black dominant males courted early and then shifted to following females, whereas high‐black dominant males courted far more later in the observation period. These results hint at the importance for sexual selection of the interplay between a static morphological trait (black coloration) and a dynamic behavioral trait (aggressiveness), but the functional significance of the courtship display remains a mystery.     

Size‐Dependent Male Mate Preference and its Association with Size‐Assortative Mating in a Mangrove Snail,Littoraria ardouiniana

In many animals, body size plays a crucial role in mating success in the context of competition and preference for mates. Increasing evidence has shown that male mate preference can be size‐dependent and, therefore, an important driver of size‐assortative mating. To test this theory, mate choice experiments were performed during the three consecutive stages of mating behaviour, namely trail following, shell mounting and copulation, in the dioecious mangrove snail, Littoraria ardouiniana. These experiments identified two possible forms of size‐dependent male mate preference which could contribute to the formation of size‐assortative mating in these snails. Firstly, whereas small males were unselective, large males were selective and preferred to follow mucus trails laid by large females. Alternatively, the results can also be interpreted as all males were selective and adopted a mating strategy of selecting females similar to, or larger than, their own sizes. Both small and large males also copulated for longer with large than with small females, and this was more pronounced in large males. When two males encountered a female, they engaged in physical aggression, with the larger male excluding the smaller male from copulating with the female. This study, therefore, demonstrated that size‐dependent male mate preference may, along with male–male competition, play an important role in driving size‐assortative mating in these mangrove snails, and this may also be the case in other species that exhibit male mate choice.     

Male Sexual Signals and Female Choice in Drosophila grimshawi (Diptera: Drosophilidae)

Sexual selection and sexual signaling have been prominent topics in recent behavioral studies, but limited data have led to controversy regarding these topics. For example, the Hawaiian Drosophila are often cited as examples in which female choice has resulted in the evolution of elaborate male courtship signals, but relatively few data exist to test these claims adequately. We studied D. grimshawi, a lek-forming Hawaiian Drosophila, to determine whether there was evidence for female choice without male competition and to elucidate the possible cues females use to discriminate. Male mating success was found to be nonrandom and males that courted females intensely and deposited many pheromone-containing streaks on the substrate were the most successful. Hence, multiple cues seem to be involved in male mating success in this species. Some males performed only one display, however, and may represent an alternate male mating tactic. The protein content of the adult male diet significantly influenced the level of pheromone streak deposition, and thus, foraging environment may affect the outcome of sexual selection.     

Sperm competition generates evolution of increased paternal investment in a sex role‐reversed seed beetle

When males provide females with resources at mating, they can become the limiting sex in reproduction, in extreme cases leading to the reversal of typical courtship roles. The evolution of male provisioning is thought to be driven by male reproductive competition and selection for female fecundity enhancement. We used experimental evolution under male‐ or female‐biased sex ratios and limited or unlimited food regimes to investigate the relative roles of these routes to male provisioning in a sex role‐reversed beetle, Megabruchidius tonkineus, where males provide females with nutritious ejaculates. Males evolving under male‐biased sex ratios transferred larger ejaculates than did males from female‐biased populations, demonstrating a sizeable role for reproductive competition in the evolution of male provisioning. Although larger ejaculates elevated female lifetime offspring production, we found little evidence of selection for larger ejaculates via fecundity enhancement: males evolving under resource‐limited and unlimited conditions did not differ in mean ejaculate size. Resource limitation did, however, affect the evolution of conditional ejaculate allocation. Our results suggest that the resource provisioning that underpins sex role reversal in this system is the result of male–male reproductive competition rather than of direct selection for males to enhance female fecundity.     

INTRASEXUAL COMPETITION ALONE FAVORS A SEXUALLY DIMORPHIC ORNAMENT IN THE RUBYSPOT DAMSELFLY HETAERINA AMERICANA

I studied the sex-limited red spots on the wings of male rubyspot damselflies (Hetaerina americana) in relation to territoriality and fitness in the wild. Both observational and experimental (wing spot manipulation) studies indicated that wing spots were selected through competition among males for mating territories, not through female choice or direct competition for females. Males with naturally or artificially large wing spots were more successful at holding territories and consequently mated at higher rates than males with relatively small wing spots. In contrast, sexual selection on male body size appeared to operate among nonterritorial males at the clasping stage of the mating sequence, perhaps because larger males were better at clasping females forcibly. Of four models proposed to explain the evolution of ornaments through territory competition, only the agonistic handicap model makes predictions consistent with the results of this study.