Costs Of Mating Research Articles

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.

Precopulatory but not postcopulatory male reproductive traits diverge in response to mating system manipulation in Drosophila melanogaster.

Competition between males creates potential for pre‐ and postcopulatory sexual selection and conflict. Theory predicts that males facing risk of sperm competition should evolve traits to secure their reproductive success. If those traits are costly to females, the evolution of such traits may also increase conflict between the sexes. Conversely, under the absence of sperm competition, one expectation is for selection on male competitive traits to relax thereby also relaxing sexual conflict. Experimental evolution studies are a powerful tool to test this expectation. Studies in multiple insect species have yielded mixed and partially conflicting results. In this study, we evaluated male competitive traits and male effects on female costs of mating in Drosophila melanogaster after replicate lines evolved for more than 50 generations either under enforced monogamy or sustained polygamy, thus manipulating the extent of intrasexual competition between males. We found that in a setting where males competed directly with a rival male for access to a female and fertilization of her ova polygamous males had superior reproductive success compared to monogamous males. When comparing reproductive success solely in double mating standard sperm competition assays, however, we found no difference in male sperm defense competitiveness between the different selection regimes. Instead, we found monogamous males to be inferior in precopulatory competition, which indicates that in our system, enforced monogamy relaxed selection on traits important in precopulatory rather than postcopulatory competition. We discuss our findings in the context of findings from previous experimental evolution studies in Drosophila ssp. and other invertebrate species.

Male tree weta are attracted to cuticular scent cues but do not discriminate according to sex or among two closely related species

AbstractRecognition of conspecifics is an essential precursor of successful mating. Where related species coexist, species discrimination might be important, but because related species are similar, species signal recognition may actually be low. Chemical cues such as cuticular hydrocarbons (CHCs) are frequently used by insects to identify suitable sexual partners. We predicted that New Zealand tree weta (Hemideina spp.), a genus of nocturnal ensiferan Orthoptera that live both allopatrically and sympatrically, use chemical signals from either frass or CHCs to find mates. In a series of six laboratory trials using both H. thoracica and H. crassidens, we found that male tree weta, but not female tree weta, occupied cavities primed with female cuticular cues more often than cavities without. However, males did not discriminate between chemical cues of male and female conspecifics, or between conspecifics and heterospecifics. In field trials, tree weta did not occupy artificial cavities primed with either female frass or female cuticular cues more often than unscented cavities. However, in both trials weta preferentially returned to cavities that had already been occupied earlier in the trials. A final field trial confirmed the presence of mixed species harems during the mating season in one region of sympatry. Our results suggest that selection on sex and species specific chemical cues that could be used to find conspecific mates is weak. Mixed species aggregations suggest that identification of conspecific mating cues has not evolved to be species specific. We infer that for male tree weta, the cost of mating with heterospecifics is likely less than not mating at all.

Relative weighting of acoustic information during mating decisions in grasshoppers indicates signatures of sexual selection

The decision with whom to mate is crucial in determining an individual’s fitness and is often based on the evaluation of visual or acoustic displays produced during courtship. Accordingly, the algorithms for evaluating such courtship signals are shaped by sexual selection and should reflect the expected benefits and costs of mating: signals bearing heterospecific features should be rapidly rejected, since mating would produce no fertile offspring, while signals resembling conspecific ones should be weighted proportional to mate quality. We test these hypotheses in females of the grasshopper Chorthippus biguttulus who assess males by their song, which is produced as a sequence of subunits with species and individual specific signatures. We present mixed sequences of subunits with conflicting cues and use a computational model of decision-making to infer how sensory information is weighted and integrated over the song. Consistent with our hypothesis, females do weight sensory cues according to the expected fitness benefits/costs: heterospecific subunits are weighted particularly negatively and lead to a rejection of the male early in the song. Conspecific subunits are weighted moderately, permitting a more complete evaluation of the full song. However, there exists an overall negative bias against mating, possible causes of which are discussed.

Using whole-group metabolic rate and behaviour to assess the energetics of courtship in red-sided garter snakes

Reproductive effort is an important aspect of life history as reproductive success is arguably the most important component of fitness. Males tend to compete for access to females and, in the process, expend their energetic capital on mate searching, male–male competition and courtship rather than directly on offspring. Red-sided garter snakes, Thamnophis sirtalis parietalis , are an exceptional model for studying energetic costs of courtship and mating as they fast during the spring mating season, which segregates the cost of energy acquisition from the cost of courtship and mating. However, measuring an individual male's metabolic rate during courtship is complicated by the fact that male courtship behaviour in red-sided garter snakes is dependent on both the detection of a female sexual attractiveness pheromone and on facilitated courtship (i.e. vigorous courtship is only exhibited in the presence of other males). Thus, traditional techniques of placing a mask over the head of individuals would prevent male courtship behaviour, and single animals placed in a flow-through chamber would not yield ecologically realistic levels of courtship, which are only seen in the context of a mating aggregation in this species. Because of these difficulties, we placed groups of males in a flow-through metabolic chamber together with a single female whose respiratory gases were vented outside the chamber to yield a whole-group metabolic rate during competitive courtship. We also measured the standard metabolic rates (SMR) of the males individually for comparison with active metabolic rates. Conservative estimates of peak group metabolic rates during courtship are 10–20 times higher than resting group metabolic rate, which was 1.88 times higher than SMR. These measurements, coupled with the fact that these males are aphagous during the breeding, indicates that costs of courtship may be high for males and has implications for the male mating tactics in this system.

Context-dependent female mate choice maintains variation in male sexual activity.

The existence of individual variation in males' motivation to mate remains a conundrum as directional selection should favour high mating frequencies. Balancing selection resulting from (context-dependent) female mate choice could contribute to the maintenance of this behavioural polymorphism. In dichotomous choice tests, mosquitofish (Gambusia holbrooki) females preferred virtual males showing intermediate mating frequencies, reflecting females' tendencies to avoid harassment by highly sexually active males. When tested in the presence of a female shoal—which protects females from male harassment—focal females showed significantly stronger preferences for high sexual activity. A trade-off between (indirect) benefits and (direct) costs of mating with sexually active males probably explains context-dependent female mate choice, as costs depend on the social environment in which females choose their mates. No preference was observed when we tested virgin females, suggesting that the behavioural pattern described here is part of the learned behavioural repertoire of G. holbrooki females.

Relative ranges of mating and dispersal modulate Allee thresholds in sessile species

Sessile organisms, including plants and benthic macrofauna, are often restricted in the ranges over which they are able to reproduce and disperse. This leads to spatial patterning within populations, causing the effective population density around each individual to depart from the average across its range. This has important implications for population dynamics, in particular the minimum density at which populations are able to maintain positive growth (the Allee threshold). Here we compare the population dynamics of species with three syndromes — spatially restricted mating, dispersal or both — against a null model of a species with no spatial limitations. First we demonstrate mathematically that the population density at which Allee effects occur systematically shifts in each case. Next we use individual-based models representing three exemplar species to simulate the implications for the Allee threshold of each within a fixed area. In the case where mating occurs over long ranges but dispersal is restricted (e.g. the wind-pollinated silver fir, Abies alba Mill.), there is a negligible impact on the Allee threshold. When mating is also spatially restricted (e.g. the dipterocarp tree Shorea curtisii Dyer ex King), the Allee threshold reduces, unless high death rates prevent the stabilisation of aggregations. This occurs because offspring remain within the range of potential mating partners. Finally we consider a case in which mating is short-ranged, and dispersal effectively unrestricted, but in which individuals choose to locate themselves in the vicinity of conspecifics (e.g. acorn barnacles, Semibalanus balanoides). This has the effect of maintaining clustering in the face of high dispersal, reducing the Allee threshold, and compensating for the apparent cost of short-range mating. Incorporating information on ranges of mating and dispersal can lead to more effective models for the management of populations at low density, in particular the identification of species with syndromes which make them vulnerable to Allee effects. Most notably, mechanisms which increase the degree of clustering in populations increase both their resilience and persistence when finding a mate is the greatest challenge faced by a sessile organism.

FAKTOR-FAKTOR YANG MEMPENGARUHI NILAI TAMBAH USAHA TERNAK SAPI DI DESA TUMARATAS KECAMATAN LANGOWAN BARAT

ABSTRACT FACTORS INFLUENCING VALUE ADDED OF CATTLE BUSINESS AT TUMARATAS VILLAGE DISTRICT OF LANGOWAN BARAT.The objective of this research was to know value added and factors influencing value added on cattle business at Tumaratas Village district of Langowan Barat, Minahasa Regency. Primary data were collected from 100 samples of households by using questionnaire. Respondents were purposively selected by considering farmers at least has one cattle and ever sold it out. . Data were analyzed by using descriptive and quantitative analysis by using multiple regression model. Study results indicated that the more cattle owned by household the more value added of cattle achieved. The average of value added per animal unit was IDR 4,434,543/years. Partially factors of inseminator cost, cost of natural mating and household labor on cattle business had positive affect on value added of cattle while household labor on food crops business had negative impact on value added of cattle.Key words: Value added, inseminator cost, natural mating cost, household labor

Can females choose to avoid mating failure in the seed bug Lygaeus simulans?

It is becoming increasingly clear that copulation does not necessarily always lead to offspring production in many organisms, despite fertilization success presumably being under both strong natural and sexual selection. In the seed bug Lygaeus simulans, between 40% and 60% of copulations fail to produce offspring, with this ‘mating failure’ representing a significantly repeatable male-associated trait. Mating has been demonstrated to be costly in this species and, as such, we might expect females to minimize the chance of mating failure by displaying a preference for males with higher insemination success where possible. After assaying males for mating failure, we asked whether females preferred males with a history of successful inseminations versus unsuccessful inseminations in pairwise mate choice trials. Contrary to our expectations, females showed no preference for more successful over less successful males. Moreover, females showed no preference for larger males in the choice trials, even though larger males were significantly more likely to successfully inseminate females in the initial assay. This apparent lack of female precopulatory choice suggests that postcopulatory choice mechanisms may be key to mating failure in this species. However, this does not necessarily explain why females pay the cost of mating with males they will then reject via postcopulatory processes. More generally, our results suggest that mating failure may play a largely underappreciated role in mating systems evolution, influencing both the cost of choosiness, and the costs and benefits of polyandry.

Pleiotropic Effects of DDT Resistance on Male Size and Behaviour

Understanding the evolution and spread of insecticide resistance requires knowing the relative fitness of resistant organisms. In the absence of insecticides, resistance is predicted to be costly. The Drosophila melanogaster DDT resistance allele (DDT-R) is associated with a male mating cost. This could be because resistant males are generally smaller, but DDT-R may also alter courtship behaviours. Here we tested for body size and courtship effects of DDT-R on mating success in competitive and non-competitive mating trials respectively. We also assessed relative aggression in resistant and susceptible males because aggression can also influence mating success. While the effect of DDT-R on male size partly contributed to reduced mating success, resistant males also had lower rates of courtship and were less aggressive than susceptible males. These differences contribute to the observed DDT-R mating costs. Additionally, these pleiotropic effects of DDT-R are consistent with the history and spread of resistance alleles in nature.

Mating alters the link between movement activity and pattern in the red flour beetle

AbstractMating in arthropods is costly and has negative effects on survival. Such effects are often more strongly expressed when individuals are simultaneously exposed to other stress sources. Consequently, the behaviour of virgin and mated individuals often differs. Mated females, for example, search for suitable oviposition sites, whereas virgin females search more for mates. In the present study, we examine the effect of mating separately for females and males on four key behaviours of the red flour beetles: movement activity, movement along the edges of an arena, latency to emerge from shelter and preference for dark microhabitat. After mating, both sexes increase their activity at the same time as moving less along the arena edge, leading to a change in movement pattern. Females possibly change their movement pattern to locate suitable oviposition sites, whereas males perhaps do so to detect additional females with which to mate. Latency to emerge from shelter and dark preference are not influenced by mating, although they increase when measured again after 1 week. Of these behaviours, only movement activity is consistent at the individual level. We also examine whether mating incurs a cost as expressed in the time required to recover from a chill‐coma. The latter is a common proxy of cold tolerance in ectotherms. By contrast to our prediction, mating has no effect on chill‐coma recovery time, suggesting that either a single mating event does not incur sufficient stress or that there is possibly no trade‐off between the energetic cost of mating and of cold tolerance.

Evolution of male and female choice in polyandrous systems.

We study the evolution of male and female mating strategies and mate choice for female fecundity and male fertilization ability in a system where both sexes can mate with multiple partners, and where there is variation in individual quality (i.e. in the availability of resources individuals can allocate to matings, mate choice and production of gametes). We find that when the cost of mating differs between sexes, the sex with higher cost of mating is reluctant to accept matings and is often also choosy, while the other sex accepts all matings. With equal mating costs, the evolution of mating strategies depends on the strength of female sperm limitation, so that when sperm limitation is strong, males are often reluctant and choosy, whereas females tend to accept available matings. Male reluctance evolves because a male's benefit per mating diminishes rapidly as he mates too often, hence losing out in the process of sperm competition as he spends much of his resources on mating costs rather than ejaculate production. When sperm limitation is weaker, females become more reluctant and males are more eager to mate. The model thus suggests that reversed sex roles are plausible outcomes of polyandry and limited sperm production. Implications for empirical studies of mate choice are discussed.

Convergent Reversion to Single Mating in a Wasp Social Parasite.

While eusociality arose in species with single-mating females, multiple mating by queens has evolved repeatedly across the social ants, bees, and wasps. Understanding the benefits and costs of multiple mating of queens is important because polyandry results in reduced relatedness between siblings, reducing kin-selected benefits of helping while also selecting for secondary social traits that reduce intracolony conflict. The leading hypothesis for the benefits of polyandry in social insects emphasizes advantages of a genetically diverse workforce. Workerless social parasite species (inquilines) provide a unique opportunity to test this hypothesis, since they are derived from social ancestors but do not produce workers of their own. Such parasites are thus predicted to evolve single mating because they would experience the costs of multiple mating but not the benefits if such benefits accrue through the production of a genetically diverse group of workers. Here we show that the workerless social parasite Dolichovespula arctica, a derived parasite of wasps, has reverted to obligate single mating from a facultatively polyandrous ancestor, mirroring a similar reversion from obligate polyandry to approximate monandry in a social parasite of fungus-farming ants. This finding and a comparison with two other cases where inquilinism did not induce reversal to monandry support the hypothesis that facultative polyandry can be costly and may be maintained by benefits of a genetically diverse workforce.

Social dominance explains within-ejaculate variation in sperm design in a passerine bird

BackgroundComparative studies suggest that sperm competition exerts stabilizing selection towards an optimal sperm design – e.g., the relative size and covariation of different sperm sections or a quantitative measure of sperm shape - that maximizes male fertility, which results in reduced levels of within-male variation in sperm morphology. Yet, these studies also reveal substantial amounts of unexplained within-ejaculate variance, and the factors presiding to the maintenance of such within-male variation in sperm design at the population level still remain to be identified. Sperm competition models predict that males should progressively invest more resources in their germline as their mating costs increase, i.e., the soma/germline allocation trade-off hypothesis. When access to fertile females is determined by social dominance, the soma/germline allocation trade-off hypothesis predicts that dominant males should invest less in the control of spermatogenesis. Hence, dominance should positively correlate with within-male variance in sperm design.ResultsIn support of this hypothesis, we found that dominant house sparrow males produce ejaculates with higher levels of within-ejaculate variation in sperm design compared to subordinate males. However, after experimentally manipulating male social status, this pattern was not maintained.ConclusionsOur results suggest that males might control variation in sperm design according to their social status to some extent. Yet, it seems that such within-ejaculate variation in sperm design cannot be rapidly adjusted to a new status. While variation in sperm design could result from various non-exclusive sources, we discuss how strategic allocation of resources to the somatic vs. the germline functions could be an important process shaping the relationship between within-male variation in sperm design and social status.

No evidence of queen thelytoky following interspecific crosses of the honey bees Apis cerana and Apis mellifera

The human-mediated dispersal of species over geographical boundaries can bring previously isolated sister taxa into contact. Interspecific mating between closely related species may then occur, with various outcomes ranging from hybridization to reproductive interference. In the case of the Eastern honey bee Apis cerana and the Western honey bee Apis mellifera, an additional possible reproductive outcome has been posited: interspecific sperm triggers queens to produce daughters from unfertilized eggs via thelytokous parthenogenesis. Such an outcome would go unnoticed in natural population mergers, as queens, which are polyandrous, are likely to mate with both conspecific and interspecific males. We performed reciprocal crosses between A. mellifera and A. cerana via artificial insemination, plus control inseminations of saline (five queens per species per treatment), and genetically assessed the sex and origin of any resulting offspring. Neither A. cerana nor A. mellifera queens produced viable female brood after receiving interspecific semen, indicating a high cost of interspecific mating for both species. In two A. cerana colonies headed by cross-inseminated queens, workers responded by activating ovaries and laying eggs that were mainly male but occasionally female (i.e. thelytokous, 2% of brood), despite the queen’s continued presence in the nest. We conclude that thelytoky is not a consistent response to interspecific mating by queens of A. mellifera or A. cerana. Rather, at least in A. cerana, when colonies are faced with “mis-mated” queens, it may be up to the workers to secure the reproductive future of the colony.

Balanced intake of protein and carbohydrate maximizes lifetime reproductive success in the mealworm beetle, Tenebrio molitor (Coleoptera: Tenebrionidae)

Recent developments in insect gerontological and nutritional research have suggested that the dietary protein:carbohydrate (P:C) balance is a critical determinant of lifespan and reproduction in many insects. However, most studies investigating this important role of dietary P:C balance have been conducted using dipteran and orthopteran species. In this study, we used the mealworm beetles, Tenebrio molitor L. (Coleoptera: Tenebrionidae), to test the effects of dietary P:C balance on lifespan and reproduction. Regardless of their reproductive status, both male and female beetles had the shortest lifespan at the protein-biased ratio of P:C 5:1. Mean lifespan was the longest at P:C 1:1 for males and at both P:C 1:1 and 1:5 for females. Mating significantly curtailed the lifespan of both males and females, indicating the survival cost of mating. Age-specific egg laying was significantly higher at P:C 1:1 than at the two imbalanced P:C ratios (1:5 or 5:1) at any given age throughout their lives, resulting in the highest lifetime reproductive success at P:C 1:1. When given a choice, beetles actively regulated their intake of protein and carbohydrate to a slightly carbohydrate-biased ratio (P:C 1:1.54–1:1.64 for males and P:C 1:1.3–1:1.36 for females). The self-selected P:C ratio was significantly higher for females than males, reflecting a higher protein requirement for egg production. Collectively, our results add to a growing body of evidence suggesting the key role played by dietary macronutrient balance in shaping lifespan and reproduction in insects.

Female Age Determines Remating Behavior in Wild Mexican Fruit Flies

Male and female age are important factors that can influence mating and remating behavior. Females can discriminate against or prefer older males, but there have been relatively fewer studies on how female and male age influence female remating. Here we showed in wild flies of the Mexican fruit fly Anastrepha ludens (Loew), that when females were given a choice between males of different ages, younger females preferred to mate with younger males over older males, while older females were less selective. Also, when given a choice between males of different ages, older females had longer copulation durations than younger females. On the other hand, older males and females had lower mating success, compared with young and middle-aged flies under no choice conditions. However, middle-aged females mated faster compared to young females and young males mated faster compared to middle-aged males. Male age did not influence female remating, while female age strongly determined female remating, with no females remating when they were old. It is unclear if female receptivity mechanisms are switched off at older ages, or if females are reluctant to remate due to possible costs of mating. We discuss our results in terms of how male and female age can influence mating decisions.

Incomplete species recognition entails few costs in spider mites, despite first-male precedence

The consequences of heterospecific matings may hinge on interspecies interactions, but also on characteristics of the intraspecies mating system, namely sperm precedence. Indeed, first-male precedence may entail costs of heterospecific matings that are usually overlooked in other systems, such as fertilization of oocytes that become unavailable to subsequent conspecific males or a decrease in female receptivity. Here, we used a system composed of two co-occurring haplodiploid spider-mite species with first-male precedence, Tetranychus urticae and Tetranychus evansi, to investigate (a) the potential costs of heterospecific matings and (b) whether mites avoid heterospecific mates. We found that heterospecific matings did not result in fertilized offspring (i.e. females). Moreover, fecundity (i.e. male offspring) of heterospecifically mated females did not differ from that of virgins, indicating that oocyte viability was not affected by heterospecific males. Furthermore, heterospecific matings did not trigger behavioural changes that typically derive from conspecific matings, namely reduced female receptivity for subsequent matings. In avoidance tests, we found that T. evansi females and T. urticae males mated as often with conspecifics as with heterospecifics, whereas T. evansi males and T. urticae females mated assortatively more often. Also, latency to copulation in virgin and mated females did not differ between conspecific and heterospecific matings, but matings between T. urticae individuals lasted longer than heterospecific matings. Therefore, heterospecific matings result in few costs despite first-male precedence and, concomitantly, species discrimination is low. Still, this study highlights the need to account for intraspecific mating systems in tests of the reproductive consequences of mating with heterospecifics. In species where the first male fertilizes all the offspring (first-male precedence), mating with individuals from other species often yields few benefits and entails potential costs in terms of future mating events. Yet, several species exhibit incomplete recognition of conspecifics. We here show that this is the case among two spider-mite species that co-occur under natural conditions. However, we also demonstrate that the cost of mating with the ‘wrong’ species is low, even though they exhibit first-male precedence.

Direct benefits from choosing a virgin male in the European grapevine moth, Lobesia botrana

In Lepidoptera, male investment in the ejaculate usually declines over consecutive matings, a depletion that could have profound consequences for female reproductive output. Since successive matings can affect the ability of males to provide phenotypic benefits, there may be strong selection for females to discriminate between males with different mating experience. The aim of our study was to determine whether monandrous females of the European grapevine moth, Lobesia botrana , are able to discriminate between males of different quality based on their mating experience in order to maximize direct benefits (by receiving large spermatophores from virgin males) and minimize mating costs (by avoiding low-quality nonvirgin males). Nonvirgin males produced spermatophores five times smaller than those of virgin males; consequently, mating with nonvirgin males significantly reduced female fecundity and increased their motivation to remate. In a mate preference experiment, we found that females were more likely to mate with virgin males and more frequently rejected nonvirgin mates. Moreover, nonvirgin males required more time to achieve mating than virgin males. Our results suggest that females are able to discriminate between males with different mating experience, and prefer virgin males, thereby maximizing direct benefits associated with receiving large spermatophores.

Hot males live fast and die young: habitat segregation, reproductive output, and lifespan of sympatric Mnais damselflies

The Japanese damselflies Mnais costalis and Mnais pruinosa show microhabitat segregation in response to forest sunlight conditions in their sympatric habitat: M. costalis prefers sunny sites while M. pruinosa prefers semi-shady sites. We tested whether sunlight conditions at territorial sites influenced reproductive output, territory occupancy, and/or reproductive lifespan of males of the two species differently. Oviposition duration of females after copulation was used as the measure of reproductive output of individual males. We recorded illuminance at each territorial site on sunny days during the behavioral observation periods. M. costalis males at sites with higher illuminance had a higher reproductive output than other territorial males, while M. pruinosa males had a relatively lower reproductive output at such sites. During a reproductive season, we performed population censuses in a 500-m area of stream, which contained at least 112 potential territorial sites. Using a fish-eye converter, we took a hemispherical photograph to estimate canopy openness as a measure of insolation at each territorial site and examined whether males incur higher survival costs by holding territories at sunnier sites. Minimum reproductive lifespan, estimated as days between the first and the last sightings, showed that M. costalis males that occupied sunnier sites had a shorter lifespan than those occupying shadier sites, while M. pruinosa males did not show such a relationship. These results suggest that microhabitat segregation of these two Mnais damselflies reflects a species difference in the tradeoff between the benefit of mating rate and cost of survival in the sun. We report a field study on the relationships among thermal environment, temperature tolerance, reproductive success, and character displacement in the mating systems of two species of territorial Mnais damselflies. Allopatric populations of these two species are forest dwellers, and males of each species show wing color polymorphism linked to alternative mating behaviors. When these species are sympatric, males lose their polymorphisms and change their habitat preferences: M. pruinosa prefers shady parts of a stream, while M. costalis prefers sunnier parts. We showed the costs and benefits of character displacement coupled to microhabitat preference shift. The findings of this study may highlight an underappreciated area of study, namely, the interplay between behavioral and physiological ecology in insects.