Competition For Mates Research Articles

Mutation of the seminal protease gene, serine protease 2, results in male sterility in diverse lepidopterans

Sterile insect technology (SIT) is an environmentally friendly method for pest control. As part of our efforts to develop a strategy that results in engineered male-sterile strains with minimum effects on viability and mating competition, we used CRISPR/Cas9 technology to disrupt Ser2, which encodes a seminal fluid protein, in the model lepidopteran insect, Bombyx mori, and an important agricultural pest, Plutella xylostella. Disruption of Ser2 resulted in dominant heritable male sterility. Wild-type females mated with Ser2-deficient males laid eggs normally, but the eggs did not hatch. We detected no differences in other reproductive behaviors in the mutant males. These results support the conclusion that Ser2 gene is necessary for male reproductive success in diverse lepidopterans. Targeting Ser2 gene has the potential to form the basis for a new strategy for pest control.

Using Sexual Selection Theories to Examine Contextual Variation in Heterosexual Women\u2019s Orientation Toward High Heels

High heels are symbols of female sexuality and are “costly signals” if the risks of wearing them are offset by improving women’s attractiveness to men. From a functionalist perspective, the costs versus benefits of wearing heels may vary according to personal and contextual factors, such as her effectiveness at competing for mates, or at times when such motives are stronger. Here, we examined potential differences between women (self-rated attractiveness, dyadic versus solitary sexual desire, women’s age, competitive attitudes toward other women) and contextual variation (priming mating and competitive motives) in their responses to high heels. Study 1 (N = 79) and Study 2 (N = 273) revealed that self-rated attractiveness was positively related to orientation toward heeled shoes. When examining responses to two very attractive shoes (one higher heel, one lower heel) in Study 2, dyadic sexual desire, but not solitary sexual desire or intrasexual competitiveness, predicted their inclination to buy the higher-heeled shoe. In Study 3 (N = 142), young women chose high heels when primed with free choice of a designer shoe (95% CI [53.02 mm, 67.37 mm]) and preferred a heel 22 mm (0.87”) higher than older women (Study 4, N = 247). Contrary to predictions, priming mating or competitive motives did not alter women’s preference toward a higher heel (Studies 3 and 4). Our studies suggest that attractive women augment their physical appeal via heels. High heels may be a subtle indicator of dyadic sexual desire, and preferences for heels are stronger at times in the lifespan when mating competition is relatively intense.

Kin but less than kind: within-group male relatedness does not increase female fitness in seed beetles.

Theory maintains within-group male relatedness can mediate sexual conflict by reducing male–male competition and collateral harm to females. We tested whether male relatedness can lessen female harm in the seed beetle Callosobruchus maculatus. Male relatedness did not influence female lifetime reproductive success or individual fitness across two different ecologically relevant scenarios of mating competition. However, male relatedness marginally improved female survival. Because male relatedness improved female survival in late life when C. maculatus females are no longer producing offspring, our results do not provide support for the role of within-group male relatedness in mediating sexual conflict. The fact that male relatedness improves the post-reproductive part of the female life cycle strongly suggests that the effect is non-adaptive. We discuss adaptive and non-adaptive mechanisms that could result in reduced female harm in this and previous studies, and suggest that cognitive error is a likely explanation.

Understanding resource driven female-female competition: ovary and liver size in sand gobies.

The operational sex ratio (OSR, ready-to-mate males to females) is a key factor determining mating competition. A shortage of a resource essential for reproduction of one sex can affect OSR and lead to competition within the opposite sex for resource-holding mates. In the sand goby (Pomatoschistus minutus), a fish with paternal care, male readiness to mate depends on acquiring a nest-site, whereas food abundance primarily impacts female egg production. Comparing body condition and gonadal investment of fish from two populations with different availability in resources (Baltic Sea: few nest-sites, more food; North Sea: many nest-sites, less food), we predicted females carrying more mature eggs in the Baltic Sea than in the North Sea. As predicted, ovaries were larger in Baltic Sea females, and so was the liver (storage of energy reserves and vitellogenic compounds) for both sexes, but particularly for females. More females were judged (based on roundness scores) to be ready to spawn in the Baltic Sea. Together with a nest colonization experiment confirming a previously documented difference between the two areas in nest-site availability, these results indicate a more female-biased OSR in the Baltic Sea population, compared to the North Sea, and generates a prediction that female–female competition for mating opportunities is stronger in the Baltic population. To our knowledge, this is the first time that female reproductive investment is discussed in relation to OSR using field data.

Experimental evidence that winning or losing a fight does not affect sperm quality in a field cricket

AbstractFighting is a powerful social experience that can affect male reproductive behavior, including ejaculatory strategies. Whereas winners may monopolize females, losers may instead perceive high sperm competition and limited future mating opportunities, and accordingly enhance ejaculate quality to maximize their reproductive success. In male field crickets Gryllus bimaculatus that fight aggressively for control of breeding territories, winners are known to possess sperm of lower quality (viability) compared to losers, but it remains unclear whether this is due to short‐term fighting consequences. To test if the fighting experience per se (winning or losing) affects male adjustment of sperm viability, we subjected males to winning and losing experiences by staging fights against size‐matched rivals of known fighting ability. These rivals were males that previously won or lost a fight and, due to “winner‐loser effects” kept winning or losing subsequent contests. We sampled sperm prior and after the fight and twice in control males with no fighting experience and found no differences in sperm viability across measures. We conclude that males do not tailor their ejaculate quality following a single fight, or based on its outcome. Intrinsic differences in other attributes between winners and loser phenotypes may explain differences in sperm quality previously described in this system.

Allyl‐2,6‐dimethoxyphenol, a female‐biased compound, is robustly attractive to conspecific males of Bactrocera dorsalis at close range

AbstractInsect cuticular hydrocarbons (CHCs) play important roles in mate recognition and chemical communication. To explore the cues regulating courtship and mating behaviour in the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), CHCs were extracted from mature virgin female and male oriental fruit flies using n‐hexane. Nine compounds – i.e., 4‐allyl‐2,6‐dimethoxyphenol (designated ‘compound 3’) and eight ester compounds – had significantly greater abundance in female samples than in males. Of these nine compounds, six (1, 2, 4, 5, 6, and 8) elicited electrophysiological responses from the antennae of male flies. Compound 3 did not elicit a detectable male antennal response, but in Y‐tube olfactometer bioassays, it exhibited robust attractiveness to conspecific males at close range. We speculate that compound 3 is a close‐range sex pheromone in B. dorsalis. A mating competition experiment revealed that compound 3 significantly increased the competitiveness of males, which implied that compound 3 might be used in control programs of B. dorsalis.

Sex roles and the evolution of parental care specialization.

Males and females are defined by the relative size of their gametes (anisogamy), but secondary sexual dimorphism in fertilization, parental investment and mating competition is widespread and often remarkably stable over evolutionary timescales. Recent theory has clarified the causal connections between anisogamy and the most prevalent differences between the sexes, but deviations from these patterns remain poorly understood. Here, we study how sex differences in parental investment and mating competition coevolve with parental care specialization. Parental investment often consists of two or more distinct activities (e.g. provisioning and defence) and parents may care more efficiently by specializing in a subset of these activities. Our model predicts that efficient care specialization broadens the conditions under which biparental investment can evolve in lineages that historically had uniparental care. Major transitions in sex roles (e.g. from female-biased care with strong male mating competition to male-biased care with strong female competition) can arise following ecologically induced changes in the costs or benefits of different care types, or in the sex ratio at maturation. Our model provides a clear evolutionary mechanism for sex-role transitions, but also predicts that such transitions should be rare. It consequently contributes towards explaining widespread phylogenetic inertia in parenting and mating systems.

Cyberbullying, cyber aggression, and cyber victimization in relation to adolescents' dating and sexual behavior: An evolutionary perspective.

This study examined adolescents' cyberbullying, cyber aggression, and cyber victimization from an evolutionary perspective, extending previous research showing that traditional forms of bullying, aggression, and victimization are associated with reproductively relevant outcomes. Consistent with hypotheses based on theory and research linking bullying and aggression to intrasexual competition for mates, results indicated that cyber victimization was positively associated with a number of dating and sexual partners. Findings for cyber aggression were more complex, depending on the degree of cyber victimization experienced by the perpetrator, and the balance of power between the perpetrator and victim. Specifically, nonbullying cyber aggression by perpetrators with equal or less power than the victim had stronger positive relations with the number of dating or sexual partners when perpetrators experienced a high level of cyber victimhood. In contrast, cyberbullying by perpetrators with more power than the victim was negatively associated with the number of dating partners when the perpetrators' exposure to cyber victimization was low. Although cyber aggression and cyber victimization are new forms of aggression that involve the use of modern electronic devices, the results of this study demonstrate the usefulness of viewing this behavior from an evolutionary perspective and show that adolescents are likely to use cyber aggression against rivals in the context of intrasexual competition for mates.

Does Sex Imbalance Affect Family Businesses? Evidence from Rural China

This paper suggests that sex imbalance is a gender-related determinant of entrepreneurship. China has been experiencing an increasing surplus of men in the pre-marital age cohort since the late 1970s. This sex imbalance intensifies the mating competition among single men, thus stimulating households with sons to build wealth through start-up businesses. By examining households’ ownership of businesses based on a 2009 Rural Finance Survey in China, we find that son households are more likely to own businesses in villages where the sex imbalance is more severe. We further provide evidence that these son households are more capable of sustaining their businesses.

Early Sibling Conflict May Ultimately Benefit the Family.

Relatives often interact differently with each other than with nonrelatives, and whether kin cooperate or compete has important consequences for the evolution of mating systems, seed size, dispersal, and competition. Previous research found that the larger of the size dimorphic seeds produced by the annual plant Aegilops triuncialis suppressed germination of their smaller sibs by 25%-60%. Here, we found evidence for kin recognition and sibling rivalry later in life among Aegilops seedlings that places seed-seed interactions in a broader context. In experiments with size dimorphic seeds, seedlings reduced the growth of sibling seedlings by ∼40% but that of nonsibling seedlings by ∼25%. These sequential antagonistic interactions between seeds and then seedlings provide insight into conflict and cooperation among kin. Kin-based conflict among seeds may maintain dormancy for some seeds until the coast is clear of more competitive siblings. If so, biotically induced seed dormancy may be a unique form of cooperation, which increases the inclusive fitness of maternal plants and offspring by minimizing competition among kin.

EFFECT OF GAMMA IRRADIATION ON THE QUALITY AND MATING COMPETITIVENES OF FRUIT FLIES Bactrocera dorsalis IN THE CAGE SCALE

Bactrocera dorsalis is an important fruit fly attack fruits and vegetables in Indonesia. Sterile Insect Technique (SIT) is sterilize with gamma irradiation, released as many as 9 x wild population, ecpected to mate but didn’t produce offspring. The research porpuse was to determine the effect of gamma irradiation on the quality and on the mating competitiveness in cage scale. The experimental design was completely randomized design with one factor was gamma irradiation dosee at 6 levels were 0 (control), 30, 50, 70, 90 and 110 Gy as many as 4 replicates. The result that the level of the radiation dose had a significant on the competitiveness and quality included the percentage of pupae became adult adult, sex ratio, the percentage of fly ability, the number of eggs produced (fecundity) and percentage hatching eggs. The quality decreased when increasing in radiation dose. The dose level didn’t affect the fecundity but affected the mating competitiveness in cage scale. The value total of mating campetitivenes was highest at a dose of 70 Gy treatment were 0.76 (5:1:1) and 0.79 (10:1:1), followed by dose of 50 Gy were 0,41 (5:1:1) and 0,50 (10:1:1).

Who determines the timing of inflorescence closure of a sexual dandelion? Pollen donors versus recipients

Male–male competition for mating or fertilization opportunities may in theory select for male manipulative adaptation that can harm males’ mates, leading to sexual conflict. Evolutionary theory predicts that selection will favor the manipulation by pollen of the duration of its recipients’ receptivity. However, there is insufficient evidence to show that pollen can exert effects on the duration of receptivity, a prerequisite for the evolution of pollen manipulative adaptation. Using a sexual diploid dandelion, Taraxacum japonicum, we conducted hand pollination experiments within and between populations to examine the effects of pollen on the timing of inflorescence (flower head) closure. We also examined the potential fitness consequences to the pollen recipients by field observation of seed production in populations with different inflorescence closure timing. Within-population experiments showed that pollination induced inflorescence closure even when some of the florets in the inflorescence were not yet pollinated with compatible pollen. Furthermore, between-population crosses revealed that pollen donors, recipients, and their interaction all influenced the timing of inflorescence closure. Different populations differed in the timing of inflorescence closure, which could affect the availability to the recipients of pollen for fertilization and thereby seed production. However, there were no significant differences in the rates of natural seed production in these populations. Our results demonstrate that pollen donors, as well as recipients, contribute to the duration of floral receptivity. We discuss the implications of our findings to the evolutionary theory of plant reproduction.

Choosy Gulf pipefish males ignore age but prefer active females with deeply keeled bodies

Within Syngnathidae (pipefish, seadragons and seahorses), male pregnancy often results in choosy males and competitive females. Females in these species often evolve secondary sexual traits and engage in courtship displays that make their ornaments more noticeable to males. Most syngnathids probably continue to grow larger throughout their lives, but we know little about the relationship between age and mating competition in these taxa. Here, we use the Gulf pipefish, Syngnathus scovelli, to investigate the roles of ornament size, courtship activity level, age and fecundity in female mating competition. We conducted male choice trials that allowed males to choose between similarly sized females of different ages. We also measured age and size at maturity. We found that females with larger ornaments were deeper bodied and engaged in longer courtship displays, yet males chose females based on body depth and display rather than ornamentation. This result suggests that ornamentation serves to help males assess female quality. Female age plays no role in male choice or in female ornamentation. Our finding that males care more about female phenotype than female age considerably simplifies the interpretation of mating patterns in natural populations of Gulf pipefish, which are characterized by considerable age structure.

May the (selective) force be with you: Spatial sorting and natural selection exert opposing forces on limb length in an invasive amphibian.

Spatial sorting on invasion fronts drives the evolution of dispersive phenotypes, and in doing so can push phenotypes in the opposite direction to natural selection. The invasion of cane toads (Rhinella marina) through tropical Australia has accelerated over recent decades because of the accumulation of dispersal-enhancing traits at the invasion front, driven by spatial sorting. One such trait is the length of the forelimbs: invasion-front toads have longer arms (relative to body length) in comparison with populations 10-20years after invasion. Such a shift likely has fitness consequences: an increase of forearm length would decrease the strength with which a male could cling to a female during amplexus and so render such a male less competitive in competition for mates, compared to short-armed conspecifics. Our laboratory trials of attachment strength confirmed that males with relatively longer arms were easier to displace, and competition trials show higher duration of amplexus for males with shorter arms. Together with the sharp cline in limb length observed behind the invasion front, these results imply an opposition of selective forces: spatial sorting optimizes dispersal, but as this force wanes behind the invasion front, we see the primacy of natural selection reassert itself.

Comparison between pupal and adult X-ray radiation, designed for the sterile insect technique for Aedes albopictus control

Aedes albopictus is a vector of several human viral diseases, including dengue, chikungunya, and Zika. New control method for Aedes albopictus is needed to replace traditional methods such as chemical insecticides which induce resistance, environmental contamination and toxicity to human. In sterile insect technique (SIT), male mosquitoes are sterilized by γ-ray or X-ray irradiation before released. In this study, the relative effectiveness of X-ray irradiation as a mosquito SIT was investigated. Both pupal and adult Aedes albopictus were subjected to different radiation doses and their emergence, survivorship, longevity, induced sterility, and male mating competitiveness were evaluated. Relative to controls, irradiation had no significant effect on emergence and survivorship but significantly reduce adult longevity. Induced sterility were essentially same for both irradiated pupal and adult. At a dose of 40 Gy, 97% and 100% sterility was respectively achieved for males and females. Mating competitiveness was reduced both in adult males and those derived from pupae exposed to 40 Gy. However, populations can be suppressed by increasing the release ratio (sterile: normal). When the release ratio was 7:1, 74% of the wild population could be suppressed. Overall, the results of the present study showed that SIT based on X-Ray irradiation is scientific and feasible to control Aedes albopictus.

Parthenogenetic Females of the Stick Insect Clitarchus hookeri Maintain Sexual Traits.

The New Zealand stick insect Clitarchus hookeri has both sexual and parthenogenetic (all-female) populations. Sexual populations exhibit a scramble competition mating system with distinctive sex roles, where females are signalers and males are searchers, which may lead to differences in the chemical and morphological traits between sexes. Evidence from a range of insect species has shown a decay of sexual traits is common in parthenogenetic lineages, especially those traits related to mate attraction and location, presumably due to their high cost. However, in some cases, sexual traits remain functional, either due to the recent evolution of the parthenogenetic lineage, low cost of maintenance, or because there might be an advantage in maintaining them. We measured morphological and chemical traits of C. hookeri to identify differences between males and females and between females from sexual and parthenogenetic populations. We also tested the ability of males to discriminate between sexual and parthenogenetic females in a laboratory bioassay. Our results show that male C. hookeri has morphological traits that facilitate mobility (smaller body with disproportionately longer legs) and mate detection (disproportionately longer antennae), and adult females release significantly higher amounts of volatile organic compounds than males when this species is sexually active, in accordance with their distinctive sex roles. Although some differences were detected between sexual and parthenogenetic females, the latter appear to maintain copulatory behaviors and chemical signaling. Males were unable to distinguish between sexual and parthenogenetic females, suggesting that there has been little decay in the sexual traits in the parthenogenetic lineage of C. hookeri.

Competitively mediated changes in male toad calls can depend on call structure

Abstract Males of many species aggregate in large groups where they signal to attract females. These large aggregations create intense competition for mates, and the simultaneous signaling by many individuals can impair any given male’s ability to attract females. In response to this situation, male signals can be modified, either evolutionarily or facultatively, such that the detectability of the signal is enhanced. The way in which signals are modified varies among even closely related species, yet few studies have evaluated what causes such variation. Here, we address this issue using male spadefoot toads (Spea multiplicata and Spea bombifrons), which call to attract females. Using data from natural populations, we examined if, and how, male calls of 3 different call types (S. multiplicata with a slow call, S. bombifrons with a slow call, and S. bombifrons with a fast call) varied depending on competition with other males. We found that in both call types consisting of slow calls, call pulse rate decreased with increasing competition. By contrast, in the call type consisting of fast calls, call rate decreased with increasing competition. Moreover, we found that the relationship between competition and male call effort—a measure of the energy that males expend in calling––differed between the call types. Such variation in male signals in response to competition can have important implications for explaining diversity in male signals and patterns of sexual selection.

Seasonal and diurnal patterns of population vocal activity in avian brood parasites

Patterns of vocal activity may involve information about vocalizations themselves as well as their function. In birds, vocal activity at the individual and population level is generally closely associated with breeding cycles, reaching the peak during territorial and mating competition, and decreasing with the onset of egg incubation and chick feeding. However, little is known about patterns of vocal activity in avian brood parasites that have unusual breeding cycles without parental care. Using passive acoustic monitoring, we determined the seasonal and diurnal patterns of population vocal activity in two avian brood parasites: the Common CuckooCuculus canorusand the Lesser CuckooC. poliocephalus. We found that both species and both sexes showed a similarly highly structured pattern of seasonal vocal activity, reaching a sharp peak in the early breeding season when birds compete for territories and mates, although males sang more frequently than females. Likewise, the diurnal patterns of vocal activity were similar in both species and both sexes of cuckoos, with peak activity occurring around dawn. Nocturnal calls by male cuckoos were also detected in both species, but only in the early breeding season. Collectively, the observed patterns of population vocal activity may suggest that the absence of parental care may not extend the period of vocal activity in these two species of brood parasites.

Male competition and the evolution of mating and life-history traits in experimental populations of Aedes aegypti.

Aedes aegypti is an important disease vector and a major target of reproductive control efforts. We manipulated the opportunity for sexual selection in populations of Ae. aegypti by controlling the number of males competing for a single female. Populations exposed to higher levels of male competition rapidly evolved higher male competitive mating success relative to populations evolved in the absence of competition, with an evolutionary response visible after only five generations. We also detected correlated evolution in other important mating and life-history traits, such as acoustic signalling, fecundity and body size. Our results indicate that there is ample segregating variation for determinants of male mating competitiveness in wild populations and that increased male mating success trades-off with other important life-history traits. The mating conditions imposed on laboratory-reared mosquitoes are likely a significant determinant of male mating success in populations destined for release.

Allometry and morphological trait relationship in the sexually dimorphic Chinese dobsonfly, Acanthacorydalisasiatica (Wood-Mason, 1884) (Megaloptera, Corydalidae).

Male insects with large weapons such as horns and elongate mandibles would be expected to invest more on such structures than other parts of the body for advantages in male to male competition for mating. In male genitalia, however, intermediate size provides a better fit for more females than small or large sizes, and such a male would leave more offspring regardless of their body size. These predictions were tested using a static allometry analysis between body size and other trait sizes. Acanthacorydalisasiatica is a large dobsonfly (Megalotera) and males have conspicuously large mandibles used as weapons. We examined the hypothesis that the male mandibles of this sexually dimorphic species are sexually selected to enlarge, whereas the male genitalia are stable to be intermediate regardless of a great variation in body size. The results, as predicted, showed positive allometry between male body size and mandible length but negative allometry between male body size and ectoproct length (a male grasping structure). Sperm are transferred through a small spermatophore attached externally to the female genital opening, so it may be evolutionarily unnecessary to develop an enlarged male genital size. In contrast, there may be a trade-off between male mandible size and wing length, because of negative allometry between body size and wing length in males but isometry between them in females.