Competition For Mates Research Articles

Phoresy

White et al. introduce the phenomenon of phoresy - animals hitching a ride on other animals.

Patterns of intraspecific aggression inferred from injuries in an aquatic turtle with male-biased size dimorphism

Patterns of sexual size dimorphism (SSD) in turtles are correlated with ecological mode, and it has been hypothesized that mating systems are also shaped by ecological mode. Male combat and coercive mating are competing explanations for male-biased SSD, but are difficult to assess empirically in aquatic species with cryptic behaviour. We quantified SSD and compiled observations of putative combat wounds collected from over 500 captures of Snapping Turtles (Chelydra serpentina (L., 1758)) in Algonquin Provincial Park, Ontario, to test hypotheses of mate competition and coercion. We found that both sex and body size were important predictors of risk of wounding, consistent with the hypothesis that male–male sexual competition is the primary driver of intraspecific aggression. Low wounding rates among females suggests that resource competition and coercive mating are not important causes of injuries. The risk of wounding increased monotonically with body size in adult males but not in adult females, and small males were less likely to be injured, suggesting that they employ a risk-averse strategy by avoiding direct competition for mates. There was no evidence of asymptotic or decreasing wounding probability in the largest males, which is consistent with the hypothesis that large males compete most intensively to monopolize mates.

Multicontinental community phylogenetics of avian mixed‐species flocks reveal the role of the stability of associations and of kleptoparasitism

If understood as a way to forage socially without incurring intra‐specific competition for mates or other resources, mixed‐species foraging flocks are predicted to be composed of functionally similar species. In the most intensively studied mixed‐species foraging system, understory forest birds, relevant functional traits are however extremely difficult to measure and best replaced by phylogenetic relatedness. A multicontinental analysis of flock phylogenetic structure revealed departures from the expected phylogenetic clustering. Long‐lasting associations (> one day) were phylogenetically overdispersed, indicating that these associations are affected by competitive exclusion or by mutualistic interactions. However, where kleptoparasites occurred, this effect disappeared completely, as expected if the dilution of kleptoparasitism risk compensated competition between related species. Mixed‐species flocks should not be analyzed as a homogeneous phenomenon.

Visibility and Persistence of Marker Dyes and Effect on the Quality and Mating Competitiveness of Mass-Reared Flies (Diptera: Tephritidae): Anastrepha obliqua and Bisexual and Genetic Sexing (Tapachula-7) Strains of A. ludens.

Fluorescent dyes are commonly used in the sterile insect technique (SIT) for marking insects for a proper identification after recapture. However, the quality of the mark must be balanced against insect performance, because dyes can negatively affect some parameters of insect performance and reduce their effectiveness in control with the SIT. We determined the visibility and persistence and the effect of dyes on the quality of Anastrepha obliqua (Macquart) and Anastrepha ludens (Loew) (bisexual and genetic sexing strains) by testing four concentrations of a dye (Day-Glo) from 0 to 2.5 g dye/kg of pupae. Visibility and persistence of the mark were positively affected by dose and negatively affected by the length of time the samples were kept in a solution of 75% alcohol. However, upon dissection, even the lowest dose of dye was visible under a fluorescence microscope. Between dyed and undyed pupae (control), no significant differences were observed in rates of emergence, fliers and flight ability, and survival in two tests, with water and without food and without water and food, at any of the concentrations tested. Furthermore, no significant difference in mating competitiveness was detected between control pupae and those dyed at 1.0 and 2.5 g dye/kg pupae. We discuss our results with the possibility of reducing the dose of dye in these three flies, because the heads are large enough to capture sufficient particles to permit identification with the current methods of detection.

Body dissatisfaction and disordered eating in androphilic and gynephilic men and women

According to the theory of intra-sexual competition for mates, androphilic individuals (i.e., sexually interested in men) are expected to emphasize their physical appearance, and be less satisfied with their bodies, compared to gynephilic individuals (i.e., sexually interested in women). To test this theory against the objectification theory and the minority stress theory of body dissatisfaction and disordered eating, we measured body dissatisfaction, disordered eating, and body mass index (BMI) in both androphilic and gynephilic men and women in a large population-based sample (N=8007). Compared to gynephilic men, androphilic men were more likely to be dissatisfied with their bodies and display disordered eating. Gynephilic women were more dissatisfied with their bodies compared to androphilic women. Women were, on average, more likely to be dissatisfied with their bodies and display disordered eating compared to men. Theoretical implications of the findings were discussed.

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.

Do Male Cook Strait Giant Weta Prudently Allocate Sperm?

Sperm production is costly and so males are expected to prudently allocate sperm to matings in a manner that maximizes their fitness. Sperm competition hypotheses predict that when facing increased sperm competition risk males should increase their investment in ejaculates. In contrast, when facing high future mating opportunities, males are expected to decrease their sperm investment in the current mating. This is because males should keep in reserve an amount of sperm proportional to their expected future mating opportunities. We experimentally tested whether male Cook Strait giant weta (Anostostomatidae: Orthoptera: Deinacrida rugosa) phenotypically adjust their investment in ejaculates in relation to their perceived risk of sperm competition and future mating opportunities. D. rugosa is a large flightless orthopteran insect in which males pass multiple spermatophores to females during a day-long mating bout. Contrary to expectation, we found that low female availability (i.e. increased sperm competition risk) had no effect on male resource allocation to sperm (i.e. number of spermatophores) compared to controls whereas, contrary to expectation, males experiencing high female availability increased their ejaculate investment by transferring significantly more spermatophores to their mates. Our results might be a consequence of males being insensitive to increased presence of rival males, reducing their allocation to sperm under increasingly risky circumstances, or due to females prolonging copulations when their perceived future mating opportunities are low.

Polygamy slows down population divergence in shorebirds.

Sexual selection may act as a promotor of speciation since divergent mate choice and competition for mates can rapidly lead to reproductive isolation. Alternatively, sexual selection may also retard speciation since polygamous individuals can access additional mates by increased breeding dispersal. High breeding dispersal should hence increase gene flow and reduce diversification in polygamous species. Here, we test how polygamy predicts diversification in shorebirds using genetic differentiation and subspecies richness as proxies for population divergence. Examining microsatellite data from 79 populations in 10 plover species (Genus: Charadrius) we found that polygamous species display significantly less genetic structure and weaker isolation‐by‐distance effects than monogamous species. Consistent with this result, a comparative analysis including 136 shorebird species showed significantly fewer subspecies for polygamous than for monogamous species. By contrast, migratory behavior neither predicted genetic differentiation nor subspecies richness. Taken together, our results suggest that dispersal associated with polygamy may facilitate gene flow and limit population divergence. Therefore, intense sexual selection, as occurs in polygamous species, may act as a brake rather than an engine of speciation in shorebirds. We discuss alternative explanations for these results and call for further studies to understand the relationships between sexual selection, dispersal, and diversification.

Sex in murky waters: algal-induced turbidity increases sexual selection in pipefish

Algal-induced turbidity has been shown to alter several important aspects of reproduction and sexual selection. However, while turbidity has been shown to negatively affect reproduction and sexually selected traits in some species, it may instead enhance reproductive success in others, implying that the impact of eutrophication is far more complex than originally believed. In this study, we aimed to provide more insight into these inconsistent findings. We used molecular tools to investigate the impact of algal turbidity on reproductive success and sexual selection on males in controlled laboratory experiments, allowing mate choice, mating competition, and mate encounter rates to affect reproduction. As study species, we used the broad-nosed pipefish, Syngnathus typhle, a species practicing male pregnancy and where we have previously shown that male mate choice is impaired by turbidity. Here, turbidity instead enhanced sexual selection on male size and mating success as well as reproductive success. Effects from mating competition and mate encounter rates may thus override effects from mate choice based on visual cues, producing an overall stronger sexual selection in turbid waters. Hence, seemingly inconsistent effects of turbidity on sexual selection may depend on which mechanisms of sexual selection that have been under study.Significance statementAlgal blooms are becoming increasingly more common due to eutrophication of freshwater and marine environments. The high density of algae lowers water transparency and reduces the possibility for fish and other aquatic animals to perform behaviors dependent on vision. We have previously shown that pipefish are unable to select the best partner in mate choice trials when water transparency was reduced. However, fish might use other senses than vision to compensate for the reduction in water transparency. In this study, we found that when fish were allowed to freely interact, thereby allowing competition between partners and direct contact between the fish, the best partner was indeed chosen. Hence, the negative effects of reduced water visibility due to algal blooms may be counteracted by the use of other senses in fish.

The role of city income inequality, sex ratio and youth mortality rates in the effect of violent victimization on health-risk behaviors in Brazilian adolescents

This study integrates insights from evolutionary psychology and social epidemiology to present a novel approach to contextual effects on health-risk behaviors (unprotected sex, drunkenness episodes, drugs and tobacco experimentation) among adolescents. Using data from the 2012 Brazilian National Survey of Adolescent Health (PeNSE), we first analyzed the effects of self-reported violent victimization on health-risk behaviors of 47,371 adolescents aged 10–19 nested in the 26 Brazilian state capitals and the Federal District. We then explored whether the magnitude of these associations was correlated with cues of environmental harshness and unpredictability (youth external mortality and income inequality) and mating competition (sex ratio) from the city level. Results indicated that self-reported violent victimization is associated with an increased chance of engagement in health-risk behaviors in all Brazilian state capitals, for both males and females, but the magnitude of these associations varies in relation to broader environmental factors, such as the cities' age-specific mortality rates, and specifically for females, income inequality and sex ratio. In addition to introducing a novel theoretical and empirical approach to contextual effects on adolescent health-risk behaviors, our findings reinforce the need to consider synergies between people's life experiences and the conditions where they live, when studying health-risk behaviors in adolescence.

Own attractiveness and perceived relationship quality shape sensitivity in women’s memory for other men on the attractiveness dimension

Although recent work suggests that opposite-sex facial attractiveness is less salient in memory when individuals are in a committed romantic relationship, romantic relationship quality can vary over time. In light of this, we tested whether activating concerns about romantic relationship quality strengthens memory for attractive faces. Partnered women were exposed briefly to faces manipulated in shape cues to attractiveness before either being asked to think about a moment of emotional closeness or distance in their current relationship. We measured sensitivity in memory for faces as the extent to which they recognized correct versions of studied faces over versions of the same person altered to look either more or less-attractive than their original (i.e., studied) version. Contrary to predictions, high relationship quality strengthened hit rate for faces regardless of the sex or attractiveness of the face. In general, women’s memories were more sensitive to attractiveness in women, but were biased toward attractiveness in male faces, both when responding to unfamiliar faces and versions of familiar faces that were more attractive than the original male identity from the learning phase. However, findings varied according to self-rated attractiveness and a psychometric measure of the quality of their current relationship. Attractive women were more sensitive to attractiveness in men, while their less-attractive peers had a stronger bias to remember women as more-attractive and men as less-attractive than their original image respectively. Women in better-quality romantic relationships had stronger positive biases toward, and false memories for, attractive men. Our findings suggest a sophisticated pattern of sensitivity and bias in women’s memory for facial cues to quality that varies systematically according to factors that may alter the costs of female mating competition (‘market demand’) and relationship maintenance.

Sexual selection and sex ratios in Anolis lizards

Biased sex ratios, or unequal numbers of males and females in a population, can alter the intensity of sexual selection by enhancing competition for mates, and thus may affect the evolution of reproductive strategies. Studies of sex ratio variation across a clade provide an opportunity to examine the morphological or behavioral consequences of different levels of sexual selection. We examined sex ratio variation, using phylogenetic comparative methods, across a diverse clade of terrestrial vertebrates, the Anolis lizards. Across a sample of 14 species in 21 localities, we found remarkable bidirectional variation in sex ratios across the Anolis clade: males are more common in some populations and females in others. However, we find no evidence that sex ratio bias is associated with sexual size dimorphism, a proxy for sexual selection. Nor do we find an association of sex ratio bias with ecological niches (i.e. ecomorphs), which vary in sexual selection pressures and mating systems. The observed inter-specific variation in sex ratio suggests that a balance of different, possibly opposing, factors, including sex-specific dispersal and mortality rates, may play a role in determining population sex ratio.

Artificial selection on mating competitiveness of Anastrepha ludens for sterile insect technique application

AbstractThe sterile insect technique (SIT) has been applied successfully for the control of several fruit fly species of economic importance. In species with lek mating systems, as in the Mexican fruit fly, Anastrepha ludens (Loew) (Diptera: Tephritidae) – where the variance in male mating success is high, males have to compete with other males, and where wild females are highly selective – the success of SIT depends on the sexual competitiveness of mass‐reared sterile males. However, mass‐rearing conditions result in selection of sexual behavioral traits that differ from wild flies, reducing mating competitiveness of sterile flies and SIT efficiency. Artificial selection in mass‐rearing colonies, based on male mating success, represents an alternative to improve the sexual performance of sterile males. Here, we evaluated the effect of selection of A. ludens mass‐reared males based on their mating competitiveness. Two modes of selection were compared, one single selection event on parental flies, and continuous selection along four consecutive generations. For the offspring of each treatment in each generation, we evaluated male mating success, its association with post‐copulatory behavior through female remating inhibition, and life‐history traits that are key for mass‐rearing, such as immature survival and reproduction. Field cage mating tests revealed that wild males were more competitive than mass‐reared males (selected and unselected). Although no significant differences were found between mass‐reared selected and non‐selected males, in the fourth generation males from the selected colonies performed better than males from the non‐selected colonies and their mating competitiveness was similar to that of wild males. No consistent differences were observed in mating latency, copulation duration, or ability to inhibit female remating. Survival and fecundity decreased with increasing rearing generations, except in the colony with continuous selection where fecundity and fertility increased.

Sexual selection constrains the body mass of male but not female mice.

Sexual size dimorphism results when female and male body size is influenced differently by natural and sexual selection. Typically, in polygynous species larger male body size is thought to be favored in competition for mates and constraints on maximal body size are due to countervailing natural selection on either sex; however, it has been postulated that sexual selection itself may result in stabilizing selection at an optimal mass. Here we test this hypothesis by retrospectively assessing the influence of body mass, one metric of body size, on the fitness of 113 wild‐derived house mice (Mus musculus) residing within ten replicate semi‐natural enclosures from previous studies conducted by our laboratory. Enclosures possess similar levels of sexual selection, but relaxed natural selection, relative to natural systems. Heavier females produced more offspring, while males of intermediate mass had the highest fitness. Female results suggest that some aspect of natural selection, absent from enclosures, acts to decrease their body mass, while the upper and lower boundaries of male mass are constrained by sexual selection.

Experimental evidence for sexual selection against inbred males.

The detrimental effects of matings between relatives are well known. However, few studies determine the extent to which inbreeding depression in males is due to natural or sexual selection. Importantly, measuring fitness or key fitness components, rather than phenotypic traits allows more accurate estimation of inbreeding depression. We investigate how differences in inbreeding and juvenile diet (i.e. early stressful environment) influence a key component of male fitness, namely their reproductive success. We experimentally created inbred and outbred male mosquitofish (Gambusia holbrooki) by mating full-sibs (f=0·25). We show that this led to a 23% reduction in genome-wide heterozygosity based on SNPs. Males were raised on different diets early in life to create high-stress and low-stress rearing environments. We then allowed adult males to compete freely for females to test if inbreeding, early diet and their interaction affect a male's share of paternity. Early diet had no effect on paternity, but outbred males sired almost twice as many offspring as inbred males (n=628 offspring from 122 potential sires). Using artificial insemination methods we determined that this was unlikely to be due to early embryo mortality of eggs fertilised by inbred males: there was no evidence that male inbreeding status affects the realised fecundity of females (n=288). Given there was no difference in male mortality in our competitive mating experiment, the lower reproductive success of inbred males can most parsimoniously be attributed to inbreeding negatively affecting sexually selected traits that affect male mating success and/or sperm competitiveness. We discuss which sexually selected traits might be involved.

From Environment to Mating Competition and Super-K in a Predominantly Urban Sample of Young Adults.

Recent research suggests human life history strategy (LHS) may be subsumed by multiple dimensions, including mating competition and Super-K, rather than one. In this study, we test whether a two-dimensional structure best fit data from a predominantly urban sample of young adults ages 18–24. We also test whether latent life history dimensions are associated with environmental harshness and unpredictability as predicted by life history theory. Results provide evidence that a two-dimensional model best fit the data. Furthermore, a moderate inverse residual correlation between mating competition and Super-K was found, consistent with a life history trade-off. Our findings suggest that parental socioeconomic status may enhance investment in mating competition, that harshness might persist into young adulthood as an important correlate of LHS, and that unpredictability may not have significant effects in young adulthood. These findings further support the contention that human LHS is multidimensional and environmental effects on LHS are more complex than previously suggested. The model presented provides a parsimonious explanation of an array of human behaviors and traits and can be used to inform public health initiatives, particularly with respect to the potential impact of environmental interventions.

On the Psychometric Study of Human Life History Strategies.

This article attends to recent discussions of validity in psychometric research on human life history strategy (LHS), provides a constructive critique of the extant literature, and describes strategies for improving construct validity. To place the psychometric study of human LHS on more solid ground, our review indicates that researchers should (a) use approaches to psychometric modeling that are consistent with their philosophies of measurement, (b) confirm the dimensionality of life history indicators, and (c) establish measurement invariance for at least a subset of indicators. Because we see confirming the dimensionality of life history indicators as the next step toward placing the psychometrics of human LHS on more solid ground, we use nationally representative data and structural equation modeling to test the structure of middle adult life history indicators. We found statistically independent mating competition and Super-K dimensions and the effects of parental harshness and childhood unpredictability on Super-K were consistent with past research. However, childhood socioeconomic status had a moderate positive effect on mating competition and no effect on Super-K, while unpredictability did not predict mating competition. We conclude that human LHS is more complex than previously suggested-there does not seem to be a single dimension of human LHS among Western adults and the effects of environmental components seem to vary between mating competition and Super-K.

Sexual size dimorphism of group-living Mongolian gerbils Meriones unguicutalus (Muridae: Gerbillinae)

Polygynous mammals often have male-biased sexual size dimorphism due to male–male competition for mates. However, fecundity selection may enlarge female body size. The Mongolian gerbil Meriones unguiculatus (Milne-Edwards, 1867) is a social rodent of promiscuous mating. Male gerbils exhibit social dominance hierarchy, which may differentiate reproductive success among male gerbils with larger males having more reproductive opportunities. This study investigated the hypothesis that social dominance hierarchy would result in male-biased sexual size dimorphism in Mongolian gerbils. We also tested the prediction of fecundity selection, that litter size would be positively related to female body mass of Mongolian gerbils. Body mass, carcass weight and body length of male gerbils were greater than those of females. Therefore, male-biased sexual size dimorphism was supported in Mongolian gerbils. Although litter size of female gerbils increased with increasing carcass weight, ecological constraints (e.g. burrow living and increased energy expenditure during pregnancy) probably kept female body size smaller than male body size of the gerbil. Social interactions may mediate sexual and fecundity selections on the body size of social rodents.

Aedes aegypti Control Through Modernized, Integrated Vector Management.

Introduction: In the context of the ongoing, unprecedented Zika virus outbreak in the Americas, the World Health Organization has expressed its support for developing and up-scaling three novel approaches to controlling the Aedes aegypti mosquito: the Sterile Insect Technique (SIT), the Release of Insects carrying Dominant Lethal genes (RIDL) and the release of Wolbachia-infected mosquitoes. Whereas the former two approaches are temporary insect population suppression strategies, Wolbachia infection is a self-sustaining, invasive strategy that uses inherited endosymbiotic bacteria to render natural mosquito populations arbovirus resistant.Methods: A mathematical model is parameterised with new, Brazilian field data informing the mating competitiveness of mass-reared, released insects; and simulations compare and contrast projections of vector control achieved with the alternative approaches.Results: Important disadvantages of Wolbachia and SIT are identified: both strategies result in mosquitoes ovipositing non-viable eggs and, by alleviating intense larval competition, can cause an overall increase in survival to the adult stage. However, it is demonstrated that strategically combining the suppression methods with Wolbachia can generate a sustained control while mitigating the risks of inadvertent exacerbation of the wild mosquito population.Discussion: This initial analysis demonstrates potential for good synergy when combining novel mosquito approaches in a modernized, integrated vector control programme.

The Psychometrics of the Mini-K.

Many published studies have employed the Mini-K to measure a single fast-slow life history dimension. However, the internal structure of the Mini-K has not been determined and it is not clear that a single higher order K-factor fits the data. It is also not clear that the Mini-K is measurement invariant across groups such as the sexes. To establish the construct validity of K as well as the broader usefulness of applying life history theory to humans, it is crucial that these psychometric issues are addressed as a part of measure validation efforts. Here we report on three studies that used latent variable modeling and data drawn from two college student samples ( ns = 361 and 300) to elucidate the psychometrics of the Mini-K. We found that (a) the Mini-K had a six dimensional first-order structure, (b) the K-factor provided a parsimonious explanation of the associations among the lower order factors at no significant cost to fit, (c) the Mini-K measured the same K-factor across the sexes, (d) K-factor means did not have the same meaning across the sexes and thus the first-order factors should be used in studies of mean sex differences, and finally, (e) the K-factor was only associated with environment and aspects of mating competition in females. Implications and future directions for life history research are discussed.