Result Of Sexual Selection Research Articles

An anthropological perspective on hand grip strength as a marker of health, disease and fitness

Handgrip strength is a quick way to assess overall muscle strength. Low handgrip strength is an indicator of poor health. While handgrip strength is related with mortality and morbidity, for some parameters, handgrip strength is even a stronger predictor of health than chronological age alone. Handgrip strength is highly sexually dimorphic and has a high heritability. It is thought that this is an outcome of sexual selection and intrasexual competition in our evolutionary history. Some anthropological studies confirm this view, and it is claimed that there are relationships between grip strength and aggression, athletic performance and attractiveness, especially in men. The aim of this study is to review the relationship of diseases with handgrip strength in anthropological perspective and examine the idea that handgrip strength being a marker of biological fitness.

On a remarkable sexual dimorphic trait on scales and fins of the old world Cyprinodontiformes (Actinopterygii: Aphaniidae)

AbstractSecondary sexual dimorphism is an interesting and stupendous subject of research study due to the fact that it is a result of sexual selection, mostly attributed to either female mate choice or male–male competition. This study aims to investigate the microscopic characterization of scales and fin rays in several aphaniids (Cyprinodontiformes: Aphaniidae) to find out the possibility of using these structures as secondary sexual dimorphism traits and discuss their taxonomic and evolutionary significance. Herein, the results reveal that (i) male individuals of aphaniid species of the genera Aphanius, Aphaniops and Paraphanius present contact organs in the forms of ctenus‐like structure (in posterior margin of the scales) and spicule‐like structure (in anal fin rays) that show sexual dimorphism of scales and fins; (ii) number, position, size and shape of contact organs provide taxonomic signal to distinguish members of the genus Aphaniops from two other genera; (iii) females of Aphaniops ginaonis also represent contact organs in scales but fewer than males and (iv) as the sexual dimorphism results from different sexual selection pressures acting on males and females, it provides evolutionary signals.

Signal detection shapes ornament allometry in functionally convergent Caribbean Anolis and Southeast Asian Draco lizards.

Visual ornaments have long been assumed to evolve hyper-allometry as an outcome of sexual selection. Yet growing evidence suggests many sexually selected morphologies can exhibit other scaling patterns with body size, including hypo-allometry. The large conspicuous throat fan, or dewlap, of arboreal Caribbean Anolis lizards was one ornament previously thought to conform to the classical expectation of hyper-allometry. We re-evaluated this classic example alongside a second arboreal group of lizards that has also independently evolved a functionally equivalent dewlap, the Southeast Asian Draco lizards. Across multiple closely related species in both genera, the Anolis and Draco dewlaps were either isometric or had hypo-allometric scaling patterns. In the case of the Anolis dewlap, variation in dewlap allometry was predicted by the distance of conspecifics and the light environment in which the dewlap was typically viewed. Signal efficacy, therefore, appears to have driven the evolution of hypo-allometry in what was originally thought to be a sexually selected ornament with hyper-allometry. Our findings suggest that other elaborate morphological structures used in social communication might similarly exhibit isometric or hypo-allometric scaling patterns because of environmental constraints on signal detection.

A comprehensive overview of the effects of urbanisation on sexual selection and sexual traits.

ABSTRACTUrbanisation can affect mating opportunities and thereby alter inter‐ and intra‐sexual selection pressures on sexual traits. Biotic and abiotic urban conditions can influence an individual's success in pre‐ and post‐copulatory mating, for example through impacts on mate attraction and mate preference, fertilisation success, resource competition or rival interactions. Divergent sexual selection pressures can lead to differences in behavioural, physiological, morphological or life‐history traits between urban and non‐urban populations, ultimately driving adaptation and speciation. Most studies on urban sexual selection and mating interactions report differences between urban and non‐urban populations or correlations between sexual traits and factors associated with increased urbanisation, such as pollution, food availability and risk of predation and parasitism. Here we review the literature on sexual selection and sexual traits in relation to urbanisation or urban‐associated conditions. We provide an extensive list of abiotic and biotic factors that can influence processes involved in mating interactions, such as signal production and transmission, mate choice and mating opportunities. We discuss all relevant data through the lens of two, non‐mutually exclusive theories on sexual selection, namely indicator and sensory models. Where possible, we indicate whether these models provide the same or different predictions regarding urban‐adapted sexual signals and describe different experimental designs that can be useful for the different models as well as to investigate the drivers of sexual selection. We argue that we lack a good understanding of: (i) the factors driving urban sexual selection; (ii) whether reported changes in traits result in adaptive benefits; and (iii) whether these changes reflect a short‐term ecological, or long‐term evolutionary response. We highlight that urbanisation provides a unique opportunity to study the process and outcomes of sexual selection, but that this requires a highly integrative approach combining experimental and observational work.

Sexual selection of conspicuous consumption

Recently, a number of papers draw upon ideas from sexual selection and costly signaling theory to argue that conspicuous consumption has evolved as a sexually selected mating strategy. I outline what are considered to be the criteria for arguing that a trait is the outcome of sexual selection and I explore whether conspicuous consumption is sexual adaptation. Though I share the insight that evolutionary theory can contribute to our understanding of consumption behavior, I argue that existing evolutionary explanations of conspicuous consumption do not examine human evolved psychology and available evidence about past environments. I further argue that cultural evolution theory provides an alternative explanation of conspicuous consumption in modern environments. In particular, conspicuous consumption is understood as a pattern of behavior marked by specific social learning mechanisms. Such an approach reflects the analytical tools of cultural evolution theory and provides a classification of cognitive factors involved in consumption choices.

Sexually selected traits as bioindicators: exposure to mercury affects carotenoid-based male bill color in zebra finches.

To examine whether sexually selected traits are particularly sensitive bioindicators of environmental toxicants, we assessed the effects of exposure to environmentally relevant dietary concentrations of the pollutant methylmercury on pigment coloration in zebra finches (Taeniopygia guttata). First, we tested whether effects of methylmercury on coloration were influenced by timing of exposure. Birds were either exposed developmentally (up to 114 days after hatching), as adults (after reaching sexual maturity), or for their entire life. Bill coloration, which is a carotenoid-based, sexually selected trait, was less red in males with lifetime exposure to methylmercury, compared to controls. Neither adult, nor developmental exposure influenced bill color in adult males, with the possible exception of early exposure of nestlings. Among females, where bill color is not under strong sexual selection, neither lifetime nor adult exposure to methylmercury affected bill color. For males and females, there was no effect of either lifetime or adult methylmercury exposure on coloration of back feathers, which is a non-sexually-dimorphic, melanin-based trait that is not likely the result of sexual selection. This study is a comprehensive experimental test of the proposal that sexually selected traits may be particularly useful bioindicators of the stress imposed by environmental toxins such as methylmercury.

Individual and synergistic effects of male external genital traits in sexual selection.

Male genital traits exhibit extraordinary interspecific phenotypic variation. This remarkable and general evolutionary trend is widely considered to be the result of sexual selection. However, we still do not have a good understanding of whether or how individual genital traits function in different competitive arenas (episodes of sexual selection), or how different genital traits may interact to influence competitive outcomes. Here, we use an experimental approach based on high-precision laser phenotypic engineering to address these outstanding questions, focusing on three distinct sets of micron-scale external (nonintromittent) genital spines in male Drosophila kikkawai Burla (Diptera: Drosophilidae). Elimination of the large pair of spines on the male secondary claspers sharply reduced male ability to copulate, yet elimination of the other sets of spines on the primary and secondary claspers had no significant effects on copulation probability. Intriguingly, both the large spines on the secondary claspers and the cluster of spines on the primary claspers were found to independently promote male competitive fertilization success. Moreover, when large and small secondary clasper spines were simultaneously shortened in individual males, these males suffered greater reductions in fertilization success relative to males whose traits were altered individually, providing evidence for synergistic effects of external genital traits on fertilization success. Overall, the results are significant in demonstrating that a given genital trait (the large spines on the secondary claspers) can function in different episodes of sexual selection, and distinct genital traits may interact in sexual selection. The results offer an important contribution to evolutionary biology by demonstrating an understudied selective mechanism, operating via subtle trait interactions in a post-insemination context, by which genital traits may be co-evolving.

Sexual selection and male-biased size dimorphism in a lineage of lungless salamander (Ampibia: Plethodontidae)

Abstract Evolutionary biologists have long focused on the patterns and causes of sexual size dimorphism (SSD). While female-biased SSD is common among ectotherms, a few lineages predominately exhibit male-biased SSD. One example is the clade of desmognathans, a monophyletic group of two genera within the Plethodontinae of the lungless salamander family Plethodontidae. Members of these two genera have a unique pattern of SSD: males mature earlier and at smaller sizes than females but reach greater maximum sizes. We used comparative phylogenetic methods to test whether SSD in these salamanders is the result of sexual selection on males. Spatial evolutionary and ecological vicariance analysis indicated a significant divergence in SSD associated with the phylogenetic origin of the desmognathans. Phylogenetic least-squares regression across the two most speciose genera of the subfamily determined a significant relationship between SSD and adult sex ratio. While male desmognathans are not sexually dimorphic in head size, they have a unique head morphology that causes their heads to grow more rapidly as their body size increases as compared with the heads of other salamanders. This pattern of allometric growth combines with a powerful bite force and enlarged premaxillary teeth to create formidable weaponry that probably is more responsive to sexual selection.

Triparental inheritance in Dictyostelium

Sex promotes the recombination and reassortment of genetic material and is prevalent across eukaryotes, although our knowledge of the molecular details of sexual inheritance is scant in several major lineages. In social amoebae, sex involves a promiscuous mixing of cytoplasm before zygotes consume the majority of cells, but for technical reasons, sexual progeny have been difficult to obtain and study. We report here genome-wide characterization of meiotic progeny in Dictyostelium discoideum We find that recombination occurs at high frequency in pairwise crosses between all three mating types, despite the absence of the Spo11 enzyme that is normally required to initiate crossover formation. Fusions of more than two gametes to form transient syncytia lead to frequent triparental inheritance, with haploid meiotic progeny bearing recombined nuclear haplotypes from two parents and the mitochondrial genome from a third. Cells that do not contribute genetically to the Dictyostelium zygote nucleus thereby have a stake in the next haploid generation. D. discoideum mitochondrial genomes are polymorphic, and our findings raise the possibility that some of this variation might be a result of sexual selection on genes that can promote the spread of individual organelle genomes during sex. This kind of self-interested mitochondrial behavior may have had important consequences during eukaryogenesis and the initial evolution of sex.

Mating success in fruit flies: courtship interference versus female choice

The outcomes of sexual selection often differ when mating success is determined by male contest rather than female choice. Many studies, however, inferred sexual selection driven by female choice without carefully assessing the role of subtle male aggression. Relying on close-up video analyses, we documented novel courtship interference between male fruit flies, a key model system in research on sexual selection, sexual conflict and speciation. In experiments comparing male mating success under choice (2 males + 1 female) and no-choice (1 male + 1 female) conditions, we found that, in some cases, courtship interference altered male mating success. Both choice and no-choice protocols have known weaknesses. Choice protocols do not control for male–male interactions while no-choice protocols do not allow females to compare and choose between males. To overcome these weaknesses, we developed a new protocol (true-choice), which allows females to freely visit and assess each of two males while preventing direct male–male interactions. Results from the true-choice protocol suggest that traits enhancing male aggression have a greater role in determining mating success in fruit flies. Furthermore, it is possible that the mating system of scramble competition observed in many species should be reclassified as subtle male contest, which can drive sexual selection for aggressive male features.

Ecological variation along the salinity gradient in the Baltic Sea Area and its consequences for reproduction in the common goby.

Although it has become clear that sexual selection may shape mating systems and drive speciation, the potential constraints of environmental factors on processes and outcomes of sexual selection are largely unexplored. Here, we investigate the geographic variation of such environmental factors, more precisely the quality and quantity of nest resources (bivalve shells) along a salinity gradient in the Baltic Sea Area (Baltic Sea, Sounds and Belts, and Kattegat). We further test whether we find any salinity-associated morphological differences in body size between populations of common gobies Pomatoschistus microps, a small marine fish with a resource-based mating system. In a geographically expansive field study, we sampled 5 populations of P. microps occurring along the salinity gradient (decreasing from West to East) in the Baltic Sea Area over 3 consecutive years. Nest resource quantity and quality decreased from West to East, and a correlation between mussel size and male body size was detected. Population density, sex ratios, mating- and reproductive success as well as brood characteristics also differed between populations but with a less clear relation to salinity. With this field study we shed light on geographic variation of distinct environmental parameters possibly acting on population differentiation. We provide insights on relevant ecological variation, and draw attention to its importance in the framework of context-dependent plasticity of sexual selection.

Female Mate Choice Based on Male Nuptial Coloration in Pale Chub,Zacco platypus

Males of many animals exhibit conspicuous secondary sexual traits, which are often the result of sexual selection. During the breeding period of the pale chub (Pisces: Cyprinidae), males show various sexual traits, such as long anal fins, breeding tubercles on the head, and/or conspicuous red and greenish-blue nuptial colorations. Although these conspicuous sexual dimorphisms and dichromatisms indicate that this can serve as a model species for understanding sexual selection, it is unclear whether these male sexual traits are related to female mate choice. This study examined the relationships between female mate choice and male sexual traits under laboratory conditions. In a dichotomous choice experiment, no relationship was found between female preference and male body size, anal fin length or number of breeding tubercles. In addition, female preference was not detected for traits related to the greenish-blue nuptial color of males. Instead, females chose males based on the degree of expression of red nuptial coloration. Such female preference may be useful for selecting high-quality males with good foraging abilities or good immune function related to carotenoids and sexual hormones. The present study suggests that red nuptial coloration of the male pale chub evolved in part through female mate choice.

The evolution of genital shape variation in female cetaceans.

Male genital diversification is likely the result of sexual selection. Female genital diversification may also result from sexual selection, although it is less well studied and understood. Female genitalia are complex among whales, dolphins, and porpoises, especially compared to other vertebrates. The evolutionary factors affecting the diversity of vaginal complexity could include ontogeny, allometry, phylogeny, sexual selection, and natural selection. We quantified shape variation in female genitalia using 2D geometric morphometric analysis, and validated the application of this method to study soft tissues. We explored patterns of variation in the shape of the cervix and vagina of 24 cetacean species (n = 61 specimens), and found that genital shape varies primarily in the relative vaginal length and overall aspect ratio of the reproductive tract. Extensive genital shape variation was partly explained by ontogenetic changes and evolutionary allometry among sexually mature cetaceans, whereas phylogenetic signal, relative testis size, and neonate size were not significantly associated with genital shape. Female genital shape is diverse and evolves rapidly even among closely related species, consistent with predictions of sexual selection models and with findings in invertebrate and vertebrate taxa. Future research exploring genital shape variation in 3D will offer new insights into evolutionary mechanisms because internal vaginal structures are variable and can form complex spirals.

Origin and cross-century dynamics of an avian hybrid zone

BackgroundCharacterizations of the dynamics of hybrid zones in space and time can give insights about traits and processes important in population divergence and speciation. We characterized a hybrid zone between tanagers in the genus Ramphocelus (Aves, Thraupidae) located in southwestern Colombia. We evaluated whether this hybrid zone originated as a result of secondary contact or of primary differentiation, and described its dynamics across time using spatial analyses of molecular, morphological, and coloration data in combination with paleodistribution modeling.ResultsModels of potential historical distributions based on climatic data and genetic signatures of demographic expansion suggested that the hybrid zone likely originated following secondary contact between populations that expanded their ranges out of isolated areas in the Quaternary. Concordant patterns of variation in phenotypic characters across the hybrid zone and its narrow extent are suggestive of a tension zone, maintained by a balance between dispersal and selection against hybrids. Estimates of phenotypic cline parameters obtained using specimens collected over nearly a century revealed that, in recent decades, the zone appears to have moved to the east and to higher elevations, and may have become narrower. Genetic variation was not clearly structured along the hybrid zone, but comparisons between historical and contemporary specimens suggested that temporal changes in its genetic makeup may also have occurred.ConclusionsOur data suggest that the hybrid zone likey resulted from secondary contact between populations. The observed changes in the hybrid zone may be a result of sexual selection, asymmetric gene flow, or environmental change.

Condition dependence of female-specific UV-induced fluorescence in a jumping spider

Male ornaments, commonly explained as being a result of sexual selection, are typically more elaborate than female ornaments. Interestingly, the bright and showy sexually selected traits of some female ornaments, like those of males, might be variable and condition dependent, and hence relate to individual quality. Ultraviolet (UV)-induced fluorescence is one such ornament known to be intricately involved in intraspecific communication in several animals; however, the role of fluorescence in signalling individual quality is unknown. The ornate jumping spider, Cosmophasis umbratica , exhibits female-specific UV-induced fluorescence on its palps to facilitate effective intersex communication but whether the fluorescence informs males of the female's condition and individual quality is unknown. We tested the prediction that UV-induced fluorescence in adult female C. umbratica depended on postmaturation age, mating status and feeding regime. We found that postmaturation age and feeding regime, but not mating status, affected female fluorescence. Middle-aged females were brighter than younger and older females, but the older females had a greener hue; well-fed females were brighter than starved females. We conclude that the UV-induced fluorescence of female C. umbratica is highly condition dependent, highlighting the importance of considering female as well as male ornamentation, particularly when this may have implications for mate choice and the maintenance of coloration in animals.

Postcopulatory sexual selection influences baculum evolution in primates and carnivores.

The extreme morphological variability of the baculum across mammals is thought to be the result of sexual selection (particularly, high levels of postcopulatory selection). However, the evolutionary trajectory of the mammalian baculum is little studied and evidence for the adaptive function of the baculum has so far been elusive. Here, we use Markov chain Monte Carlo methods implemented in a Bayesian phylogenetic framework to reconstruct baculum evolution across the mammalian class and investigate the rate of baculum length evolution within the primate order. We then test the effects of testes mass (postcopulatory sexual selection), polygamy, seasonal breeding and intromission duration on the baculum in primates and carnivores. The ancestral mammal did not have a baculum, but both ancestral primates and carnivores did. No relationship was found between testes mass and baculum length in either primates or carnivores. Intromission duration correlated with baculum presence over the course of primate evolution, and prolonged intromission predicts significantly longer bacula in extant primates and carnivores. Both polygamous and seasonal breeding systems predict significantly longer bacula in primates. These results suggest the baculum plays an important role in facilitating reproductive strategies in populations with high levels of postcopulatory sexual selection.

The Morphological Diversity of Intromittent Organs: An Introduction to the Symposium.

Intromittent organs are structures that enter the female genital tract and deposit sperm; these organs are found in many animal taxa that use internal fertilization. Despite their shared function, they are fantastically diverse morphologically. Many of their species-specific shape differences are likely the result of sexual selection and coevolution between male and female reproductive tracts, but a growing number of studies have identified other factors that can also affect their functional anatomy. In this symposium, we united scientists who combine morphological methods with contemporary molecular, phylogenetic, and imaging techniques to study the reproductive performance of intromittent organs in invertebrate and vertebrate model systems. The result was a collection of studies discussing competing selective pressures that act on these structures, including the effects of life history, genes and development, sexual conflict, ecological interactions, the biomechanics of copulation, and phenotypic plasticity. There was also an overwhelming consensus that a full understanding of intromittent organ evolution will not be possible without complimentary studies of morphology and function in female reproductive tracts.

The influence of iridescent coloration directionality on male tree swallows’ reproductive success at different breeding densities

Conspicuous coloration in males of numerous bird species has been related to sexual selection. However, iridescent coloration is a complex trait that has received little attention despite its potential importance as a signal of individual condition. Directionality, the change in brightness when the animal moves under direct sunlight, has never been linked to fitness although being an integral part of iridescent coloration. Using 214 male tree swallows (Tachycineta bicolor) from a 2-year study, we investigated how different components of iridescent coloration were related to four measures of fitness (number of extra-pair and within-pair young produced, proportion of within-pair young in the nest and annual reproductive success) across different breeding densities. In addition to classical components of coloration (hue, brightness, saturation), we used directionality—measured as an angular breadth of color reflection—to quantify the iridescent coloration of male crown and back. Our results showed that all components of iridescent coloration we studied were related to at least one of the four measures of fitness. A negative association was detected between directionality and the number of within-pair young produced, suggesting that this plumage characteristic could be a signal of paternal care. Crown and back coloration were associated to different fitness components, and density modulated the slope of some of these relationships. Altogether, our results showed that different selective pressures could act on the multiple components of iridescent coloration via both within-pair and extra-pair components of reproductive success. Also, environmental conditions like breeding density are important factors influencing sexual selection processes. The idea that colorful plumage in males is the result of sexual selection is widely recognized. However, evidence of sexual selection on iridescent plumage is scarce. In birds displaying iridescent plumage, the brightness change occurring when the bird moves, called directionality, is striking and could be informative for females when choosing a mate. Using 214 male tree swallows, we found that directionality was related to the number of young produced by a male. As nests were distributed in 40 different farms, a high variability of breeding densities occurred in the study system. Breeding density highly influenced the relationship between color components of iridescent plumage and the number of young produced by a male. This study emphasizes the importance to quantify the angular properties of iridescent plumage as well as to take into account breeding density when studying sexual selection.

Sexual dimorphism and physiological correlates of horn length in a South African isopod crustacean

Although isopod crustaceans frequently show sexual dimorphism in body size, sexual differences in other non-reproductive (secondary sexual) traits have been rarely studied. Furthermore, little is known about the physiological correlates of variation in the expression of sexually dimorphic traits in animals generally. Here, we show that the unusual dorsal horns of the South African horned isopod Deto echinata exhibit significantly different allometric scaling relationships with body size in males versus females. Not only are the horns of adult males substantially longer than those of adult females but also their log–log scaling slope with body length is significantly steeper than that of females and juveniles. Furthermore, in males relative horn length is positively correlated with body condition, as estimated by body mass relative to body length, and with resting metabolic (CO2 release) rate, also adjusted to body length. However, although showing a weak positive trend, the relative horn length of males is not significantly correlated with body length adjusted active metabolic rate. It is also not significantly correlated with the relative rates of whole body or cuticular water loss rates or with two measures of activity level. We hypothesize that the sexual dimorphism of horn length in D. echinata is the result of sexual selection and that horn length is a reliable indicator of the ability of a male to acquire and process resources, which in turn may be critical to female mate choice and (or) male–male competition for mates. However, this hypothesis requires further testing based on direct observations of female mate choice and male–male behavioral interactions, which have not yet been carried out.

The importance of being yellow: visual over chemical cues in gender recognition in a social wasp

Differences in male and female phenotypes are often the results of sexual selection. Over the years, a vast number of studies investigated how and why the 2 sexes differ in their physical appearance, reaching the conclusion that peculiar visual traits, signals, or ornaments usually evolve under the pressure of sexual selection to mediate intrasexual competition and mate choice. In social contexts, however, males and females can hold different roles and social interactions may depend on the individual gender. The female-dominated hymenopteran societies represent a fascinating scenario to investigate recognition and communication among individuals of different genders outside a common sexual selection framework because sterile female workers typically do not mate and are not attracted to males. Here, we used laboratory bioassays (lure presentation experiments) to evaluate the ability of Polistes dominula workers to discriminate between individuals of the 2 genders, investigating the relevance of the chemical and visual cues potentially involved in such process. Our results showed that P. dominula workers are able to discriminate between the sexes and visual cues rather than chemical ones are responsible for such discrimination.