Role Of Sexual Selection Research Articles

Odour cues from suitors' nests determine mating success in a fish.

Animals use a range of sensory cues for finding food, avoiding predators and choosing mates. In this regard, the aquatic environment is particularly suitable for the use of olfactory and other chemical cues. Nevertheless, mate choice research, even on aquatic organisms, has focused on visual signals, while chemical cues relevant in sexual selection have been assumed to be 'intrinsic' excretions of mate candidates. Here, using the sand goby Pomatoschistus minutus, a small fish with paternal egg care, we investigated the possibility that 'extrinsic' chemical cues in the males' nests could also have a significant contribution to mating success. We found that females strongly avoided laying eggs into nests subject to the odour of Saprolegnia water moulds (an egg infection) and that this effect was independent of the females' initial, visually based preference for males. To the best of our knowledge, this is the first study to show that chemical cues related to parental failure can play a large role in sexual selection.

Gazing at a giraffe gyroscope: where are we going?

AbstractGiraffe are popular animals to watch while on wildlife safaris, and feature prominently in zoos, advertisements, toys and cartoons. Yet, until recently, few field studies have focused on giraffe. We introduce this giraffe topic issue with a review essay that explores five primary questions: How many (sub) species of giraffe exist? What are the dynamics of giraffe herds? How do giraffe communicate? What is the role of sexual selection in giraffe reproduction? How many giraffe reside in Africa? A confluence of causes has produced drastic declines in giraffe population numbers in Africa, and we conclude that guiding giraffe conservation plans depends upon evaluation of the five key quandaries that we pose.

Condition-dependence, pleiotropy and the handicap principle of sexual selection in melanin-based colouration.

The signalling function of melanin-based colouration is debated. Sexual selection theory states that ornaments should be costly to produce, maintain, wear or display to signal quality honestly to potential mates or competitors. An increasing number of studies supports the hypothesis that the degree of melanism covaries with aspects of body condition (e.g. body mass or immunity), which has contributed to change the initial perception that melanin-based colour ornaments entail no costs. Indeed, the expression of many (but not all) melanin-based colour traits is weakly sensitive to the environment but strongly heritable suggesting that these colour traits are relatively cheap to produce and maintain, thus raising the question of how such colour traits could signal quality honestly. Here I review the production, maintenance and wearing/displaying costs that can generate a correlation between melanin-based colouration and body condition, and consider other evolutionary mechanisms that can also lead to covariation between colour and body condition. Because genes controlling melanic traits can affect numerous phenotypic traits, pleiotropy could also explain a linkage between body condition and colouration. Pleiotropy may result in differently coloured individuals signalling different aspects of quality that are maintained by frequency-dependent selection or local adaptation. Colouration may therefore not signal absolute quality to potential mates or competitors (e.g. dark males may not achieve a higher fitness than pale males); otherwise genetic variation would be rapidly depleted by directional selection. As a consequence, selection on heritable melanin-based colouration may not always be directional, but mate choice may be conditional to environmental conditions (i.e. context-dependent sexual selection). Despite the interest of evolutionary biologists in the adaptive value of melanin-based colouration, its actual role in sexual selection is still poorly understood.

Geographic variation in sexual selection and implications for speciation in the Barn Swallow

Barn Swallows (Hirundo rustica), a group of passerine birds comprised of six closely related subspecies, are well known throughout their nearly worldwide distribution, in part because of their close association with human settlements. A tractable species for both individual-based and population-level studies, Barn Swallows are a prominent model system in evolutionary, ecological, and behavioral research. Here we review work on sexual selection and population divergence in this species complex, focusing on comparative studies among populations and subspecies. We summarize variation in the targets of mate choice and in the information conveyed by sexually selected traits, and conclude that the benefits advertised by different traits may vary geographically. Finally, we consider the role of sexual selection as a driver of population divergence in this widespread and phenotypically variable species complex.

Positive selection at a seminal fluid gene within a QTL for conspecific sperm precedence.

The role of sexual selection in driving the rapid evolution of male reproductive proteins has been tested in a wide variety of organisms. Sperm competition is a form of postmating sexual selection that can contribute to reproductive isolation between species by biasing the proportion of progeny fathered by conspecific over heterospecific males. This phenomenon is known as conspecific sperm precedence (CSP). A previous quantitative trait loci study between Drosophila simulans and D. sechellia identified a locus associated with CSP within the second chromosome centered at the 53 cytogenetic map position. Male accessory gland proteins (ACPs) are associated with triggering postmating physiological responses in D. melanogaster females that can contribute to differential male reproductive success. Moreover, a large number of ACPs evolve rapidly and under positive selection among closely-related species of Drosophila. Here we have sequenced five candidate Acp genes (Acp53C14a, Acp53C14b, Acp53C14c, Acp53Ea and Acp54A1) within the previously mapped D. simulans-D. sechellia CSP locus from different D. simulans and D. sechellia strains. Polymorphism data analysis shows evidence of a selective sweep at Acp53Ea within D. simulans. In the context of CSP, the combined use of polymorphism and interspecies sequence divergence shows that Acp53C14c gene tree topology separates D. simulans and D. sechellia. Moreover, Acp53C14c is the only gene showing evidence of positive selection with five fixed amino acid substitutions between species. Our results highlight Acp53C14c as a candidate gene for future gene targeting studies to elucidate its role in CSP between D. simulans and D. sechellia.

Let's face it--complex traits are just not that simple.

Let's face it--complex traits are just not that simple.

Sexual Dimorphism in the Flowers of <I>Aegiphila odontophylla</I> (Lamiaceae)

Abstract Little is known about the sexuality of the woody Neotropical genus Aegiphila. For a long time species of Aegiphila were thought to be heterostylous, but more recently it has been reported that a few species are dioecious and suggested that likely most Aegiphila are functionally dioecious. In this note, dioecy is confirmed in Aegiphila odontophylla from live plants in the Talamanca mountains in Costa Rica. Further, comparison of total flower size revealed that male and female reproductive structures are displayed at similar heights, likely resulting in accurate pollen uptake and delivery by pollinators. The length of the corolla tube as an estimate of flower showiness on the other hand was significantly different between male and female individuals. Male individuals had longer corolla tubes, suggesting a possible role for sexual selection in the evolution of floral dimorphism in this species.

Pervasive reinforcement and the role of sexual selection in biological speciation.

Sexual selection has been widely implicated as a driver of speciation. However, allopatric forms are often defined as species based on divergence in sexually selected traits and it is unclear how much such trait differences affect reproductive isolation upon secondary contact, the defining feature of biological species. We show that in birds, divergence in song and plumage in allopatry corresponds poorly with whether species mate assortatively in hybrid zones and argue that this is because many other factors besides trait divergence affect propensity to hybridize, including rarity of conspecific mates and choice based on territory rather than male traits. We then present a general model for the establishment of sympatry that assumes a period of differentiation in allopatry followed by secondary contact and often hybridization, with hybridization subsequently reduced by reinforcement of mate preferences. We suggest that reinforcement commonly operates by a narrowing of a "window of recognition" for traits that are different between the species, rather than evolution of the traits themselves. Our arguments imply that it is important to study postmating as well as premating reproductive isolation in limiting sympatry and suggest that studies of reinforcement should focus on evolution of female preferences for diagnostic traits, rather than evolution of traits per se.

The Role of Sexual Selection in the Evolution of Chemical Signals in Insects.

Chemical communication is the most ancient and widespread form of communication. Yet we are only beginning to grasp the complexity of chemical signals and the role they play in sexual selection. Focusing on insects, we review here the recent progress in the field of olfactory-based sexual selection. We will show that there is mounting empirical evidence that sexual selection affects the evolution of chemical traits, but form and strength of selection differ between species. Studies indicate that some chemical signals are expressed in relation to an individual’s condition and depend, for example, on age, immunocompetence, fertility, body size or degree of inbreeding. Males or females might benefit by choosing based on those traits, gaining resources or “good genes”. Other chemical traits appear to reliably reflect an individual’s underlying genotype and are suitable to choose a mating partner that matches best the own genotype.

Patterns of Male Breeding Color Variation Differ across Species, Populations, and Body Size in Rainbow and Orangethroat Darters

Sexually dimorphic coloration has been widely suggested to play a role in sexual selection and speciation. Animal colors can originate from several different biochemical pathways, which may underlie different patterns of selection and diversification. Darters of the speciose genus Etheostoma exhibit substantial diversity in male breeding coloration. We used digital photography and image software to comprehensively quantify male coloration in the Rainbow Darter (Etheostoma caeruleum) and the Orangethroat Darter (E. spectabile). Color traits differed across species, populations, and body sizes, with size differences contributing the most to individual color variation. The bluish colors were overall more strongly correlated with size than the reddish colors. Conversely, the reddish colors tended to be less correlated with size and better indicators of species and population identity. Finally, we determined that the bluish colored tissue contained a chromoprotein pigment, and that the reddish colored tissue c...

Sex‐Specific Associations Between Nest Defence, Exploration and Breathing Rate in Breeding Pied Flycatchers

AbstractCorrelations between behavioural traits constrain animals to a limited range of behavioural choices and set a limit to the available variation in behavioural phenotype of a population. These constraints are especially important during stressful situations, potentially limiting the ability to cope with stress appropriately. As yet, very little consideration has been given to a possible role for sexual selection in maintaining differences in behavioural stability within individuals: sex‐specific differences in behavioural correlations have been seldom studied, especially in the wild. In this field study, we investigated associations between neophobia (latency to enter nest in the presence of a novel object), nest defence (response to a model predator) and breathing rate in response to handling in breeding pied flycatchers (Ficedula hypoleuca). We did not find any significant difference in antipredator responses between males and females, which indicates low sexual conflict over parental care in the pied flycatcher. However, females were more neophobic than males, while males and females did not differ in their breathing rates. Further, our study demonstrated a strong positive correlation between nest defence behaviour and neophobia in male, but not in female pied flycatchers. Males that defended their nest more had lower breathing rate and higher latency to resume nestling feeding after encountering a predator decoy than males that mobbed less intensely. We found only weak evidence that nest partners might affect each other's behaviour in these contexts.

Do social mating systems limit maternal immune investment in shorebirds?

Across mating systems, females differ in the amount of resources they invest in offspring. For example, polyandrous females invest in acquiring multiple matings rather than providing parental care. We examined how the amount of maternal immune investment, measured as immunoglobulin Y and lysozyme activity in eggs, was influenced by female role across three social mating systems (polyandry, polygyny, and monogamy) in shorebirds. We predicted that polyandry should impose the greatest costs on the ability to provision eggs and monogamy, where females receive benefits from biparentality, the least. Contrary to our predictions, levels of maternally derived egg immune constituents were consistently high across measures in the polyandrous species and low in the monogamous species. Our results may support a link with pace-of-life where developmental costs are greater than the energetic costs of provisioning eggs, and (or) a role for sexual selection acting on maternal immune investment.

Role of sexual selection in speciation in Drosophila

The power of sexual selection to drive changes in the mate recognition system through divergence in sexually selected traits gives it the potential to be a potent force in speciation. To know how sexual selection can bring such type of divergence in the genus Drosophila, comparative studies based on intra- and inter-sexual selection are documented in this review. The studies provide evidence that both mate choice and male-male competition can cause selection of trait and preference which thereby leads to divergence among species. In the case of intrasexual selection, various kinds of signals play significant role in affecting the species mate recognition system and hence causing divergence between the species. However, intrasexual selection can bring the intraspecific divergence at the level of pre- and post-copulatory stage. This has been better explained through Hawaiian Drosophila which has been suggested a wonderful model system in explaining the events of speciation via sexual selection. This is due to their elaborate mating displays and some kind of ethological isolation persisting among them. Similarly, the genetic basis of sexually selected variations can provide yet another path in understanding the speciation genetics via sexual selection more closely.

Sexual selection acting on a speciation trait in darters (Percidae: Etheostoma)

Despite theoretical support linking sexual selection for elaborate coloration and behavioral isolation, few empirical examples clearly demonstrate that the sexually dichromatic signals responsible for behavioral isolation between species are, or have been, subject to sexual selection within species. The present study investigates sexual selection on male nuptial coloration in Etheostoma barrenense, a darter species for which male color has been shown in a previous study to contribute to behavioral isolation from a sympatric congener. Through the use of motorized model fish, we demonstrate that female E. barrenense discriminate between the orange and red body hues of conspecific males and exhibit an association preference for orange over red models. Combined with the results from a previous study, these data provide evidence for a link between sexual selection and behavioral isolation and by extension for a role of sexual selection in speciation. A post hoc analysis of the colors modeled in darter visual space suggests that quantifying signal values as they are perceived, rather than expressed, provide a promising way of linking sexual selection and behavioral isolation.

Attunement to the fertility status of same-sex rivals: women's testosterone responses to olfactory ovulation cues

Evolutionary theories of mating suggest that changes in fertility across the menstrual cycle play an important role in sexual selection. In line with this framework, the current research examined whether olfactory cues to the fertility of a same-sex rival would prompt hormonal signs of intrasexual competition in women. Women exposed to the scent of another woman close to ovulation subsequently displayed higher levels of testosterone than women exposed to the scent of a woman far from ovulation. Whereas women exposed to the scent of a woman in the mid-luteal phase displayed sizable decreases in testosterone over time, no such decline was observed among women exposed to the scent of a woman near ovulation. Thus, olfactory cues signaling a rival's heightened level of fertility were associated with endocrinological responses in women that could be linked to intrasexual competition.

Through their eyes: selective attention in peahens during courtship

Conspicuous, multicomponent ornamentation in male animals can be favored by female mate choice but we know little about the cognitive processes females use to evaluate these traits. Sexual selection may favor attention mechanisms allowing the choosing females to selectively and efficiently acquire relevant information from complex male display traits and, in turn, may favor male display traits that effectively capture and hold female attention. Using a miniaturized telemetric gaze-tracker, we show that peahens (Pavo cristatus) selectively attend to specific components of peacock courtship displays and virtually ignore other, highly conspicuous components. Females gazed at the lower train but largely ignored the head, crest and upper train. When the lower train was obscured, however, females spent more time gazing at the upper train and approached the upper train from a distance. Our results suggest that peahens mainly evaluate the lower train during close-up courtship but use the upper train as a long-distance attraction signal. Furthermore, we found that behavioral display components (train rattling and wing shaking) captured and maintained female attention, indicating that interactions between display components may promote the evolution of multicomponent displays. Taken together, these findings suggest that selective attention plays a crucial role in sexual selection and likely influences the evolution of male display traits.

Symmetry of black wingtips is related to clutch size and integument coloration in Black-legged Kittiwakes (Rissa tridactyla)

Fluctuating asymmetry has been suggested to be a phenotypic marker of developmental stability and is often seen as an indicator of overall quality. However, its role in sexual selection has been debated. To determine the potential role of black wingtip asymmetry in sexual selection in Black-legged Kittiwakes (Rissa tridactyla), we investigated whether symmetry was correlated with reproductive success and integument coloration, a trait probably sexually selected in this species. We found that, in males, asymmetry was associated with low clutch size and brood size but was independent of fledging success, which suggests that wingtip symmetry may reflect fertility in males. Asymmetry of black wingtip was also associated with duller integument, which emphasizes the potential importance of integument color in indicating individual quality. Further studies are needed to determine whether Black-legged Kittiwakes can discriminate between asymmetric and symmetric birds and use it as a cue in mate choice or intrasexual competition.

Wing whiteness as an indicator of age, immunocompetence, and testis size in the Eurasian Black-Billed Magpie (Pica pica)

Determining how phenotypic traits covary within individuals can offer information on the underlying functional interactions of complex phenotypes and the mechanisms that promote them. We investigated covariation of the white wing patch of the Eurasian Black-billed Magpie (Pica pica) with age, sex, feather wear, spleen size, parasite infection, and testis size to evaluate whether this trait is indicative of individual quality. The white wing area was larger in adults than in second-year individuals, in males and females with larger spleens and lower helminth parasite burdens, and in males with larger testes. In addition, feather wear scores were positively correlated with black melanized areas at the tips of feathers. Our results suggest that wing whiteness reflects age, immune capacity, and feather quality in both sexes and reproductive potential in males. Therefore, this character may play a role in sexual selection by signaling individual quality.

Key ornamental innovations facilitate diversification in an avian radiation

Patterns of biodiversity are often explained by ecological processes, where traits that promote novel ways of interacting with the environment (key innovations) play a fundamental role in promoting diversification. However, sexual selection and social competition can also promote diversification through rapid evolution of ornamental traits. Because selection can operate only on existing variation, the tendency of ornamental traits to constrain or enable the production of novel phenotypes is a crucial but often overlooked aspect of diversification. Starlings are a speciose group characterized by diverse iridescent colors produced by nanometer-scale arrays of melanin-containing organelles (melanosomes) that play a central role in sexual selection and social competition. We show that evolutionary lability of these colors is associated with both morphological and lineage diversification in African starlings. The solid rod-like melanosome morphology has evolved in a directional manner into three more optically complex forms that can produce a broader range of colors than the ancestral form, resulting in (i) faster color evolution, (ii) the occupation of novel, previously unreachable regions of colorspace, and ultimately (iii) accelerated lineage diversification. As in adaptive radiations, key innovations in ornament production can provide high phenotypic trait variability, leading to dramatic effects on the tempo and mode of diversification.

RETRACTED: Men’s music ability and attractiveness to women in a real-life courtship context

This experiment tested the assumption that music plays a role in sexual selection. Three hundred young women were solicited in the street for their phone number by a young male confederate who held either a guitar case or a sports bag in his hands or had no bag at all. Results showed that holding a guitar case was associated with greater compliance to the request, thus suggesting that musical practice is associated with sexual selection.