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One hundred fifty years ago Darwin published The Descent of Man, and Selection in Relation to Sex , in which he presented his theory of sexual selection with its emphasis on sexual beauty. However, it was not until 50 y ago that there was a renewed interest in Darwin’s theory in general, and specifically the potency of mate choice. Darwin suggested that in many cases female preferences for elaborately ornamented males derived from a female’s taste for the beautiful, the notion that females were attracted to sexual beauty for its own sake. Initially, female mate choice attracted the interest of behavioral ecologists focusing on the fitness advantages accrued through mate choice. Subsequent studies focused on sensory ecology and signal design, often showing how sensory end organs influenced the types of traits females found attractive. Eventually, investigations of neural circuits, neurogenetics, and neurochemistry uncovered a more complete scaffolding underlying sexual attraction. More recently, research inspired by human studies in psychophysics, behavioral economics, and neuroaesthetics have provided some notion of its higher-order mechanisms. In this paper, I review progress in our understanding of Darwin’s conjecture of “a taste for the beautiful” by considering research from these diverse fields that have conspired to provide unparalleled insight into the chooser’s mate choices.more » « less
Sexual conflict over the indirect benefits of mate choice may arise when traits in one sex limit the ability of the other sex to freely choose mates but when these coercive traits are not necessarily directly harmful (i.e. forced fertilization
per se). Although we might hypothesize that females can evolve resistance in order to retain the indirect, genetic benefits (reflected in offspring attractiveness) of mating with attractive males, up to now it has been difficult to evaluate potential underlying mechanisms. Traditional theoretical approaches do not usually conceptually distinguish between female preference for male mating display and female resistance to forced fertilization, yet sexual conflict over indirect benefits implies the simultaneous action of all of these traits. Here, we present an integrative theoretical framework that draws together concepts from both sexual selection and sexual conflict traditions, allowing for the simultaneous coevolution of displays and preferences, and of coercion and resistance. We demonstrate that it is possible for resistance to coercion to evolve in the absence of direct costs of mating to preserve the indirect benefits of mate choice. We find that resistance traits that improve the efficacy of female mating preference can evolve as long as females are able to attain some indirect benefits of mating with attractive males, even when both attractive and unattractive males can coerce. These results reveal new evolutionary outcomes that were not predicted by prior theories of indirect benefits or sexual conflict.
Mating with another species is often maladaptive because it generally results in no or low-fitness offspring. When hybridization is sufficiently costly, individuals should avoid mating with heterospecifics even if it reduces their ability to mate with high-quality conspecifics that resemble heterospecifics. Here, we used spadefoot toads, Spea multiplicata, to evaluate whether females alter their preferences for conspecific male sexual signals (call rate) depending on heterospecific presence. When presented with conspecific signals against a background including both conspecific and heterospecific signals, females preferred male traits that were most dissimilar to heterospecifics—even though these signals are potentially associated with lower-quality mates. However, when these same females were presented with a background that included only conspecific signals, some females switched their preferences, choosing conspecific signals that were exaggerated and indicative of high-quality conspecific mates. Because only some females switched their preferences between these two chorus treatments, there was no population-level preference for exaggerated conspecific male signals in the absence of heterospecifics. These results show that hybridization risk can alter patterns of mate choice and, consequently, sexual selection on male signals. Moreover, they emphasize that the strength and expression of reproductive barriers between species (such as mate choice) can be context-dependent.more » « less
Males in many species have elaborated sexual traits that females strongly prefer, and these traits often conspicuously differ among species. How novel preferences and traits originate, however, is a challenging evolutionary problem because the initial appearance of only the female preference or only the male trait should reduce the ability to find a suitable mate, which could reduce fitness for individuals possessing those novel alleles. Here, we present a hypothesis for how novel preferences, as well as the novel male traits that females prefer, can originate, be favoured and spread in polyandrous species. Novel preference mutations can arise as ‘veiled preferences’ that are not expressed when the corresponding male trait is not present in the population, allowing preferences to be hidden from selection, and thus persist. In those cases when a male trait is present, veiled preferences provide a selective advantage, and females disproportionately produce offspring from preferred males through either mate choice or cryptic female choice. This tips the fitness advantage for novel males, allowing both preference and trait to spread, and limiting selection against them in the absence of the corresponding trait or preference.
Animals often communicate in complex, heterogeneous environments, leading to hypothesized selection for increased detectability or discriminability in signaling traits. The extent to which secondary sexual ornaments have evolved to overcome the challenges of signaling in complex environments, however, remains understudied, especially in comparison to their role as indicator traits. This study tested the hypothesis that the condition-dependent secondary sexual ornamentation in the wolf spider Rabidosa rabida functions to increase detectability/discriminability in visually complex environments. We predicted that male ornamentation would interact with the complexity of the signaling environment to affect male mating success. In particular, we expected ornaments to confer a greater mating advantage when males courted in visually complex environments. To test this, we artificially manipulated male foreleg ornamentation (present/absent) and ran repeated-measures mating trials across laboratory microcosms that represented simple versus complex visual signaling environments. Microcosm visual complexity differed in their background pattern, grass stem color, and grass stem placement. We found that ornamented males mated more often and more quickly than unornamented males across both environments, but we found no support for an ornament-by-environment interaction. Male courtship rate, however, did interact with the signaling environment. Despite achieving the same level of mating success across signaling environments, ornamented males courted less rapidly in complex versus simple environments, although environmental complexity had no influence on unornamented male courtship rates. Our results suggest that the visual complexity of the signaling environment influences the interactive influence of ornamentation and dynamic visual courtship on female mate choice.