Endless forms of sexual selection

Abstract

In recent years, the field of sexual selection has exploded, with advances in theoretical and empirical research complementing each other in exciting ways. This perspective piece is the product of a “stock-taking” workshop on sexual selection and sexual conflict. Our aim is to identify and deliberate on outstanding questions and to stimulate discussion rather than provide a comprehensive overview of the entire field. These questions are organized into four thematic sections we deem essential to the field. First we focus on the evolution of mate choice and mating systems. Variation in mate quality can generate both competition and choice in the opposite sex, with implications for the evolution of mating systems. Limitations on mate choice may dictate the importance of direct vs. indirect benefits in mating decisions and consequently, mating systems, especially with regard to polyandry. Second, we focus on how sender and receiver mechanisms shape signal design. Mediation of honest signal content likely depends on integration of temporally variable social and physiological costs that are challenging to measure. We view the neuroethology of sensory and cognitive receiver biases as the main key to signal form and the ‘aesthetic sense’ proposed by Darwin. Since a receiver bias is sufficient to both initiate and drive ornament or armament exaggeration, without a genetically correlated or even coevolving receiver, this may be the appropriate ‘null model’ of sexual selection. Thirdly, we focus on the genetic architecture of sexually selected traits. Despite advances in modern molecular techniques, the number and identity of genes underlying performance, display and secondary sexual traits remains largely unknown. In-depth investigations into the genetic basis of sexual dimorphism in the context of long-term field studies will reveal constraints and trajectories of sexually selected trait evolution. Finally, we focus on sexual selection and conflict as drivers of speciation. Population divergence and speciation are often influenced by an interplay between sexual and natural selection. The extent to which sexual selection promotes or counteracts population divergence may vary depending on the genetic architecture of traits as well as the covariance between mating competition and local adaptation. Additionally, post-copulatory processes, such as selection against heterospecific sperm, may influence the importance of sexual selection in speciation. We propose that efforts to resolve these four themes can catalyze conceptual progress in the field of sexual selection, and we offer potential avenues of research to advance this progress.

Visible beyond Violet: How Butterflies Manage Ultraviolet

“…Kemp [ 78 ] found that in Eurema hecabe , male UV brightness correlates with their body size and, interestingly, also with the size of their mate. This supports the hypothesis for the complexity of sexual interactions in polyandrous pierid butterflies, including, for instance, potential assortative mating [ 8 , 85 ]. Furthermore, one study found multiple quality-revealing sexual ornaments (nest features, plumage quality, ecoparasite load, body size) in bowerbirds, suggesting that bowers are an extension of the male phenotype that females can use to assess male quality [ 86 ].…”

“…Female preference for males with brighter UV patterns was also found in Hypolimnas bolina [ 76 ]. A key prediction of the honest signalling theory is that the expression of directionally selected sexual traits should tightly co-vary with the condition of the phenotype [ 25 , 85 ]. This phenomenon is known as ‘condition-dependence’ [ 102 ].…”

Origins of music in credible signaling

“…In addition to credibility, multiple selection pressures can shape signals, including biases in the sensory systems of receivers; receiver abilities to discriminate signals; the structure of the environment; social challenges; and arms races between signalers and receivers (Krebs & Dawkins 1984), where signalers are selected to produce the signal at lower cost and receivers are selected to better discriminate the quality of signalers (Bradbury & Vehrencamp 1998;Cummings & Endler 2018;Doorn & Weissing 2006;Hill 1994;Lindsay et al 2019;McCoy & Haig 2020).…”

Behavioral Variation in the Pygmy Halfbeak Dermogenys collettei: Comparing Shoals With Contrasting Ecologies

“…Differences between the sexes also play a major role in determining among-population variation in socio-sexual and locomotor behaviors. Classically defined sex roles suggest that sexual selection should be stronger on males than females, as lower costs of gamete investment for males lead to greater benefits of multiple mating (Bateman, 1948;Lindsay et al, 2019). Consequently, males are generally expected to invest more of their time and energy engaged in courtship behaviors to attract partners (inter-sexual selection) and agonistic behaviors toward rivals to compete for reproductive opportunities (intra-sexual selection; Andersson, 1994).…”