Operational Sex Ratio but Not Density Affects Sexual Selection in a Fish

Abstract

The operational sex ratio (OSR) and density are considered important factors affecting the strength of sexual selection. Although there is increasing evidence that OSR and density affect the potential for sexual selection, few studies have addressed whether this is realized in phenotypic selection and how the two factors interact. We manipulated OSR (three levels) and male density (two levels) in 36 experimental breeding populations of Gobiusculus flavescens-a fish with paternal care. We measured mating competition behavior, the opportunity for selection (I), and selection on four morphological traits in males. We found sexual selection on two male traits, with the strongest selection being 20% of I. As predicted from OSR theory, increasing female scarcity caused males to become more competitive, concomitant with an increase in I and selection on morphological traits. Model simulations of I based on random mating (I min ) and maximum mate monopolization (I max ) demonstrated that the potential for sexual selection was close to its theoretical maximum across the range of OSRs. However, male density and its interaction with the OSR did not affect sexual selection. We argue that a multifaceted approach, combining mating behavior and selection analyses, can help us to understand how ecological factors affect sexual selection.

Dense, small and male-biased cages exacerbate male–male competition and reduce female choosiness in Bicyclus anynana

“…number of attempts) with increasing bias towards males, as expected by a wealth of empirical and theoretical studies (empirical, e.g. Carrillo, Danielson-François, Siemann, & Meffert, 2012;Forsgren et al, 2004;Head et al, 2007;de Jong, Forsgren, Sandvik, & Amundsen, 2012;Wacker et al, 2013;theoretical, Emlen & Oring, 1977;Kokko & Rankin, 2006;Kvarnemo & Ahnesj€ o, 1996). As male courtship efforts did not depend on density, we inferred that the increase in male courtship was due to a higher relative number of males and not to a higher mate encounter rate, which shows that the level of courtship activity was directly due to the level of maleemale competition.…”

“…One thus needs to manipulate OSR and density separately to be able to predict the consequences of their potentially complex interactions on mate competition and mating preference. So far, few empirical studies have attempted to do so both in invertebrates (Alonso-Pimentel & Papaj, 1996;Arnqvist, 1992;Janowitz & Fischer, 2012;Saeki, Kruse, & Switzer, 2005;Smith, 2007;Wang, He, Yang, Hedderley, & Davis, 2009;Wang, Yang, & Hedderley, 2008) and in vertebrates (Aronsen, Berglund, Mobley, Ratikainen, & Rosenqvist, 2013;Dreiss, Cote, Richard, Federici, & Clobert, 2010;Elmberg, 1991;Head et al, 2007;de Jong, Wacker, Amundsen, & Forsgren, 2009;Lu, Ma, Fan, & Yu, 2010;Wacker et al, 2013). Second, it is crucial to test mate competition and mating preference in the social environment in which the populations evolved and adapted, which requires using the OSR and density encountered by natural populations in the wild (Fromhage, Elgar, & Schneider, 2005;Fromhage, McNamara, & Houston, 2008;Kokko & Jennions, 2008).…”

Too many men: the violence problem?

“…In fact, there is no apparent patterning of the societies in terms of type or stability of marriage, or indeed of the economy (farming, foraging, or herding), although more systematic comparative analysis with bigger samples using individual level data is warranted [28,29]. Furthermore, it is worth noting that, in nonhumans, higher rates of polygyny do not necessarily mean greater sexual selection on males [32,33].…”

“…Much of the logic above assumes a tradeoff between parenting effort and mating effort, which is not always the case [96]. In some species, providing parental care can be a key element of the mate competition strategy of a male, as in two-spotted goby (Gobiusculus flavescens) [33]. In many human populations, controlling resources enhances a man's mating success and the survival of his children [50].…”

The effects of social experience with varying male availability on female mate preferences in a wolf spider

“…Bencounter rate^) as well the context of male courtship (Spence and Smith 2005), copulation duration (Alonso-Pimentel and Papaj 1996), and the opportunity for sexual selection (Wacker et al 2013). Male zebrafish, Danio rerio, alter their courtship rates in response to changes in the adult sex ratio, but only when the overall population density is high (Spence and Smith 2005).…”