The role of male contest competition over mates in speciation

Abstract

Research on the role of sexual selection in the speciation process largely focuses on the diversifying role of mate choice. In particular, much attention has been drawn to the fact that population divergence in mate choice and in the male traits subject to choice directly can lead to assortative mating. However, male contest competition over mates also constitutes an important mechanism of sexual selection. We review recent empirical studies and argue that sexual selection through male contest competition can affect speciation in ways other than mate choice. For example, biases in aggression towards similar competitors can lead to disruptive and negative frequency-dependent selection on the traits used in contest competition in a similar way as competition for other types of limited resources. Moreover, male contest abilities often trade-off against other abilities such as parasite resistance, protection against predators and general stress tolerance. Populations experiencing different ecological conditions should therefore quickly diverge non-randomly in a number of traits including male contest abilities. In resource based breeding systems, a feedback loop between competitive ability and habitat use may lead to further population divergence. We discuss how population divergence in traits used in male contest competition can lead to the build up of reproductive isolation through a number of different pathways. Our main conclusion is that the role of male contest competition in speciation remains largely scientifically unexplored.

Asymmetric dominance and asymmetric mate choice oppose premating isolation after allopatric divergence

“…In contrast to numerous studies on intra- and intersexual selection pressures within populations, empirical evidence regarding how and to what degree interactions between mate preferences and intrasexual competition affect assortative mating and speciation processes is limited (Qvarnström et al. 2012). In resource-based breeding systems, for instance, interspecific competition can on the one hand lead to habitat segregation and hence strengthen premating isolation (Vallin and Qvarnström 2011), but can on the other hand interfere with assortative mating by constraining the choice of conspecific males.…”

The evolutionary loss of a badge of status alters male competition in three-spine stickleback

“…The pattern of increased aggression toward opposite type males differs from much previous work on aggression biases (Qvarnstrom et al 2012). Several recent investigations show instead that aggression is biased toward similar competitors (e.g., Dijkstra et al 2007; Pauers et al 2008;Lehtonen 2014), presumably because males recognize them as more likely to share Difference in intrasexual competition behaviors directed toward red versus black males is given across male color types and sensory environments.…”

“…Increased aggression toward similar males drives frequency-dependent selection, which can promote the invasion of new traits and the coexistence of multiple morphs (Qvarnstrom et al 2012). Agonistic behavior between types, as observed here, however, is instead thought to select for divergence in resource or habitat use (Adams 2004;Peiman and Robinson 2007).…”

The relationship between sexual selection and speciation

“…In an interesting twist to the topic, Qvarnström et al (2012) point out that although current work on sexual selection and speciation almost universally focuses on sexual selection generated by female choice, there are likely to be a number of interesting ways in which male contest competition may promote speciation, including by generating disruptive selection and speeding adaptation in isolated or partially isolated populations. This review provides fodder for a shift to a novel focus in analyses of the ways in which sexual selection and speciation can be related.…”