Sexual conflict promotes speciation in insects

Abstract

Speciation rates among extant lineages of organisms vary extensively, but our understanding of the causes of this variation and, therefore, the processes of speciation is still remarkably incomplete. Both theoretical and empirical studies have indicated that sexual selection is important in speciation, but earlier discussions have focused almost exclusively on the potential role of female mate choice. Recent findings of postmating reproductive conflicts of interest between the sexes suggest a quite different route to speciation. Such conflicts may lead to perpetual antagonistic coevolution between males and females and may thus generate rapid evolutionary divergence of traits involved in reproduction. Here, we assess this hypothesis by contrasting pairs of related groups of insect species differing in the opportunity for postmating sexual conflict. Groups where females mate with many males exhibited speciation rates four times as high as in related groups where females mate only once. Our results not only highlight the general importance of postmating sexual selection in speciation, but also support the recent suggestion that sexual conflict is a key engine of speciation.

Figure 1

The ratio of species richness in polyandrous clades to that in monandrous clades across the phylogenetic contrasts. Given is mean (±SE) log-transformed relative species richness of the following: 1, all 25 phylogenetic contrasts; 2a, contrasts involving only true sister taxa; 2b, contrasts not involving sister taxa; 3a, contrasts involving within-family comparisons; and 3b, those involving between-family comparisons. Dashed line indicates the null hypothesis of equal number of species in the two types of clades.