Is Sexual Conflict an "Engine of Speciation"?

Abstract

At the end of the last century, sexual conflict was identified as a powerful engine of speciation, potentially even more important than ecological selection. Earlier work that followed-experimental, comparative, and mathematical-provided strong initial support for this assertion. However, as the field matures, both the power of sexual conflict and constraints on the evolution of reproductive isolation as driven by sexual conflict are becoming better understood. From theoretical studies, we now know that speciation is only one of several possible evolutionary outcomes of sexual conflict. In line with these predictions, both experimental evolution studies and comparative analyses of fertilization proteins and of species richness show that sexual conflict leads to, or is associated with, reproductive isolation and speciation in some cases but not in others. Increased genetic variation (especially in females) without reproductive isolation is an underappreciated consequence of sexually antagonistic selection. By the end of 1990s, studies of sexual conflict and sexually antagonistic coevolution moved to the forefront of experimental and theoretical research in evolutionary biology (Rice and Holland 1997;Holland and Rice 1998;Rice 1998). Although the potential evolutionary importance of sexual conflict was anticipated and articulated from a theoretical point of view by Geoff Parker 20 years earlier (Parker 1979), the explosive interest in this topic was a result of groundbreaking experimental work with Drosophila melanogaster by Bill Rice (1993Rice ( , 1996, which directly showed high potential for sexually antagonistic coevolution.Sexual conflict is a special case of intragenomic conflict (Rice and Holland 1997;Rice 1998;Crespi and Nosil 2013). Sexual conflict occurs if the interests of the sexes with regard to certain aspects of reproduction differ (Parker 1979;Arnqvist and Rowe 2005). Ultimately, sexual conflict arises because of the differences in the roles played by the sexes in the process of reproduction, which in turn lead to the differences between the sexes in the costs and benefits of mating and reproduction (Bateman 1948;Trivers 1972;Parker 1979). Sexual conflict can occur over mating rate (Rice and Holland 1997;Holland and Rice 1998;Rice 1998) ker and Partridge 1998). Within-locus conflict occurs when the locus controls a trait expressed in both sexes and the optimum trait values differ between the sexes. As a result, optimizing the trait value in one sex will lead to a fitness reduction in the other sex. Within-locus conflict can be resolved via a number of mechanisms, including the evolution of sex linkage, sex-specific expression of genes, gene duplication, and condition dependence (Bonduriansky and Chenoweth 2009;van Doorn 2009). Between-locus conflict occurs when there are two different (sets of ) traits each expressed in one sex only but affecting the fitness of both sexes in opposite directions. In this case, adaptive changes in a trait of one sex cause deleterious fitness consequences for the othe...

Contrasting effects of intralocus sexual conflict on sexually antagonistic coevolution

“…This disparity has the potential to ignite two forms of sexual conflict (5): interlocus and intralocus sexual conflict (IRSC and IASC, respectively). Both forms of conflict have been described as independent drivers of divergence and speciation (5)(6)(7)(8) and have important implications for the rate of trait evolution, the maintenance of genetic variation, and sexual selection (9)(10)(11)(12).…”

A rigorous comparison of sexual selection indexes via simulations of diverse mating systems

“…O ur understanding of sexual selection is obstructed by lack of progress on a fundamental question: How do we measure sexual selection rigorously, and how do we compare its strength between the sexes or across taxa (1-3)? Sexual selection underlies some of the most extreme traits in nature, including spectacular armaments and ornaments, and affects macroevolution via both speciation and extinction (4)(5)(6)(7)(8). It is thought to vary systematically with a species' mating system (i.e., the degree of multiple mating by each sex) and with sex-specific investment in offspring and mating partners (i.e., parental investment and direct benefits) (9,10).…”

Transcriptome, genetic editing, and microRNA divergence substantiate sympatric speciation of blind mole rat, Spalax

“…However, whether all these criteria could be detected in all of the emergent SS cases is still unclear. Rising empirical (5) (SI Appendix, Suggested Reading) and theoretical studies (6,7) demonstrated that SS may be common in nature, although it is still being highly debated (4). Recently, we demonstrated SS in the blind mole rat, Spalax galili, by both mitochondrial genome (8) and by whole-genome resequencing (5), demonstrating divergence across the whole genome with ongoing gene flow.…”