Sexual conflict over mating in lygaeus seed bugs

Abstract

Sexual conflict has been proposed to be important for evolution, and is often implicated in population divergence and speciation through sexually antagonistic co-evolution (SAC). However, empirical tests of these ideas on field populations are few. How sexual conflict, and SAC, operates in the wild, remains an important unanswered question if we are to fully understand the role of sexual conflict in evolution in nature. Here, I studied sexual conflict over mating in the seed feeding bugs Lygaeus equestris and Lygaeus simulans. Firstly, I show that laboratory adapted populations of L. equestris that differ in the magnitude of sexual conflict also differ in aspects of their reproductive development and mating propensity, with the population displaying greater conflict load also mating more readily. Study of female receptivity to mating as an evolvable trait, that could be involved in conflict over mating, revealed moderate to low heritability at two age groups. To better understand variation in the expression of sexual conflict in the wild, field caught populations of L. equestris, ranging across its distribution, and also of its sister species, L. simulans, were assayed for the magnitude of sexual conflict over mating in common garden laboratory experiments. High female mating costs were apparent across the populations, but the magnitude of these costs did not vary. No consistent patterns of mating costs and life history variation were found however, arguing against close links between mating costs and life-history. Finally, I investigated whether populations displaying sexual conflict over mating have begun to diverge, and evolve reproductive isolation. I found no evidence of reproductive isolation, or variation in mating propensity, between populations of L. equestris when crossed in reciprocal no-choice mating trials. However, L. equestris and L. simulans did show pre-zygotic reproductive isolation albeit with asymmetries between the reciprocal crosses (L. simulans males were able to mate L. equestris females, but male L. equestris were largely unable to mate L. simulans females). As expected for close taxa that perhaps have not been diverged for long, pre-zygotic isolation was perhaps stronger than post-zygotic isolation, as F2 offspring were generated by some of the inter-specific crosses: gene flow can therefore occur between these species contrary to previous studies. My data suggest that sexual conflict over mating may reduce the likelihood of speciation through the evolution of male persistence, as well as promote it through population divergence.