Male-benefit adaptation under sex-limited selection shaped by compensatory evolution in Drosophila melanogaster.

Abstract

Intralocus sexual conflict (IaSC) results from opposing selection acting on traits with correlated expression between the sexes. We recently reported on a male-limited (ML) selection experiment in Drosophila melanogaster designed to investigate IaSC through a sex-limited evolution regime that theoretically resolves conflict in favour of males. However, this experiment did not universally or unambiguously improve male fitness, although female fitness declined as predicted. Here we examine sources of unintended selection: unusual genetic features of the breeding design and the special females used to enforce male-limited inheritance that may have complicated evolutionary outcomes. Specifically, we evaluate the effects of a foreign cytoplasm, genetically marked translocated autosomes, and a female-exposed Y chromosome derived from the clone-generator (CG) system, and the unique environment of sexual selection introduced by foreign CG females. We found that selected male fitness increased by 66% when expressed within the full ML genetic context, rising to over 100% when interacting with CG females. While there is no consistent fitness advantage in the "wild type" genetic background, there is a nearly significant trend of improved fitness with CG females (26% improvement). Further, outside this context, these males do not experience a fitness loss relative to controls, even showing a marginal gain of 6%. Uniformly, these gains were mediated by precopulatory traits: ML selection produced more attractive males with greater mating success and shorter mating latencies, while sperm competition remained unchanged. Intriguingly, ML-evolved males also exhibited reduced mate harm to females, contrary to the established narrative of escalating intersexual antagonism in this system. Dissecting individual components revealed significant fitness improvements associated with adaptation to the foreign cytotype (18%) and the female-exposed Y chromosome (33%), although responses varied across replicate populations. Moreover, when selected haplotypes were expressed together with the foreign cytotype in females, we observe a recovery in fitness. Together, these findings demonstrate extensive compensatory evolution to the ML selection environment, indicating that responses to the release of IaSC were shaped not only by sexually antagonistic selection but also by adaptation to the genetic manipulations and mating context inherent to the experimental design.