Data from: Increased male investment in sperm competition results in offspring of lower quality
Male animals often show higher mutation rates than their female conspecifics. A hypothesis for this male-bias is that competition over fertilization of female gametes leads to sexual selection for increased male germline replication at the expense of maintenance and repair, resulting in a trade-off between male success in sperm competition and offspring quality. Here we test this hypothesis using experimental evolution lines of the seed beetle Callosobruchus maculatus, maintained for >50 generations under three alternative mating regimes: natural and sexual selection (N+S-lines), natural selection only (N-lines) or sexual selection only (S-lines). Previous findings suggest that S-males reduce germline maintenance when engaging in reproduction compared to N- and N+S-males. Here, we first show that S-males are superior in sperm competition compared to both N- and N+S-males, suggesting that the removal of trade-offs between naturally and sexually selected male fitness components has resulted in the evolution of increased post-copulatory reproductive success. We then show that S-males produce progeny of lower quality if engaging in socio-sexual interactions with conspecifics prior to being challenged with a dose of irradiation introducing DNA-damage in their germline. We identify 18 candidate genes that showed differential expression in response to the induced germline damage. These genes also showed significant expression changes across socio-sexual treatments of fathers and predicted the reduction in quality of their offspring. Moreover, sex differences in expression of the same 18 genes indicate a substantially higher female investment in germline maintenance. Our findings provide evidence for a trade-off between male success in sperm competition and germline maintenance, suggesting that sex-differences in the relative strengths of sexual and natural selection are causally linked to male-mutation bias.
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