Abstract
Male reproductive phenotypes can evolve in response to the social and sexual environment. The expression of many such phenotypes may also be plastic within an individual's lifetime. For example, male Drosophila melanogaster show significantly extended mating duration following a period of exposure to conspecific male rivals. The costs and benefits of reproductive investment, and plasticity itself, can be shaped by the prevailing sociosexual environment and by resource availability. We investigated these ideas using experimental evolution lines of D. melanogaster evolving under three fixed sex ratios (high, medium, and low male-male competition) on either rich or poor adult diets. We found that males evolving in high-competition environments evolved longer mating durations overall. In addition, these males expressed a novel type of plastic behavioral response following exposure to rival males: they both significantly reduced and showed altered courtship delivery, and exhibited significantly longer mating latencies. Plasticity in male mating duration in response to rivals was maintained in all of the lines, suggesting that the costs of plasticity were minimal. None of the evolutionary responses tested were consistently affected by dietary resource regimes. Collectively, the results show that fixed behavioral changes and new augmentations to the repertoire of reproductive behaviors can evolve rapidly.
Highlights
Male reproductive investment is shaped by the level of pre- and post-mating sexual competition in many species
That male mating behaviour would evolve in response to the level of male-male competition imposed by the fixed sex ratio regimes, was supported
The pattern was repeatable across experiments 1-3 (Figure 1, S1; Table S1b-S1d). This supported the prediction that sex ratio imposed directional selection on overall mating duration, leading to extended mating duration among MB males in response to the consistently high level of competition exerted in the male-biased regimes
Summary
Male reproductive investment is shaped by the level of pre- and post-mating sexual competition in many species. We studied plastic male mating duration and latency among males evolved under both fixed sex ratio and either rich or poor adult diet regimes, to test the effects of, and interactions between, the social environment and resource limitation on male reproductive investment and plasticity.
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