Size-selective harvesting fosters adaptations in mating behavior and reproductive allocation, affecting sexual selection in fish

1. The role of sexual selection in the context of harvest-induced evolution is poorly understood. However, elevated and trait-selective harvesting of wild populations may change sexually-selected traits, which in turn can affect mate choice and reproduction.
2. We experimentally evaluated the potential for fisheries-induced evolution of mating behavior and reproductive allocation in fish.
3. We used a unique experimental system of zebrafish (Danio rerio) lines exposed to large, small, or random (i.e. control) size-selective mortality. The large-harvested line represented a treatment simulating the typical case in fisheries where the largest individuals are preferentially harvested. We used a full factorial design of spawning trials with size-matched individuals to control for the systematic impact of body size during reproduction, thereby singling out possible changes in mating behaviour and reproductive allocation.
4. Both small and large size-selective mortality left a legacy on male mating behavior by elevating intersexual aggression. However, there was no evidence for line-assortative reproductive allocation. Females of all lines preferentially allocated eggs to the generally less aggressive males of the random-harvested control line. Females of the large-harvested line showed enhanced reproductive performance, and males of the large-harvested line had the highest egg fertilization rate among all males. These findings can be explained as an evolutionary adaptation by which individuals of the large-harvested line display an enhanced reproductive performance early in life to offset the increased probability of adult mortality due to harvest.
5. Our results suggest that the large-harvested line evolved behaviorally-mediated reproductive adaptations that could increase the rate of recovery when populations adapted to high fishing pressure come into secondary contact with other populations.