![]() ![]() Previous modeling studies ( 24, 25) highlighted the importance of considering the contribution of population density in harvest-induced evolution, but, so far, empirical studies examining how population density reduction can affect selection and evolutionary potential in a fisheries context are lacking. Different phenotypes and genotypes may therefore be selected by fishing pressures depending on population density, creating G×E effects to produce new selective landscapes and evolutionary trajectories for the remaining population. ![]() Such conditions may not only modify the average phenotype of the remaining population and reduce phenotypic variation within the population ( 23) because of more homogenous food allocation among individuals, but also affect which individuals have a selective advantage in that new context. A reduced population density may then decrease interindividual competition and correspondingly increase resource availability or alter among-individual variation in resource acquisition ( 22). Indeed, intense harvesting can remove so much biomass from the environment that the density for the remaining population is altered. Harvest-associated plasticity could also occur in response to environmental effects because fishing causes other confounding environmental changes that could influence phenotypic expression ( 9, 21), such as the reduction of population density over time. Such genomic information is potentially valuable for predicting the consequences of selective harvest on targeted populations with the benefit of understanding which molecular changes might be involved and fuel evolution. While an analysis of wild populations would require more detailed time series and genomic data to securely infer the genomic responses to fishing ( 11), previous experimental work has mainly examined responses to size-based selection with no attempt to determine whether vulnerability to capture as an integrated trait can indeed select on specific genotypes and underlying genomic variants. Recent research suggests that fisheries can induce a shift in the genomic variants of targeted populations ( 18– 20). If the traits under fishing selection possess a genetic basis, fishing could lead to direct evolution ( 8, 17). ![]() This is especially likely given that commercial fishing methods such as trawling directly exploit aspects of fish foraging, schooling, and escape behaviors to facilitate capture ( 14). While size and maturation are well established to be selected by fishing ( 12, 13), emerging evidence shows that fishing may also drive selection on traits related to bioenergetics or social behavior that also vary widely within species ( 14– 16). Vulnerability is likely comprised of a suite of life history, morphological, physiological, and behavioral traits that interact to determine whether a fish will ultimately escape or be captured by a fishing gear. These results highlight the need to consider environmental factors when predicting effects of human-induced selection and evolution.įor selection by fishing to occur, there must be phenotypic variation among individuals with respect to their vulnerability to capture. The evolutionary consequences of fishing are therefore likely context dependent, possibly varying as exploited populations decline. This interaction between direct fishing selection and density could fundamentally alter the genomic responses to harvest. However, the specific genes under selection-mainly related to brain function and neurogenesis-varied with the population density. ![]() Using experimental fish reared at two densities and repeatedly harvested by simulated trawling, we show consistent phenotypic selection on growth, metabolism, and social behavior regardless of density. Crucially, we lack knowledge of how capture-associated selection and its interaction with reductions in population density caused by fishing can potentially shift which genes are under selection. Fisheries induce one of the strongest anthropogenic selective pressures on natural populations, but the genetic effects of fishing remain unclear. ![]()
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