The evolutionary legacy of size‐selective harvesting extends from genes to populations

Abstract

Size-selective harvesting is assumed to alter life histories of exploited fish populations, thereby negatively affecting population productivity, recovery, and yield. However, demonstrating that fisheries-induced phenotypic changes in the wild are at least partly genetically determined has proved notoriously difficult. Moreover, the population-level consequences of fisheries-induced evolution are still being controversially discussed. Using an experimental approach, we found that five generations of size-selective harvesting altered the life histories and behavior, but not the metabolic rate, of wild-origin zebrafish (Danio rerio). Fish adapted to high positively size selective fishing pressure invested more in reproduction, reached a smaller adult body size, and were less explorative and bold. Phenotypic changes seemed subtle but were accompanied by genetic changes in functional loci. Thus, our results provided unambiguous evidence for rapid, harvest-induced phenotypic and evolutionary change when harvesting is intensive and size selective. According to a life-history model, the observed life-history changes elevated population growth rate in harvested conditions, but slowed population recovery under a simulated moratorium. Hence, the evolutionary legacy of size-selective harvesting includes populations that are productive under exploited conditions, but selectively disadvantaged to cope with natural selection pressures that often favor large body size.

Evolution of boldness and life history in response to selective harvesting

“…Therefore, 616 evolutionary costs while considering behavior with respect to size are smaller from an adult size (and likely yield) perspective than assumed before in life-history models that 618 omit behavioral dynamics. Importantly, a recent experimental harvesting experiment in zebrafish (Danio rerio) that strongly selected on size found evolution of timidity and at 620 the same time only subtle changes in terminal size and no evolution of juvenile growth rate (Uusi-Heikkilä et al 2015), agreeing with our findings. 622…”

“…These results are well-known from life-history theory (Stearns 1992), evolutionary fisheries models of various structure (Arlinghaus et al 542 2009;Poos et al 2011;Dunlop et al 2015a), laboratory experiments with model fish species (Uusi-Heikkilä et al 2015) and from time-series analysis of phenotypic field data 544 of harvested natural populations (Jørgensen et al 2007;Devine et al 2012;Heino et al 2015). We demonstrate that selection on boldness can have strong additional impacts 546 on growth rate and asymptotic size.…”

Altered trait variability in response to size-selective mortality

“…We used wild-collected zebrafish and reared individuals in each generation in identical environmental and density conditions in the laboratory [7]. The three experimental populations originally consisted of 450 individuals per two replicated tanks.…”

The life aquatic: advances in marine vertebrate genomics

“…Extensive phenotypic studies have suggested that such fisheries-induced evolution is widespread among the world's fish stocks 78,79 , but the extent to which the observed changes truly are genetic and occur over timescales that are relevant for fisheries managers remains controversial 80,81 . Recent experimental studies have started to identify specific genomic regions associated with fisheries-induced evolution and have found evidence for selection effects on genes previously linked to body size variation 82 , embryological metabolism, stress response and immune function 83 . Moreover, heritable changes in the expression of hundreds of genes can happen in a generation 84 .…”