ABSTRACT
Rapid life-history changes caused by size-selective harvesting are often interpreted as a response to direct harvest selection against a large body size. However, similar trait changes may result from a harvest-induced relaxation of natural selection for a large body size via density-dependent selection. Here, we show evidence of such density-dependent selection favouring large-bodied individuals at high population densities, in replicated pond populations of medaka fish. Harvesting, in contrast, selected medaka directly against large-bodied medaka and, in parallel, decreased medaka population densities. Five years of harvesting were enough for harvested and unharvested medaka populations to inherit the classically-predicted trait differences, whereby harvested medaka grew slower and matured earlier than unharvested medaka. We demonstrate that this life-history divergence was not driven by direct harvest selection for a smaller body size in harvested populations, but by density-dependent natural selection for a larger body size in unharvested populations.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Statement of authorship: ABH performed the laboratory F1 experiment, contributed to data analysis, wrote the first draft of the manuscript and contributed to subsequent versions. EE designed the study, contributed to the pond experiment, performed data analysis, and led manuscript writing from the second version. JM, DC, SA, AM, SP, EM and BD contributed to both the pond and laboratory experiments.
Data accessibility statement: Should the manuscript be accepted, the data supporting the results will be archived in an appropriate public repository and the data DOI will be included at the end of the article.
