Fisheries-induced evolution of neutral and selected genetic markers
According to life-history theory, the strong and size-selective mortalities imposed by modern fishing are supposed to induce evolution in life-history traits such as growth, age and size at maturation, and reproductive investment. In accordance with this expectation, many field studies have revealed altered growth rates, earlier maturation at smaller size, and higher reproductive effort in harvested populations.
Experiments have corroborated these results, showing that surprisingly rapid adaptive evolution is possible in response to harvesting. Unfortunately, genes coding for detailed aspects of fish life histories have not been identified so far, which precludes validating the genetic nature of observed phenotypic trends. Genetic analyses of fish stocks have instead focused on neutral genetic markers such as microsatellites. This allowed studying the neutral evolution of genetic diversity, which has been shown to decline in some harvested populations. Life-history traits and neutral genetic markers are indeed subject to neutral evolution through genetic drift, i.e., through purely random processes affecting allele frequencies that are the more pronounced the smaller a population’s size.
The aim of this project is to develop a generic model for studying the interplay between neutral and adaptive evolution in the context of fishing. For this purpose, an individual-based model will be devised that includes neutral genetic markers as well as quantitative life-history traits, and that accounts for the complex ecology of exploited fish stocks. Our model analyses are planned to address three objectives. First, we will explore whether we can identify relationships between fisheries-induced changes in the distributions of neutral genetic markers and changes in demographic stock characteristics such as population size, spawning stock biomass, and recruitment.
Second, we will analyze the relative contribution of genetic drift and adaptive evolution in the responses of life-history traits to fishing. Third, we will investigate potential patterns linking neutral and adaptive genetic changes. If such a correlation were found, neutral markers, which are much easier to analyse empirically, could be used to establish early-warning signals for fisheries-induced evolutionary changes in exploited stocks.