Temporal genetic stability and high effective population size despite fisheries-induced life-history trait evolution in the North Sea sole

Abstract

Heavy fishing and other anthropogenic influences can have profound impact on a species' resilience to harvesting. Besides the decrease in the census and effective population size, strong declines in mature adults and recruiting individuals may lead to almost irreversible genetic changes in life-history traits. Here, we investigated the evolution of genetic diversity and effective population size in the heavily exploited sole (Solea solea), through the analysis of historical DNA from a collection of 1379 sole otoliths dating back from 1957. Despite documented shifts in life-history traits, neutral genetic diversity inferred from 11 microsatellite markers showed a remarkable stability over a period of 50 years of heavy fishing. Using simulations and corrections for fisheries induced demographic variation, both single-sample estimates and temporal estimates of effective population size (N(e) ) were always higher than 1000, suggesting that despite the severe census size decrease over a 50-year period of harvesting, genetic drift is probably not strong enough to significantly decrease the neutral diversity of this species in the North Sea. However, the inferred ratio of effective population size to the census size (N(e) /N(c) ) appears very small (10(-5) ), suggesting that overall only a low proportion of adults contribute to the next generation. The high N(e) level together with the low N(e) /N(c) ratio is probably caused by a combination of an equalized reproductive output of younger cohorts, a decrease in generation time and a large variance in reproductive success typical for marine species. Because strong evolutionary changes in age and size at first maturation have been observed for sole, changes in adaptive genetic variation should be further monitored to detect the evolutionary consequences of human-induced selection.

Selective exploitation of spatially structured coastal fish populations by recreational anglers may lead to evolutionary downsizing of adults

“…We also provided evidence for limited population connectivity, which likely leads to limited gene flow in S. scriba. Often, the large effective population size of marine fish has been proposed to constitute barriers to fisheriesinduced evolution (Cuveliers et al 2011). We have shown, however, that meta-populations of the small coastal species S. scriba may develop reproductively isolated sub-populations on small spatial scales, which are characterised by high levels of local selfrecruitment and low direct and indirect connectivity with each other.…”

Multi-marker estimate of genetic connectivity of sole (Solea solea) in the North-East Atlantic Ocean

“…This pattern was supported by the strong correlation between geographic and genetic distance based on microsatellite markers and by individual-based cluster analyses identifying two main overlapping population clusters. No evidence for closed populations or genetic patchiness could be observed in the North Sea, indicating a large eVective population size of spawning aggregations (Cuveliers et al 2011) and/or suYcient genetic connectivity between North Sea populations.…”

“…Weak population structure may result from the recent colonization histories following postglacial sea level rise and high eVective population size (N e ), reducing the eVects of genetic drift detected by microsatellite markers. For sole in the North Sea, eVective population size estimates based on the analysis of archived otolith samples with microsatellite markers were large (Cuveliers et al 2011). Therefore, low F ST values do not necessarily imply high gene Xow (Hedgecock et al 2007;Larmuseau et al 2010a;Whitlock and McCauley 1999), but could be due to the long time span needed before F ST reaches equilibrium.…”

Evolution of Marine Organisms under Climate Change at Different Levels of Biological Organisation

“…For example, populations in isolated environments, such as the Baltic Sea, may also undergo isolation and develop genetic endemism as a result of local extinctions or adaptation by evolutionary rescue [104]. Therefore, population size and genetic variation in the context of the intensity and duration of environmental selection pressures must be considered [105] to identify what part of the population (i.e., the effective population size [106]) contributes to the next generation. Populations may have an increased chance of persistence if they react to changing climatic conditions with higher phenotypic plasticity.…”