Abstract
The effective size of a population (Ne) determines the retention of neutral genetic variation in isolated populations, and is therefore a key parameter in conservation genetics. However, while our knowledge on the genetic properties of endangered populations has vastly improved in recent decades, rather little is known about the drivers of variation in Ne/Nc (the ratio between Ne and the population census size Nc) within given species. In the present study, we used eight microsatellite markers to genotype 898 adult common toads (Bufo bufo) obtained over five reproductive seasons from a single population (2004–2006 and 2008–2009), and related annual measures of Ne to cohort-specific population attributes. Consistent with the hypothesis that shifts in fitness-related traits can alter reproductive shares, we observed an increase in annual Ne and Ne/Nc ratios in parallel with a decline in body size in both sexes, and in parallel with an increase in body condition in males. The obtained Ne values also corresponded well with parentage inferences across the 6-year study period, which assigned 46.3% of individuals recorded in 2008 and 2009 to at least one putative parent from the 2004–2006 cohorts. Our study highlights a possible causative link between phenotypic traits such as body size and Ne/Nc, which has the potential to influence the amount of genetic erosion through drift.
Highlights
The effective size of a population (Ne) is the main determinant of the standing amount of genetic variation in isolated demes, and a central concept in conservation biology (e.g. Charlesworth 2009)
Of particular note is the regular observation that Ne/Nc is higher in rather small populations, resulting in a lower relative rate of genetic erosion in demes comprising small numbers of individuals (“genetic compensation”, Ardren and Kapuscinski 2003; Jehle et al 2005; Beebee 2009; Bernos and Frazer 2016; Ferchaud et al 2016; but see Mueller et al 2016 who report on a case of Ne/Nc rising with Nc due to increased adult survival)
To shed more light into mechanisms which govern the retention of genetic variation in endangered populations, there is currently a need to relate Ne to population traits across a wider range of taxa and environments
Summary
The effective size of a population (Ne) is the main determinant of the standing amount of genetic variation in isolated demes, and a central concept in conservation biology (e.g. Charlesworth 2009). Of particular note is the regular observation that Ne/Nc is higher in rather small populations (i.e., there is an inverse relationship between Ne/Nc and Nc), resulting in a lower relative rate of genetic erosion in demes comprising small numbers of individuals (“genetic compensation”, Ardren and Kapuscinski 2003; Jehle et al 2005; Beebee 2009; Bernos and Frazer 2016; Ferchaud et al 2016; but see Mueller et al 2016 who report on a case of Ne/Nc rising with Nc due to increased adult survival). Reproductive contributions heavily depend on fitness-related traits such as body size, studies which link Ne/Nc ratios with phenotypic attributes are so far largely lacking
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