| Summary: | How population size influences quantitative genetic variation and differentiation among natural, fragmented populations remains unresolved. Small, isolated populations might occupy poor quality habitats and lose genetic variation more rapidly due to genetic drift than large populations. Genetic drift might furthermore overcome selection as population size decreases. Collectively, this might result in directional changes in additive genetic variation (VA) and trait differentiation (QST) from small to large population size. Alternatively, small populations might exhibit larger variation in VA and QST if habitat fragmentation increases variability in habitat types. We explored these alternatives by investigating VA and QST using nine fragmented populations of brook trout varying 50-fold in census size N (179-8416) and 10-fold in effective number of breeders, Nb (18-135). Across 15 traits, no evidence was found for consistent differences in VA and QST with population size and almost no evidence for increased variability of VA or QST estimates at small population size. This suggests that (i) small populations of some species may retain adaptive potential according to commonly adopted quantitative genetic measures and (ii) populations of varying sizes experience a variety of environmental conditions in nature, however extremely large studies are likely required before any firm conclusions can be made. Trait measurements and pedigrees for Cape Race brook trout populationsIndividual trait measurements and pedigrees used in animal models to estimate quantitative genetic parameters for fifteen traits for nine brook trout populations from Cape Race, Newfoundland, Canada.CR_traits_pedigrees.xlsxCape Race breeding design summaryA table summarizing, per population, the number of females and males used to generate families as well as the range and mean number of crosses per male for the common garden experiment used to estimate quantitative genetic parameters for Cape Race brook trout ...
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