Local adaptation and genetics of acid-stress tolerance in the moor frog, Rana arvalis

As potential to adapt to environmental stress can be essential for population persistence, knowledge on the genetic architecture of local adaptation is important for conservation genetics. We investigated the relative importance of additive genetic, dominance and maternal effects contributions to acid stress tolerance in two moor frog (Rana arvalis) populations originating from low and neutral pH habitats. Experiments with crosses obtained from artificial matings revealed that embryos from the acid origin population were more tolerant to low pH than embryos from the neutral origin population in embryonic survival rates, but not in terms of developmental stability, developmental and growth rates. Strong maternal effect and small additive genetic contributions to variation were detected in all traits in both populations. In general, dominance contributions to variance in different traits were of similar magnitude to the additive genetic effects, but dominance effects outweighed the additive genetic and maternal effects contributions to early growth in both populations. Furthermore, the expression of additive genetic variance was independent of pH treatment, suggesting little additive genetic variation in acid stress tolerance. The results suggest that although local genetic adaptation to acid stress has taken place, the current variation in acid stress tolerance in acidified populations may owe largely to non-genetic effects. However, low but significant heritabilities ( h(2) approximate to 0.07 - 0.22) in all traits - including viability itself - under a wide range of pH conditions suggests that environmental stress created by low pH is unlikely to lower moor frog populations' ability to respond to selection in the traits studied. Nevertheless, acid conditions could lower populations' ability to respond to selection in the long run through reduction in effective population size.