The quantitative genetic basis of adaptive divergence in the moor frog (Rana arvalis) and its implications for gene flow

Knowledge on the relative contribution of direct genetic, maternal and environmental effects to adaptive divergence is important for understanding the drivers of biological diversification. The moor frog (Rana arvalis) shows adaptive divergence in embryonic and larval fitness traits along an acidification gradient in south-western Sweden. To understand the quantitative genetic basis of this divergence, we performed reciprocal crosses between three divergent population pairs and reared embryos and larvae at acid and neutral pH in the laboratory. Divergence in embryonic acid tolerance (survival) was mainly determined by maternal effects, whereas the relative contributions of maternal, additive and nonadditive genetic effects in larval life-history traits differed between traits, population pairs and rearing environments. These results emphasize the need to investigate the quantitative genetic basis of adaptive divergence in multiple populations and traits, as well as different environments. We discuss the implications of our findings for maintenance of local adaptation in the context of migrant and hybrid fitness.