1. ¹Department of Population Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-75236 Uppsala, Sweden
2. ²Ecological Genetics Research Unit, Department of Ecology and Systematics, PO Box 65, FIN-00014 University of Helsinki, Finland
3. ³Rolf Nevanlinna Institute, PO Box 4, FIN-00014 University of Helsinki, Finland

Correspondence: J Merilä, Ecological Genetics Research Unit, Department of Ecology and Systematics, PO Box 65, FIN-00014 University of Helsinki, Finland. E-mail: juha.merila@helsinki.fi

Received 29 July 2002; Accepted 11 February 2003.

Abstract

The influence of environmental stress on the expression of genetic and maternal effects on the viability traits has seldom been assessed in wild vertebrates. We have estimated genetic and maternal effects on the viability (viz probability of survival, probability of being deformed, and body size and shape) of common frog, Rana temporaria, tadpoles under stressful (low pH) and nonstressful (neutral pH) environmental conditions. A Bayesian analysis using generalized linear mixed models was applied to data from a factorial laboratory experiment. The expression of additive genetic variance was independent of pH treatments, and all traits were significantly heritable (survival: h²0.08; deformities: h²0.26; body size: h²0.12; body shape: h²0.14). Likewise, nonadditive genetic contributions to variation in all traits were significant, independent of pH treatments and typically of magnitude similar to the additive genetic effects. Maternal effects were large for all traits, especially for viability itself, and their expression was partly dependent on the environment. In the case of body size, the maternal effects were mediated largely through egg size. In general, the results give little evidence for the conjecture that environmental stress created by low pH would impact strongly on the genetic architecture of fitness-related traits in frogs, and hamper adaptation to stress caused by acidification. The low heritabilities and high dominance contributions conform to the pattern typical for traits subject to relatively strong directional selection.