The quantitative genetics of physiological and morphological traits in an invasive terrestrial snail: additive vs. non‐additive genetic variation

The distribution of additive vs. non-additive genetic variation in natural populations represents a central topic of research in evolutionary/organismal biology. For evolutionary physiologists, functional or whole-animal performance traits ('physiological traits') are frequently studied assuming they are heritable and variable in populations. Physiological traits of evolutionary relevance are those functional capacities measured at the whole-organism level, with a potential impact on fitness. They can be classified as capacities (or performances) or costs, the former being directly correlated with fitness and the latter being inversely correlated with fitness (usually assumed as constraints). In spite of their obvious adaptive significance, the additive genetic variation in physiological traits, and its relative contribution to phenotypic variance (or narrow-sense heritability) in comparison with maternal, dominance or epistatic variance, is known only for a few groups such as insects and mammals. In this study, we assessed the additive and maternal/non-additive genetic variation in a suite of physiological and morphological traits in populations of the land snail Cornu aspersum. Except for dehydration rate (h(2)=0 center dot 32 +/- 0 center dot 15), egg mass (h(2)=0 center dot 82 +/- 0 center dot 30) and hatchling mass (h(2)=1 center dot 01 +/- 0 center dot 31; population=fixed effect), we found very low additive genetic variation. Large non-additive/maternal effects were found in all traits. Cage effects did not change the results, indicating low contribution of common environmental variance to our results. No differences were found between the phenotypic and non-additive genetic variance/covariance matrices. Even though we compared populations across 1300km in a common garden set-up, our results suggest an absence of physiological as well as morphological differentiation in these populations. These results contrast with previous analyses in the original distributional range of this species, which found high additive genetic variation in morphological traits. These are intriguing results demanding further quantitative genetic studies in the original distributional range of this species as well as the history of colonization of this invasive species.