The genetic component of copula duration in the yellow dung fly

Abstract

The heritabilities of copula duration ( h 2=0.39, P<0.01), body size ( h 2=0.76, P<0.001) and development time ( h 2=0.23, P<0.05), plus their genetic covariances, in the yellow dung fly, Scathophaga stercoraria(L.), were assessed using full sibling analysis. The relative order of magnitude of the values agrees with that of other data: morphological>behavioural>life-history characters. Repeated measures of copula duration for each male revealed a general increase in copula duration with Julian date or age. The individual pattern of this change in copula duration (here termed ‘flexibility’), an expression of phenotypic plasticity, was itself marginally heritable ( h 2=0.19, P=0.065). Significant positive phenotypic and genetic covariance was evident only between flexibility of copula duration and body size. All other correlations were not different from zero, including those between development time and body size and between copula duration and body size. It is suggested that in S. stercoraria populations there is some averaging selection towards a mean optimal copula duration which can guide an individual's behaviour in a variety of environments. At the same time, there is selection for phenotypic plasticity which allows individuals to adapt their behaviour to their immediate environment. These effects together are consistent with both the assumptions of optimality models and the classic results on copula duration in yellow dung flies.