Lifetime reproductive success and heritability in nature

The observation that traits closely related to fitness ("fitness traits") h ave lower heritabilities than traits more distantly associated with fitness has traditionally been framed in terms of Fisher's fundamental theorem of natural selection-fitness traits are expected to have low levels of additiv e genetic variance due to rapid fixation of alleles conferring highest fitn ess. Subsequent treatments have challenged this view by pointing out that h igh environmental and non-additive genetic contributions to phenotypic vari ation may also explain the low heritability of fitness trails. Analysis of a large data set from the collared flycatcher Ficedula albicollis confirmed a previous finding that traits closely associated with fitness tend to hav e lower heritability. However, analysis of coefficients of additive genetic variation (CVA) revealed that traits closely associated with fitness had h igher levels of additive genetic variation (V-A) than traits more distantly associated with fitness. Hence, the negative relationship between a trait' s association with fitness and its heritability was not due to lower levels of V-A in fitness traits but was due to their higher residual variance. Ho wever, whether the high residual variance was mainly due to higher levels o f environmental variance or due to higher levels of nonadditive generic var iance remains a challenge to be addressed by further studies. Our results a re consistent with earlier suggestions that fitness-related traits may have more complex genetic architecture than traits more distantly associated wi th fitness.