Heritability and ‘evolvability’ of fitness components in Callosobruchus maculatus

Abstract

Heritabilities of traits closely related to fitness (e.g. life-history traits) tend to be lower than those of morphological traits in natural populations. It is unclear, however, whether this pattern reflects relatively low additive-genetic variation, relatively high residual variation (i.e. non-additive and environmental effects) or both. A standard, half-sib breeding design was used to estimate narrow-sense heritabilities and coefficients of additive-genetic variation (CV_A) for a life-history trait (total fecundity), a morphological trait (wing length) and a behavioural trait (allocation of eggs among available resources) in two outbred populations of the seed beetle Callosobruchus maculatus. Heritabilities of fecundity and wing length were high in both populations whereas the heritability of egg-laying behaviour was low but non-zero. In contrast, estimates of ‘evolvability’, which depend on CV_A, were highest for fecundity, intermediate for egg-laying behaviour and lowest for wing length. These results resemble those from a recent survey of Drosophila studies and suggest that the typically low heritabilities of behavioural or life-history traits are better explained by high residual variation than by low additive-genetic variation. Phenotypic and genetic correlations were generally not significant except for a positive relationship between wing length and fecundity. No evidence was obtained of a trade-off or underlying functional relationship between the number of eggs laid and the pattern of egg dispersion among available resources.