THE EFFECT OF ENVIRONMENTAL VARIABILITY ON THE HERITABILITIES OF TRAITS OF A FIELD CRICKET

The presence of heritable variation in traits is a prerequisite for ev olution. The great majority of heritability (h(2)) estimates are perfo rmed under laboratory conditions that are characterized by low levels of environmental variability. Very little is known about the effect of environmental variability on the estimation of components of quantita tive variation, although theoretical extrapolations from lab studies h ave been attempted. Here we investigate the effects of environmental h eterogeneity on variance component estimation using full-sib families of Gryllus pennsylvanicus split between a homogeneous laboratory envir onment and a more variable held environment. Although large standard e rrors prevent demonstration of statistically significant differences a mong h(2) of traits measured in the two environments for all but one t rait, the values of h(2) are, on average, lower in the variable field environment, with a mean reduction of 19%. Developmental time is an ex ception, exhibiting high levels of additive variance in the field, lea ding to a higher value of h(2) in the variable environment. Underlying the lower held h(2) estimates are greater components of environmental variance as expected, as well as lower components of genetic variance . In this study, there is no evidence that the increase in the environ mental component of variance in the held is any more important in the reduction of h(2) than is the decrease in the additive genetic compone nt. The implications of the relative changes in the two components of variance are discussed.