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

Abstract

The presence of heritable variation in traits is a prerequisite for evolution. The great majority of heritability (h2 ) estimates are performed 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 quantitative variation, although theoretical extrapolations from lab studies have been attempted. Here we investigate the effects of environmental heterogeneity on variance component estimation using full-sib families of Gryllus pennsylvanicus split between a homogeneous laboratory environment and a more variable field environment. Although large standard errors prevent demonstration of statistically significant differences among h2 of traits measured in the two environments for all but one trait, the values of h2 are, on average, lower in the variable field environment, with a mean reduction of 19%. Developmental time is an exception, exhibiting high levels of additive variance in the field, leading to a higher value of h2 in the variable environment. Underlying the lower field h2 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 environmental component of variance in the field is any more important in the reduction of h2 than is the decrease in the additive genetic component. The implications of the relative changes in the two components of variance are discussed.