The effect of environmental variability on heritabilities and genetic correlations of traits in the field cricket, Gryllus pennsylvanicus /

The amount of heritable variation and the pattern of genetic covariation in traits are the chief determinants in the evolution of a population, at least over the short term. A preponderance of heritability (h$ sp2)$ and genetic (r$ rm sb g)$ experiments are performed under laboratory conditions which are characterized by low levels of environmental variability. This thesis describes the investigation of the effects of environmental heterogeneity on phenotypic components of variance and covariance. Full-sib families of the field cricket, Gryllus pennsylvanicus, were split between a homogeneous laboratory environment and a more variable field environment. The values of h$ sp2$ were, on average, lower in the variable field environment, with a mean reduction of 19%. Development time was an exception, exhibiting high levels of additive variance in the field. Substantial decreases in generic components of variance contributed to the lower field h$ sp2$ estimates, as well as the expected increases in the components of environmental variance. Within-environment r$ rm sb g$ among morphological traits were not found to differ between the two environments. Laboratory measures of r$ rm sb g$ involving life history traits, though, were not found to reflect the same correlations measured in the heterogeneous environment. A significant negative genetic correlation between fecundity and development time was found in the field environment, yet was not observed in the laboratory. Male-female genetic correlations between morphological traits were high (all r$ rm sb g>0.73),$ and were consistently higher in the field environment than in the laboratory. The genetic correlations between the sexes in development time followed the same trend, but gonad weight showed no similarity between the sexes in either environment. Across-environment correlations within each trait are also discussed