THE EFFECT OF A VARIABLE ENVIRONMENT ON THE GENETIC CORRELATION STRUCTURE IN A FIELD CRICKET

The evolutionary trajectory of a trait depends not only on the presenc e of genetic variation, but also on the pattern of genetic correlation s (r(g)) among traits. Genetic correlations are most easily measured u nder homogeneous, controlled laboratory conditions, whereas natural po pulations typically experience a higher degree of environmental variab ility. The effect of environmental variability on genetic correlations in the cricket, Gryllus pennsylvanicus, was studied by measuring gene tic correlations within and between two environments differing in leve ls of environmental heterogeneity. Within-environment r(g) among morph ological traits measured in the homogeneous laboratory environment wer e found to be reliable predictors of r(g) measured in the experimental field environment. Laboratory measures of r(g) involving life-history traits, though, were not found to reflect the same correlations measu red in the heterogeneous environment. A significant negative genetic c orrelation between fecundity and developmental time was found in the f ield environment, yet was not detectable when measured in the laborato ry. Phenotypic correlations may be obtained much more easily than gene tic correlations, but their usefulness in evolutionary inference depen ds on the pattern of similarity between the two correlations. A compar ison of genetic and phenotypic correlations revealed a close match bet ween the two measures for morphological traits, but revealed only broa d similarities when considering life-history traits. Male-female genet ic correlations between morphological traits were high (all r(g) > 0.7 3) and were consistently higher in the field environment than in the l aboratory. The genetic correlations between the sexes in developmental time followed the same trend, but the male-female genetic correlation of gonad weights was low in both environments. Across-environment cor relations were found to be strong for morphological traits and for gon ad weight, whereas the genetic expression of developmental time was fo und to be dependent on the environment in which the crickets were rais ed.