EFFECTS OF TEMPERATURE EXTREMES ON GENETIC VARIANCES FOR LIFE-HISTORYTRAITS IN DROSOPHILA-MELANOGASTER AS DETERMINED FROM PARENT-OFFSPRINGCOMPARISONS

Parent-offspring comparisons were used to investigate the effects of t emperature extremes on genetic variances for two life history traits a nd one morphological trait in Drosophila melanogaster. We considered t hree temperatures (14 degrees C, 25 degrees C and 28 degrees C) for cu lturing and testing flies, and considered heritabilities, coefficients of additive variation (CVA) and evolvabilities (I-A) for fecundity, d evelopment time and wing length. For fecundity, heritabilities and evo lvabilities were higher when parents were exposed to 14 degrees C comp ared to 28 degrees C. Parent-offspring comparisons suggested that gene tic correlations among environments were close to 1, although lower co rrelations were obtained in comparisons of family means. Parent-offspr ing correlations across environments seemed to depend on parental temp erature. For development time, heritabilities and evolvabilities were low at 14 OC compared to 28 degrees C. However, parent-offspring corre lations were relatively high when the progeny of parents tested at 14 degrees C were raised at the opposite extreme, suggesting that genetic variation can be enhanced when parents and offspring experience diffe rent conditions. CV(A)s and I(A)s for development time were lower than for fecundity, even when heritability estimates were similar in magni tude. Genetic variation for wing length was generally not affected by the temperature extremes, and genetic correlations across the extremes estimated from the parent-offspring comparison were close to 1. There was no evidence for tradeoffs between traits; rapid development time was associated with high fecundity at both the phenotypic and genetic levels. The findings highlight inherent difficulties of estimating gen etic parameters from parent-offspring comparisons when two generations experience different environmental extremes and also show how parent- offspring comparisons can lead to unexpected findings about the expres sion of genetic variation.