Phenotypic plasticity for life-history traits inDrosophila melanogaster. III. Effect of the environment on genetic parameters

Abstract

SummaryWe estimated genetic and environmental variance components for developmental time and dry weight at eclosion in Drosophila melanogaster raised in ten different environments (all combinations of 22, 25 and 28 °C and 05, 1 and 4% yeast concentration, and 0-25% yeast at 25 °C). We used six homozygous lines derived from a natural population for complete diallel crosses in each environment. Additive genetic variances were consistently low for both traits (h 2 around 10%). The additive genetic variance of developmental time was larger at lower yeast concentrations, but the heritability did not increase because other components were also larger. The additive genetic effects of the six parental lines changed ranks across environments, suggesting a mechanism for the maintenance of genetic variation in heterogenous environments.The variance due to non-directional dominance was small in most environments. However, there was directional dominance in the form of inbreeding depression for both traits. It was pronounced at high yeast levels and temperatures but disappeared when yeast or temperature were decreased. This meant that the heterozygous flies were more sensitive to environmental differences than homozygous flies. Because dominance effects are not heritable, this suggests that the evolution of plasticity can be constrained when dominance effects are important as a mechanism for plasticity.

Stress temperatures and quantitative variation in Drosophila melanogaster

“…We also recorded the same effect for another morphological character, sternopleural chaeta number, although in this case it was less marked. By contrast, searches for the effect of stress on fitness characters often seem to give equivocal results (Murphy et al, 1983;Gebhardt & Stearns, 1992 -temperature effects; the present work). This is somewhat surprising as hypotheses predicting an increase of variation at stress (Parsons, 1982;Hoffmann & Parsons, 1991;Zhivotovsky et al, 1996Zhivotovsky et al, , 1997 put special emphasis on fitness components.…”

“…Using a diallel experimental design, Gebhardt & Stearns (1992) (Gebhardt & Stearns, 1988). The lack of temperature effect on genetic variation might be explained by the fact that these authors did not use temperatures that could cause extreme stress.…”

“…Rearing under stressful conditions has been shown to increase phenotypic variation in developmental time (Parsons, 1961;Gebhardt & Stearns, 1988, 1992, dry weight at eclosion (Gebhardt & Stearns, 1988), thorax length (Robertson, 1960;Imasheva et al, 1997), wing length (Tantawy & Mallah, 1961;David et al, 1994;Lazebny et al, 1996), ovariole number (Delpuech et al, 1995), and sternopleural chaeta number (Parsons, 1961;Imasheva et al, 1997). Types of stress used were extreme temperatures (Parsons, 1961;Tantawy & Mallah, 1961;David et al, 1994;Imasheva et al, 1997), deficient larval diet (Robertson, 1960;Gebhardt & Stearns, 1988, 1992, and larval crowding (Parsons, 1961;Lazebny et al, 1996).…”

“…However, the effect of stress on genetic variation is under dispute (Barton & Turelli, 1989) as the available evidence is less clear-cut and the results are often inconsistent (see, e.g. Murphy et al, 1983;Gebhardt & Stearns, 1988, 1992.…”

Factors contributing to the maintenance of the genetic polymorphism at the locus LDH-B in the pool frog,Rana lessonae

“…Temperature and the amount of food have repeatedly been shown to be environmental gradients along which reaction norms of genotypes may cross (e.g., Powers et al 1993 for LDH-B) and life histories and their quantitative genetics may vary according to temperature and food level (e.g., Berven et al 1979;Gebhardt and Stearns 1992;Ebert et al 1993;Semlitsch 1993b;Newman 1994). Because LDH-B is involved in the metabolism of carbohydrates, and food composition may affect tadpole life histories (Steinwascher and Travis 1983;Kupferberg et al 1994), we also manipulated the carbohydrate content of the food.…”