Parental and developmental temperature effects on the thermal dependence of fitness in Drosophila melanogaster

Cross-generational effects refer to nongenetic influences of the parental p henotype or environment on offspring phenotypes. Such effects are commonly observed, but their adaptive significance is largely unresolved. We examine d cross-generational effects of parental temperature on offspring fitness ( estimated via a serial-transfer assay) at different temperatures in a labor atory population of Drosophila melanogaster. Parents were reared at 18 degr eesC, 25 degreesC, or 29 degreesC (T-par) and then their offspring were-rea red at 18 degreesC, 25 degreesC, or 29 degreesC (T-off) to evaluate several competing hypotheses (including an adaptive one) involving interaction eff ects of parental and offspring temperature on offspring fitness. The result s clearly show that hotter parents are better; in other words, the higher t he temperature of the parents, the higher the fitness of their offspring, i ndependent of offspring thermal environment. These data contradict the adap tive cross-generational hypothesis, which proposes that offspring fitness i s maximal when the offspring thermal regime matches the parental one. Flies with hot parents have high fitness seemingly because their own offspring d evelop relatively quickly, not because they have higher fecundity early in life.