Environment-dependent fitness differences in Drosophila melanogaster: temperature, domestication and the alcohol dehydrogenase locus

Abstract

a) Phenotypic fitnesses were estimated over the temperature range 15° C to 29° C for genotypes at the alcohol dehydrogenase (Adh) locus. The traits measured were egg and larval survival, development time and mating ability in single generation experiments, and total fitness by gene frequency changes in discrete generation populations. b) Significant temperature-dependent fitness associations involving the Adh locus were obtained for isofemale strains which had been in the laboratory for eighteen months. Heterozygote advantage was general in the single generation experiments, and in the populations the AdhF allele increased in frequency. c) In contrast, populations obtained directly from the field did not show these fitness associations. It was not therefore possible to attribute the genotypic fitness differences detected for the laboratory strains directly to the Adhlocus. Indeed, the contrast between the laboratory-adapted and field collected flies may provide a model of likely change under domestication whereby the higher variability of the laboratory strains may be a manifestation of the “stress” involved in the adaptation of populations to laboratory conditions. d) The results emphasise the need to commence at the phenotypic level in attempting to understand fitness relationships in natural populations and it is suggested that direct assessments of the effects of environmental stresses of ecological significance may provide an initial strategy.