Frequency and temperature dependent selection at the alcohol dehydrogenase-1 locus of Drosophila buzzatii

Genotype frequencies at the alcohol dehydrogenase-1 (Adh-1) locus of D. buzzatii were analysed for deviations from Hardy-Weinberg equilibria in the progeny of laboratory populations established at five initial Adh-1b allele frequencies and kept at either 18 degrees C, 25 degrees C or 30 degrees C. At 25 degrees C, no observed genotype frequencies were significantly different from Hardy-Weinberg expectations. Observed frequencies of heterozygotes were generally less than expected for populations at 18 degrees C and 30 degrees C. Fitness differences among genotypes were greater in males than in females, with Adh-1b homozygotes having highest fitness at 18 degrees C and Adh-1c homozygotes having highest fitness at 30 degrees C. The results are discussed in relation to previous field and laboratory studies on D. buzzatii and to the Adh polymorphism of D. melanogaster.