Fitness of wild-caught Drosophila melanogaster females: allozyme variants of GPDH, ADH, PGM, and EST

We have collected several hundred Drosophila melanogaster flies (near Davis , California), isolated them individually, without anesthesia, at the colle cting site, and estimated the fitness components of the wild-caught females under different environmental conditions. The fitness parameters measured are fecundity, oviposition rate, and productivity (egg-to-adult viability, development rate, and number of progeny). The environmental variables are t wo temperatures (22 degrees C and 28 degrees C) and two densities ('scant' and 'crowded'). After the fitness measurements are completed for each indiv idual female, its genotype is determined at four loci encoding enzymes: GPD H and ADH, located on chromosome II and PGM and EST-C, located on chromosom e III. Density has a large significant effect on productivity; temperature has significant effects on fecundity, oviposition rate, and development rat e. The experiments show that allozyme polymorphisms are associated with sel ection effects. Fitness differences between allozyme genotypes occur for al l fitness components, except oviposition rate. But which genotype is superi or depends on the environmental conditions; heterozygotes exhibit higher fi tness than homozygotes in a number of cases, but inferior in others. A uniq ue feature of the present experiments is that the experimental flies are wi ld-caught females rather than laboratory-bred individuals.