Chromosome inversion polymorphisms inDrosophila melanogaster IV. Inversion and Adh allele frequency changes under selection for different development times

Polymorphism at the Adh and alpha Gpdh loci in Drosophila melanogaster: effects of rearing temperature on developmental rate, body weight, and some biochemical parameters

The role of developmental time in the world-wide cline of Adh and alpha Gpdh allele frequencies of Drosophila melanogaster, and the relationship with weight and some biochemical characters, were investigated. Experimental strains were constructed with different combinations of Adh and alpha Gpdh alleles but with similar genetic background. Developmental time, adult weight, protein-and triglyceride-content, and ADH and alpha GPDH enzyme activity were measured at a rearing temperature of 20, 25 and 29 degrees C. Genotype effects were found in all studied characters. In general the developmental times of genotypes were: AdhFF less than AdhFS less than AdhSS and alpha GpdhFF greater than alpha GpdhFS = alpha GpdhSS. Developmental time and adult weight were strongly affected by rearing temperature. Triglyceride content and ADH and alpha GPDH enzyme activity were slightly affected by temperature. Interactions between genotype and temperature effects were found for developmental rate, adult weight and protein content. No trade off was observed between developmental time on the one hand and adult weight, protein- and triglyceride-content, and ADH and alpha GPDH enzyme activity on the other hand. It is argued that developmental rate differences might be one of the underlying mechanisms of the world-wide cline of the Adh and alpha GPdh allele frequencies.

Allozyme polymorphism at the alpha Gpdh and Adh loci and fitness in Drosophila melanogaster

We have studied in Drosophila melanogaster the effects of allozyme variation at the alpha Gpdh and Adh loci on the following fitness components: female fecundity, egg hatchability, egg-to-adult survival under near-optimal and competitive conditions, rate of development under near-optimal and competitive conditions, and mating capacity of males. Significant effects of the alpha Gpdh locus on rate of development under competitive conditions (SS greater than FS greater than SS), and of the Adh locus on egg hatchability (FF = SS greater than FS) and egg-to-adult survival under competitive conditions (FF greater than SS = FS) were revealed. Possible natural selection mechanisms involved in the maintenance of allozyme polymorphisms at the alpha Gpdh and Adh loci are described. These mechanisms and the fitness of In(2L)t may account for the persistence and clinal distribution of the two allozyme polymorphisms in nature.

Observations on the extent and temporal stability of latitudinal clines for alcohol dehydrogenase allozymes and four chromosome inversions in Drosophila melanogaster

Previously we have presented evidence of large-scale latitudinal clines in the frequencies of four chromosome inversions and alleles at six enzyme loci in populations of D. melanogaster in Australasia, Asia and North America. Subsequent sampling by others in Japan and western U.S.A. has failed to repeat this observation for the steepest of the clines (alcohol dehydrogenase and the four chromosome inversions). We argue that this failure reflects the few populations and small latitudinal range sampled in these later studies. From extensive sampling over a long latitudinal transect in Australasia we here document Adh and inversion clines which are virtually identical to those originally obtained in different Australian populations four years earlier. We also repeat our observation that the Adh cline is largely independent of the cline in the linked inversion In(2L)t. We therefore retain our original conclusion that these polymorphisms are subject to natural selection. However the new Australasian data do not indicate an association between Adh and maximum rainfall which had been evident in the earlier data for Australasia, Asia and North America. We therefore retract our claim that the selective agent on Adh is related to rainfall.