Variation in body size and life history traits in Drosophila aldrichi and D-buzzatii from a latitudinal cline in eastern Australia

Latitudinal variation in thorax and wing size traits was studied in wild-ca ught flies of the cactophilic Drosophila species, D. aldrichi and D. buzzat ii, and their laboratory-reared progeny. The flies originated from five pop ulations in Queensland, Australia, spanning an 800-km transect. The laborat ory flies were reared at controlled densities and three temperatures, 20, 2 5, and 30 degreesC. We measured the same traits for the laboratory-reared f lies as for the wild-caught flies, plus developmental time and viability. L atitudinal variation in wild-caught flies of both species followed a simila r pattern for all linear size traits, with size generally increasing from n orth to south, but with flies from one intermediate locality markedly small er. A drier environment at this locality and weather conditions immediately prior to collection, most likely explain the reduced size. Laboratory-rear ed D. aldrichi from this locality also were smaller than those from other l ocalities, and had the fastest developmental time and highest viability. In laboratory-reared flies, body size traits did not show any clear trend to increase with latitude. The patterns of change with latitude were different between species, with D. aldrichi more similar in pattern to that of the n atural populations. D, aldrichi had comparatively higher coefficients of va riation in the laboratory-reared flies and lower viability at all temperatu res. However, fluctuating asymmetry was lower in D. aldrichi in both wild-c aught and laboratory-reared flies. The differences among populations of D. aldrichi for all traits were much larger than for D. buzzatii. As these dif ferences in the laboratory-reared flies are expected to be largely genetic, they most likely reflect adaptation to specific (unknown) environmental fa ctors that do not show linear latitudinal variation on the geographical sca le studied.