GENETIC AND PHENOTYPIC VARIATION FOR FLIGHT ABILITY IN THE CACTOPHILIC DROSOPHILA SPECIES, D-ALDRICHI AND D-BUZZATII

The flight ability of Drosophila aldrichi (Patterson & Crow) and D. bu zzatii (Patterson and Wheeler) using tethered flights, was measured wi th respect to age-related changes, genetic variation and adult body si ze variation induced by rearing at different larval densities. Drosoph ila buzzatii flew for much longer than D. aldrichi, especially females , but age-related changes in flight duration were significant only for D. aldrichi. Effects of body size on flight ability were significant in D. buzzatii, but not in D. aldrichi. In D. buzzatii, there was a si gnificant genotype-environment interaction (larval density x line) for flight duration, with short and average flight duration isofemale lin es showing longer flights, but a long flight duration line shorter fli ghts as body size decreased (i.e., as larval density increased). Herit ability estimates for flight duration were similar in the two species, but flight duration showed no significant genetic correlations with d evelopmental time, body size or wing dimensions (except for one wing d imension in D. buzzatii). Although not significantly different between the species, heritabilities for life-history traits (adult size and d evelopmental time) showed contrasting patterns - with higher heritabil ity for body size (body weight and thorax length) in D. buzzatii, and higher for developmental time in D. aldrichi. In agreement with limite d previous field evidence, D. buzzatii is better adapted for colonizat ion than is D. aldrichi.