Resistance to thermal stress in desert Drosophila

1. Four species of Drosophila are endemic to the Sonoran Desert of North America where daily and seasonal high temperatures exceed those experienced by other species in this genus. The close association between these species and their cactus hosts means that they reside only in the desert and raises the question as to whether they are better able to survive heat stress than are non-desert species of Drosophila. The tolerance of adult flies of the four desert species D. mojavensis, D. nigrospiracula, D. pachea and D. mettleri and the cosmopolitan D. simulans to acute heat stress was tested. 2. There was considerable variability among the desert endemic species with respect to survival following heat exposure. Two species, D. mojavensis and D, pachea, were more resistant at 44 degrees C and 46 degrees C than the others, with D. mettleri exhibiting similar heat stress resistance to D. simulans. 3. While there was no consistent influence of gender on heat resistance, younger flies (l-day-old) showed significantly greater survival than did older flies (7- or 14-days old).