Background: Physiological tolerances are important determinants of the biogeography of species. Questions: What is the relationship between thermal tolerance and the biogeographic origin of species? What are the relationships between thermal tolerance and life-history traits? Organisms: Four Drosophila species, two from a tropical biogeographic area (D. melanogaster and D. simulans) and two from a temperate geographic zone in the Andes mountains (D. pavani and D. gaucha). Methods: We assessed upper and lower lethal temperature. We used thermal limits to construct a thermal tolerance polygon that represents the total thermal range of each species after acclimation at different ambient temperatures. We also measured differences in life history (fertility and egg-to-adult viability) between species. Conclusions: Both temperate species have broader thermal tolerance ranges than either tropical species. But temperate species have lower fitness at higher temperatures than tropical species,
