Cold tolerance in Sonoran Desert Drosophilaspecies

Abstract

I examined resistance to cold temperature in seven Drosophila species from different habitats to determine the lower limits of cold tolerance. Three separate tests were administered to measure the: (1) response to a cold-shock exposure; (2) extent to which a short-term survival strategy, rapid cold hardening, was utilized by each species; and (3) degree to which each species would respond to a prolonged exposure at 0°C. As expected, the temperate-montane species, D. pseudoobscura, was the most cold-tolerant, whereas the least cold-tolerant was the tropical species, D. paulistorum. The two cosmopolitan species, D. hydei and D. melanogaster, and the three Sonoran Desert endemic species, D. mojavensis, D. nigrospiracula, and D. mettleri, demonstrated intermediate levels of cold-tolerance. Of the five species tested for rapid cold hardening, all exhibited the response, including the tropical representative. The results for the 0°C test paralleled the results of the cold shock test. The desert species tested proved surprisingly cold-tolerant, especially D. mojavensis.