ACCLIMATION AND ADAPTIVE-BEHAVIOR OF DROSOPHILA-ROBUSTA AND D-TRIPUNCTATA ADULTS IN RESPONSE TO COMBINED TEMPERATURE AND DESICCATION STRESS

The behavioral responses of adult female and male Drosophila robusta a nd D. tripunctata to combined temperature and desiccation stress were compared on a temperature gradient [temperature range 14.7 to 27.7 C; vapor pressure deficit range 8 (cool end) to 19 g/m(3) (warm end)]. Dr osophila tripunctata preferred significantly lower temperatures than D . robusta Because previous work showed D. tripunctata to have signific antly lower adult viability than D. robusta at high temperature, this behavioral response is adaptive. Both species showed an acclimation re sponse and preferred higher temperatures after a two day prior exposur e to a high and stressful temperature (26 C). Adults from stocks which had been cultured a longer time in the laboratory preferred significa ntly different (higher) temperatures. Adults from older stocks also sh owed a significantly smaller acclimation response than flies from youn ger stocks. Both of these results are consistent with genetic changes having occurred in the stocks during the years of laboratory culturing .