Rejection of the beneficial acclimation hypothesis (BAH) for short term heat acclimation inDrosophila nepalensis

Beneficial acclimation hypothesis (BAH) is the phenotypic plasticity in response to changing environments which enables organisms to enhance their fitness. In recent years, however, BAH has received vigorous criticism and is still debatable. In this study, we tested thermal hardiness phenotypes (melanization, chill coma recovery, heat knockdown and percentage survival) on adult and pre-adult stages ofDrosophila nepalensis, reared in different thermal environments (14, 17, 21 and 25 degrees C) to check whether increasing natural surrounding temperature and acclimation limit towards environmental change is detrimental or beneficial. Results showed that rearingD. nepalensisat higher temperatures (21 and 25 degrees C) reduces its melanization and cold hardiness but improves heat knockdown times. When temperature was raised to 26.2 degrees C (0.6 degrees C above the upper thermal maxima), to determine the short-term acclimation effects, survival and fitness of adults diminished approximately 1.5 to 2 folds. These results suggest thatD. nepalensishas long-term developmental acclimation to both heat and cold which would be extremely beneficial as temperatures and climates alter in the region due to global warming. However, a lack of short-term heat acclimation suggests that rapid shifts in thermal extreme could be detrimental toD. nepalensis.