Responses to Developmental Temperature Fluctuation in Life History Traits of Five Drosophila Species (Diptera: Drosophilidae) from Different Thermal Niches

Simple Summary Most laboratory experiments on insects to date have been conducted using constant temperature settings. Even when the purpose of the study was to investigate effects of temperature, insects have mostly been kept at different but constant temperatures ignoring natural variation in temperature. Here we investigated effects of simple daily temperature fluctuation (22.5/27.5 degrees C and 20/30 degrees C) on some development characteristics in five species of fruit flies (Drosophila) originating from areas with different temperature profiles. We demonstrated how species of the same genus can show substantial differences when developing at fluctuating temperatures not always predictable by development at comparable constant temperature (25 degrees C). Temperature has profound effects on biochemical processes as suggested by the extensive variation in performance of organisms across temperatures. Nonetheless, the use of fluctuating temperature (FT) regimes in laboratory experiments compared to constant temperature (CT) regimes is still mainly applied in studies of model organisms. We investigated how two amplitudes of developmental temperature fluctuation (22.5/27.5 degrees C and 20/30 degrees C, 12/12 h) affected several fitness-related traits in five Drosophila species with markedly different thermal resistance. Egg-to-adult viability did not change much with temperature except in the cold-adapted D. immigrans. Developmental time increased with FT among all species compared to the same mean CT. The impact of FT on wing size was quite diverse among species. Whereas wing size decreased quasi-linearly with CT in all species, there were large qualitative differences with FT. Changes in wing aspect ratio due to FT were large compared to the other traits and presumably a consequence of thermal stress. These results demonstrate that species of the same genus but with different thermal resistance can show substantial differences in responses to fluctuating developmental temperatures not predictable by constant developmental temperatures. Testing multiple traits facilitated the interpretation of responses to FT in a broader context.