No inbreeding depression for low temperature developmental acclimation across multiple Drosophila species

Populations are from time to time exposed to stressful temperatures. Their thermal resistance levels are determined by inherent and plastic mechanisms, which are both likely to be under selection in natural populations. Previous studies on Drosophila species have shown that inherent resistance is highly species specific, and differs among ecotypes (e.g., tropical and widespread species). Apart from being exposed to thermal stress many small and fragmented populations face genetic challenges due to, for example, inbreeding. Inbreeding has been shown to reduce inherent resistance levels toward stressful temperatures, but whether adaptation to thermal stress through plastic responses also is affected by inbreeding is so far not clear. In this study, we test inherent cold resistance and the ability to respond plastically to temperature changes through developmental cold acclimation in inbred and outbred lines of five tropical and five widespread Drosophila species. Our results confirm that tropical species have lower cold resistance compared to widespread species, and show that (1) inbreeding reduces inherent cold resistance in both tropical and widespread species, (2) inbreeding does not affect the ability to respond adaptively to temperature acclimation, and (3) tropical species with low basal resistance show stronger adaptive plastic responses to developmental acclimation compared to widespread species.