Interplay between habitat fragmentation and climate change:Inbreeding affects the response to thermal stress in <i>Drosophila melanogaster</i>

Climate change, exerting thermal stress, and habitat destruction and fragmentation, resulting in genetic drift and inbreeding, are amongst the most disturbing human activities that endanger global biodiversity. We studied the interplay between these 2 processes using Drosophila melanogaster as a model organism and investigated how inbreeding affects the response to thermal stress. We found that both inbreeding and thermal stress negatively affect morphological traits (orbital bristle number, wing width and wing length) as well as a fitness trait (egg-to-adult viability). Most importantly, we observed a significant interaction between inbreeding and thermal stress. Inbred populations suffered considerably more from thermal stress than non-inbred populations for these traits. Moreover, the variation among inbred populations was large: some populations were affected only slightly by thermal stress, but others became extremely sensitive to thermal stress, particularly in egg-to-adult survival. This shows that inbreeding does significantly influence the response to thermal stress, thereby greatly enhancing the effects of temperature stress. We also tested if the effects of inbreeding and thermal stress were reflected in changes in the level of fluctuating asymmetry, in order to determine if this measure can be used as a reliable biomonitor. Although we observed some changes in fluctuating asymmetry under stress, the results are far from unequivocal. We concluded that inbreeding and thermal stress act synergistically and argue that the consequences of climate change and habitat fragmentation should preferably be studied in combination rather than in isolation.