Field tests reveal genetic variation for performance atlow temperatures in Drosophila melanogaster

1. Physiological and evolutionary responses underlying thermal adaptation and acclimation

are often investigated under controlled laboratory conditions. Such studies may fail to assess

ecologically relevant parameters as they do not account for the complexity of the natural

environment.

2. We investigated a population of Drosophila melanogaster for performance at low temperature

conditions in the field using release recapture assays and in the laboratory using standard cold

resistance assays. The aim of the study was to get a better understanding of the nature and

underlying mechanisms of the trait measured in field recapture studies and the association

between field performance and fitness measures estimated in the laboratory.

3. We performed one generation of selection on the ability to reach a resource at low temperature

under field conditions. Flies that reached a resource (‘mobile') and those that never left the

release site (‘stationary') were reared to the F1 and F2 generation in the laboratory. Subsequent

field releases with these flies demonstrated a clear genetic differentiation between mobile and stationary

flies in their ability to reach resources at low temperatures in the field. This indicates that

mobility at low temperature is under additive genetic influence. In contrast mobile and stationary

flies were generally indistinguishable when tested in standard laboratory tests of cold performance.

The genetic differentiation between the two sub-populations was not linked to allelic

variation in known candidate genes for cold adaptation. However, using transcriptomics we

identified new candidate genes (transcripts) and pathways that differed between the mobile and

stationary flies.

4. The current study reveals an irregular relationship between cold performance in the field and

in the laboratory. Based on these results, we suggest that the ecological relevance of laboratory

assays should be evaluated more critically in studies of thermal adaptation and hardening ⁄

acclimation.