The aim of the present work was to identify the genes that played a role in ecological adaptation in D. melanogaster. This species, which originated in Africa, successfully adapted to a broad range of climates during the last 100.000 years. To find the genes involved, I used two different approaches: (1) a genomic region containing several ecologically relevant candidate genes and putatively carrying footprints of selection was investigated using selective sweep mapping, and (2) cold tolerance that might have been an important phenotype for the adaptation to the temperate climates was investigated using a QTL analysis.
Using the technique of selective sweep mapping pioneered in the Stephan’s group, I detected evidence that recent strong positive selection has been acting on a small DNA region of 2.7 kb overlapping with the 3’ end of the HDAC6 gene in the ancestral African population. This gene codes for a newly characterized cell stress surveillance factor. HDAC6 is an unusual histone-deacetylase. It is localized in the cytoplasm and has a ubiquitin-binding and a tubulin-deacetylase activity. These properties make HDAC6 a key regulator of cytotoxic stress resistance.
The phenotypic analyses show that the African and the European populations have very strong cold tolerance differences. By removing the effects of the autosomes, I showed that a significant amount of the phenotypic variance is due to genetic factors carried by the X chromosome. These factors were then more precisely mapped to two genomic regions of the X chromosome. By comparing the present results with other association studies and the Gene Ontology database, it was possible to determine a list of candidate genes influencing cold tolerance in D. melanogaster. As this list is limited to a very small number of genes, additional investigations for footprints of selection in these regions may be used to confirm their role in ecological adaptation
