Searching for genes involved in the adaptation of Drosophila melanogaster to the European climate

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.