Natural variation within a clock gene of Drosophila melanogaster : a phenotypic and molecular analysis

The clock gene period encodes a repetitive series of Threonine-Glycine (Thr-Gly) pairs in D. melanogaster. This sequence is polymorphic in length and shows a clinal distribution in Europe, whereby the shorter length variants are more frequent in warmer regions and the longer ones in colder areas. A series of new correlations performed with the European population data suggests that thermal selection may be a factor in generating the cline. DNA sequence analysis of various Thr-Gly haplotypes supports a model where the (Thr-Gly)2o and (Thr-Gly)23 alleles are considered as ancestral, since all variants can be derived from them. A reciprocal cline is observed for the (Thr-Glyho length valiant in eastern Australia, suggesting that selection may be maintaining the polymorphism, and a further correlation of temperature with allele frequency suggests, as in European populations, that the cline may be thermally mediated. However, the other major allele the (Thr-Gly)17 was spatially homogenous. The temperature compensation of the clock was examined by investigating the freerunning locomotor activity cycles of different natural ThrGly length variants from Europe and Australia. A relationship between Thr-Gly length and temperature compensation which could help explain the continental spatial differences was observed. Locomotor activity profiles in light/dark cycles were also examined in the European variants, and revealed subtle phenotypic differences between the Thr-Gly length variants that could also contribute to the observed clinal patterns. The energy expenditure of different Thr-Gly length variants was also measured and revealed behavioural adaptations for possible fitness advantages. Throughout the behavioural analyses there was also evidence that the structural (Thr-Gly)3 motif played an important role in the temperature compensation mechanism and energy expenditure of the fly.