Interspecific and intraspecific comparisons of the period locus in the Drosophila willistoni sibling species

The period (per) locus has received much attention in molecular evolutionstudies because it is one of the best studied "behavioral genes" andbecause it offers insight into the evolution of repetitive sequences. Westudied most of the coding region of per in Drosophila willistoni andconfirmed previously observed patterns of conservation and divergence amongdistantly related species. Five regions are so highly diverged that theycannot be aligned, whereas a region encompassing the PAS domain is veryconserved. Structural and nucleotide polymorphism patterns in thewillistoni group are not the same as those observed in previously studiedspecies. We sequenced the region homologous to the highly polymorphicthreonine-glycine repeat of D. melanogaster in multiple strains of D.willistoni, as well as in other members of willistoni group, and found anunusual amount of conservation in this region. However, the nextnonconserved region downstream in the sequence is quite variable andpolymorphic for the number of repeated glycines. The glycine codon usage issignificantly different in this glycine repeat as compared to other partsof the gene. We were able to plot the directionality of change in theglycine repeat region onto a phylogeny and find that the addition ofglycines is the general trend with the diversification of the willistonigroup.