INTERSPECIFIC AND INTRASPECIFIC COMPARISONS OF THE PERIOD LOCUS IN THE DROSOPHILA-WILLISTONI SIBLING SPECIES

The period (per) locus has received much attention in molecular evolut ion studies because it is one of the best studied ''behavioral genes'' and because it offers insight into the evolution of repetitive sequen ces. We studied most of the coding region of per in Drosophila willist oni and confirmed previously observed patterns of conservation and div ergence among distantly related species. Five regions are so highly di verged that they cannot be aligned, whereas a region encompassing the PAS domain is very conserved. Structural and nucleotide polymorphism p atterns in the willistoni group are not the same as those observed in previously studied species. We sequenced the region homologous to the highly polymorphic threonine-glycine repeat of D. melanogaster in mult iple strains of D. willistoni, as well as in other members of the will istoni group, and found an unusual amount of conservation in this regi on. However, the next nonconserved region downstream in the sequence i s quite variable and polymorphic for the number of repeated glycines. The glycine codon usage is significantly different in this glycine rep eat as compared to other parts of the gene. We were able to plot the d irectionality of change in the glycine repeat region onto a phylogeny and find that the addition of glycines is the general trend with the d iversification of the willistoni group.