Molecular evolution of the period gene in Drosophila athabasca

We measured nucleotide variability within and between the three semispeciesof the Drosophila athabasca complex, at the period (per) gene by using apolymerase chain reaction-based four-cutter restriction- enzyme analysis.The levels of polymorphism varied considerably between the threesemispecies. Our results for per, combined with previous data for X-linkedallozymes, suggest that the X chromosome in the western- northernsemispecies is less variable than expected under an equilibrium-neutralmodel. Both the pattern of divergence between the semispecies and acladistic clustering of per haplotypes support the previously hypothesizedgrouping of eastern A and eastern B as the two most recently divergedsemispecies. A 21-bp in-frame segment in the region of per which sharessequence similarity with the neuronal development gene single minded isdeleted in all eastern A and eastern B flies examined but is present in allof the western-northern flies and all other published per sequences.Despite these hints that there may be significant differences at the pergene between the semispecies, especially the western-northern group versusthe two eastern groups, there is no compelling evidence that per isinvolved in the mating song differences between the semispecies.