EVOLUTION AND PHYLOGENETIC UTILITY OF THE PERIOD GENE IN LEPIDOPTERA

Evolution and phylogenetic utility of the period gene are explored thr ough sequence analysis of a relatively conserved 909-bp fragment in 26 lepidopteran species. Taxa range from tribes to superfamilies, primar ily within the putative clade Macrolepidoptera plus near outgroups, an d include both strongly established and problematic groupings. Their d ivergence dates probably range from the late Cretaceous through much o f the Tertiary. Comparisons within the same set of closely related spe cies show that amino acid substitutions in period occur 4.9 and 44 tim es as frequently as they do in two other nuclear genes-dopa decarboxyl ase and elongation factor-1 alpha, respectively. In contrast, rates of observed synonymous substitution are within 60% of each other for the se three genes. Synonymous changes in period approach saturation by th e family level, whereas nonsynonymous and amino acid divergences acros s the Macrolepidoptera are less than half the maximal values reported for this gene. Phylogenetic analyses of period strongly supported grou pings at the family level and below. In contrast to previous analyses at this level with other nuclear genes, much of the information lies i n nonsynonymous change. Relationships up to the superfamily level were recovered with decreasing effectiveness, and little, if any, signal w as apparent regarding relationships among superfamilies. This could re flect rapid radiation of the superfamilies, however, rather than satur ation in the period locus; thus, period, in combination with other gen es, remains a plausible candidate for approaching the difficult proble ms of lepidopteran family and superfamily relationships.