Phylogeny and evolution of the Drosophila nasuta subgroup based on mitochondrial ND4 and ND4L gene sequences

The sequences of the mitochondrial ND4 gene (1339 bp) and the ND4L gene (29 0 bp) were determined for all the 14 extant taxa of the Drosophila nasuta s ubgroup The average A + T content of ND4 genes is 76.5% and that of ND4L ge nes is 83.5%. A total of 114 variable sites were scored. The ND4 gene seque nce divergence ranged from 0 to 5.4% within the subgroup. The substitution rate of the ND4 gene is about 1.25% per million years. The base substitutio n of the genesis strongly transition biased. Neighbor-joining and parsimony were used to construct a phylogeny based on the resultant sequence data se t. According to these trees, five, distinct mtDNA clades can be identified. D. niveifrons represents the most diverged lineage. D, sulfurigaster bilim bata and D. kepulauana form two independent lineages. The other two clades are the kohkoa complex and the albomicans complex. The Kohkoa complex consi sts of D. sulfurigaster sulfurigaster, D. pulaua, D. kohkoa, and Taxon-F. T he albomicans complex can be divided into two groups: D. nasuta, D. sulfuri gaster neonasuta, D. sulfurigaster albostrigata, and D.. albomicans from Ch iangmai form one group; and D. pallidifrons, Taxon-I, Taxon-J, and D. albom icans from China form the other group. High genetic differentiation was fou nd among D. albomicans populations. Based on our phylogenetic results, we h ypothesize that D. niveifrons diverged first from the D, nasuta subgroup in Papua New Guinea about 3.5 Mya. The ancestral population spread to the nor th and when it reached Borneo, it diversified sequentially into the kohkoa complex, D. s. bilimbata, and D. kepulauana. About 1 Mya, another radiation occurred when the ancestral populations reached the Indo-China Peninsula, forming the albomicans complex. Discrepancy between morphological groupings and phylogenetic results suggests that the male morphological traits may n ot be orthologous. (C) 1999 Academic Press.