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 (290 bp) were determined for all the 14 extant taxa of the Drosophila nasuta subgroup The average A + T content of ND4 genes is 76.5% and that of ND4L genes is 83.5%. A total of 114 variable sites were scored. The ND4 gene sequence 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 substitution of the genesis strongly transition biased. Neighbor-joining and parsimony were used to construct a phylogeny based on the resultant sequence data set. According to these trees, five, distinct mtDNA clades can be identified. D. niveifrons represents the most diverged lineage. D, sulfurigaster bilimbata and D. kepulauana form two independent lineages. The other two clades are the kohkoa complex and the albomicans complex. The Kohkoa complex consists of D. sulfurigaster sulfurigaster, D. pulaua, D. kohkoa, and Taxon-F. The albomicans complex can be divided into two groups: D. nasuta, D. sulfurigaster neonasuta, D. sulfurigaster albostrigata, and D.. albomicans from Chiangmai form one group; and D. pallidifrons, Taxon-I, Taxon-J, and D. albomicans from China form the other group. High genetic differentiation was found among D. albomicans populations. Based on our phylogenetic results, we hypothesize that D. niveifrons diverged first from the D, nasuta subgroup in Papua New Guinea about 3.5 Mya. The ancestral population spread to the north 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 not be orthologous. (C) 1999 Academic Press.

太平洋西部边界及边界流对赤道暖水库形成和演化的影响

A model of equatorial ocean is used to study the roles of the Pacific western boundary and the Mindanao Current (MC) in the evolution of the equatorial warm pool. The model consists of the single baroclinic mode of a two-layer ocean, with the parameterization of the anomalous increment of the interface representing the SST difference from its long-term-space-mean. The ocean is driven by a wind path in the middle ocean with a real or an artificial geometry assigned at the western and eastern boundaries. In order to test the role of the MC, the western boundary current is introduced into the model by a boundary condition at a position, real and unreal, respectively. The model experiments show that the warm pool, which is insensitive to the longitudinal width of the wind band in middle ocean, results mainly from the accumulation o the eastly-drifted warm water in the equatorial western Pacific. It is the dominant factor for the formation of the warm pool that, at a very low latitude, the Papua New Guinea coast intersects the longitudinally lined Philippine Islands at an obtuse angle. In contrast, the western Atlantic boundary, which inclines poleward from the equator at some 135 degrees, could guide the warm water there moving to a higher latitude. On the other hand, the equatorial warm pool in the western equatorial Pacific is very sensitive to the assignment of th Mindanao Current at 7.5°N and displaces southward, with a stronger southern branch than the northern one. We attribute this asymmetry to the combined effect of the western boundary and the MC upon the equatorial warm away from the equator. A by-product of our solutions is the possible mechanism of the "secondary warm pool" in the eastern Pacific north of the equator. It is suggested that, mainly or partly, the "secondary warm pool" results from the cooperation of the southeast monsoon in eastern Pacific and the eastern boundary hindering the propagation of the Kelvin wave poleward alongshore.