Llopart Ana, Elwyn Susannah, Lachaise Daniel, Coyne Jerry A
Department of Ecology and Evolution, The University of Chicago, 1101 East 57 Street, Chicago, Illinois 60637, USA.
Evolution. 2002 Nov;56(11):2262-77. doi: 10.1111/j.0014-3820.2002.tb00150.x.
Drosophila yakuba is a species widespread in Africa, whereas D. santomea, its newly discovered sister species, is endemic to the volcanic island of São Tomé in the Gulf of Guinea. Drosophila santomea probably formed after colonization of the island by its common ancestor with D. yakuba. The two species differ strikingly in pigmentation: D. santomea, unlike the other eight species in the D. melanogaster subgroup, almost completely lacks dark abdominal pigmentation. D. yakuba shows the sexually dimorphic pigmentation typical of the group: both sexes have melanic patterns on the abdomen, but males are much darker than females. A genetic analysis of this species difference using morphological markers shows that the X chromosome accounts for nearly 90% of the species difference in the area of abdomen that is pigmented and that at least three genes (one on each major chromosome) are involved in each sex. The order of chromosome effects on pigmentation area are the same in males and females, suggesting that loss of pigmentation in D. santomea may have involved the same genes in both sexes. Further genetic analysis of the interspecific difference between males in pigmentation area and intensity using molecular markers shows that at least five genes are responsible, with no single locus having an overwhelming effect on the trait. The species difference is thus oligogenic or polygenic. Different chromosomal regions from each of the two species influenced pigmentation in the same direction, suggesting that the species difference (at least in males) is due to natural or sexual selection and not genetic drift. Measurements of sexual isolation between the species in both light and dark conditions show no difference, suggesting that the pigmentation difference is not an important cue for interspecific mate discrimination. Using DNA sequence differences in nine noncoding regions, we estimate that D. santomea and D. yakuba diverged about 400,000 years ago, a time similar to the divergences between two other well-studied pair of species in the subgroup, both of which also involved island colonization.
雅库布果蝇是一种广泛分布于非洲的物种，而其新发现的姐妹种圣多美果蝇则仅分布于几内亚湾的圣多美火山岛。圣多美果蝇可能是在其与雅库布果蝇的共同祖先殖民该岛后形成的。这两个物种在色素沉着方面存在显著差异：与黑腹果蝇亚组中的其他八个物种不同，圣多美果蝇几乎完全没有深色的腹部色素沉着。雅库布果蝇表现出该类群典型的性二态色素沉着：两性腹部都有黑色斑纹，但雄性比雌性颜色深得多。利用形态学标记对这种物种差异进行的遗传分析表明，X染色体在有色素沉着的腹部区域的物种差异中占近90%，并且每种性别至少有三个基因（每个主要染色体上一个）参与其中。染色体对色素沉着区域的影响顺序在雄性和雌性中是相同的，这表明圣多美果蝇色素沉着的丧失可能在两性中涉及相同的基因。使用分子标记对雄性色素沉着区域和强度的种间差异进行的进一步遗传分析表明，至少有五个基因起作用，没有一个单一基因座对该性状有压倒性影响。因此，物种差异是寡基因或多基因的。来自两个物种的不同染色体区域对色素沉着的影响方向相同，这表明物种差异（至少在雄性中）是由于自然选择或性选择，而不是遗传漂变。在明亮和黑暗条件下对这两个物种之间的性隔离进行测量，结果没有差异，这表明色素沉着差异不是种间配偶识别的重要线索。利用九个非编码区域的DNA序列差异，我们估计圣多美果蝇和雅库布果蝇在大约40万年前分化，这与该亚组中另外两对经过充分研究的物种之间的分化时间相似，这两对物种的分化也都涉及岛屿殖民。
