Wilder J A, Diaz T, O'Neill R J W, Kenney J, Hollocher H
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
Genet Res. 2002 Dec;80(3):177-85. doi: 10.1017/s0016672302005864.
We have isolated and characterized 77 novel microsatellites from two species, Drosophila dunni and Drosophila nigrodunni, which are closely related Caribbean-island endemics from the Drosophila cardini species group. These species are very distantly related to all other Drosophila from which microsatellites have previously been characterized. We find that the average length of microsatellites isolated in these species is quite small, with an overall mean length of 9.8 repeat units for dinucleotide microsatellites in the two study species. The nucleotide composition of dinucleotides differs between the two species: D. nigrodunni has a predominance of (AC/GT)n repeats, whereas D. dunni has equal numbers of (AC/GT)n and (AG/CT)n repeats. Tri- and tetranucleotide repeats are not abundant in either species. We assayed the variability of eight microsatellites in a closely related third species, Drosophila arawakana, using wild-caught individuals from the island of Guadeloupe. We found the microsatellites to be extremely variable in this population, with observed heterozygosities ranging from 0.541 to 0.889. DNA amplification trials suggest that these eight microsatellites are widely conserved across the D. cardini group, with five of the eight producing amplification products in every species tested. However, the loci are very poorly conserved over greater phylogenetic distances. DNA amplification of the microsatellite loci was unreliable in members of the closely related Drosophila quinaria, Drosophila calloptera, Drosophila guarani and Drosophila tripunctata species groups. Furthermore, these microsatellites could not be detected in the genome of Drosophila melanogaster, despite the conservation of microsatellite flanking regions at some loci. These data indicate that Drosophila microsatellite loci are quite short lived over evolutionary timescales relative to many other taxa.
我们从两个物种——邓氏果蝇（Drosophila dunni）和黑邓氏果蝇（Drosophila nigrodunni）中分离并鉴定了77个新的微卫星，它们是果蝇卡迪尼种组（Drosophila cardini species group）中关系密切的加勒比海岛特有物种。这些物种与之前已鉴定出微卫星的所有其他果蝇的亲缘关系都非常远。我们发现，在这些物种中分离出的微卫星平均长度相当短，在这两个研究物种中，二核苷酸微卫星的总体平均长度为9.8个重复单元。这两个物种中二核苷酸的核苷酸组成有所不同：黑邓氏果蝇以（AC/GT）n重复为主，而邓氏果蝇中（AC/GT）n和（AG/CT）n重复的数量相等。三核苷酸和四核苷酸重复在这两个物种中都不丰富。我们使用从瓜德罗普岛野生捕获的个体，检测了密切相关的第三个物种——阿拉瓦卡纳果蝇（Drosophila arawakana）中八个微卫星的变异性。我们发现这些微卫星在该种群中极具变异性，观察到的杂合度范围为0.541至0.889。DNA扩增试验表明，这八个微卫星在卡迪尼果蝇组中广泛保守，八个中有五个在每个测试物种中都产生了扩增产物。然而，在更大的系统发育距离上，这些位点的保守性非常差。在密切相关的奎纳瑞果蝇（Drosophila quinaria）、卡洛普特拉果蝇（Drosophila calloptera）、瓜拉尼果蝇（Drosophila guarani）和三斑果蝇（Drosophila tripunctata）种组的成员中，微卫星位点的DNA扩增不可靠。此外，尽管在某些位点微卫星侧翼区域保守，但在黑腹果蝇（Drosophila melanogaster）的基因组中无法检测到这些微卫星。这些数据表明，相对于许多其他分类群，果蝇微卫星位点在进化时间尺度上存在的时间相当短。
