Tsaur S C, Ting C T, Wu C I
Department of Ecology and Evolution, University of Chicago, Illinois 60637, USA.
Mol Biol Evol. 1998 Aug;15(8):1040-6. doi: 10.1093/oxfordjournals.molbev.a026002.
The evolution of the gene for a male ejaculatory protein, Acp26Aa, has been shown to be driven by positive selection when nonsibling species in the Drosophila melanogaster subgroup are compared. To know if selection has been operating in the recent past and to understand the details of its dynamics, we obtained DNA sequences of Acp26Aa and the nearby Acp26Ab gene from 39 D. melanogaster chromosomes. Together with the 10 published sequences, we analyzed 49 sequences from five populations in four continents. The southern African population is somewhat differentiated from all other populations, but its nucleotide diversity is lower at these two loci. We find the following results for Acp26Aa: (1) The R: S (replacement : silent changes) ratio is significantly higher in the between-species comparisons than in the within-species data by the McDonald and Kreitman test. Positive selection is probably responsible for the excess of amino acid replacements between species. (2) However, within-species nucleotide diversity is high. Neither the Tajima test nor the Fu and Li test indicates a reduction in nucleotide diversity due to positive selection in the recent past. (3) The newly derived nucleotides in D. melanogaster are at high frequency significantly more often than predicted by the neutral equilibrium. Since the nearby Acp26Ab gene does not show these patterns, these observations cannot be attributed to the characteristics of this chromosomal region. We suggest that positive selection is active, but may be weak, for each amino acid change in the Acp26Aa gene.
当比较黑腹果蝇亚组中的非同胞物种时，已表明雄性射精蛋白基因Acp26Aa的进化是由正选择驱动的。为了了解近期是否存在选择作用并了解其动态细节，我们从39条黑腹果蝇染色体中获得了Acp26Aa及附近Acp26Ab基因的DNA序列。连同已发表的10条序列，我们分析了来自四大洲五个种群的49条序列。非洲南部种群与所有其他种群有所分化，但其在这两个基因座处的核苷酸多样性较低。对于Acp26Aa，我们发现以下结果：（1）通过麦克唐纳和克雷特曼检验，种间比较中的R：S（替换：沉默变化）比率显著高于种内数据。种间氨基酸替换过多可能是正选择所致。（2）然而，种内核苷酸多样性很高。 Tajima检验和Fu与Li检验均未表明由于近期正选择导致核苷酸多样性降低。（3）黑腹果蝇中新衍生的核苷酸以高频率出现的情况明显比中性平衡预测的更为频繁。由于附近的Acp26Ab基因未显示这些模式，因此这些观察结果不能归因于该染色体区域的特征。我们认为，对于Acp26Aa基因中的每个氨基酸变化，正选择是活跃的，但可能很弱。
