Spicer Greg S, Jaenike John
Institute of Molecular Medical Sciences, 460 Page Mill Road, Palo Alto, California, 94306.
Department of Biology, University of Rochester, Rochester, New York, 14627.
Evolution. 1996 Dec;50(6):2328-2337. doi: 10.1111/j.1558-5646.1996.tb03620.x.
The Drosophila quinaria group is unusual within the genus in that it comprises both mycophagous and nonmycophagous species. DNA sequence data from three regions of the mitochondrial genome were used to infer relationships among four mycophagous species and three that breed on decaying water plants. Phylogenetic analysis of these species show that breeding in mushrooms and tolerance of high levels of α-amanitin were the ancestral states within the group. Thus, breeding in decaying water plants and intolerance of α-amanitin are derived conditions. We also found that the D. quinaria species group does not comprise separate mycophagous and nonmycophagous clades, but rather that (1) the shift from mushrooms to decaying plants occurred on at least two occasions; or (2) mycophagy reevolved within a lineage that had previously shifted to breeding on plants. The correlation between mycophagy and α-amanitin tolerance is perfect across the species we have examined, indicating that there is no detectable time lag between an ecological shift to a new breeding site and correlated changes in biochemical adaptation. The genetic distance between the mycophagous D. recens and the nonmycophagous D. quinaria indicates that these species split only about 1 M.Y.B.P. In terms of α-amanitin tolerance, D. recens and D. quinaria are typical of other ecologically similar species within the group. Thus, evolutionary changes in α-amanitin tolerance can evidently occur on the order of about 1 million yr. Our data also indicate that, in comparison to other groups of Drosophila, the quinaria species group may be undergoing an adaptive radiation.
果蝇类群在果蝇属中很不寻常，因为它既包含食菌物种，也包含非食菌物种。利用线粒体基因组三个区域的DNA序列数据来推断四种食菌物种和三种在腐烂水生植物上繁殖的物种之间的关系。对这些物种的系统发育分析表明，在蘑菇中繁殖和对高浓度α-鹅膏菌素的耐受性是该类群中的原始状态。因此，在腐烂水生植物上繁殖和对α-鹅膏菌素不耐受是衍生状态。我们还发现，拟果蝇物种组并不包含独立的食菌和非食菌进化枝，而是(1)从蘑菇到腐烂植物的转变至少发生了两次；或者(2)食菌习性在一个先前已转向在植物上繁殖的谱系中重新进化。在我们研究的所有物种中，食菌习性与α-鹅膏菌素耐受性之间的相关性是完美的，这表明从生态角度转向新的繁殖地点与生化适应性的相关变化之间没有可检测到的时间滞后。食菌的 recens 果蝇和非食菌的拟果蝇之间的遗传距离表明，这些物种大约在100万年前才分化。就α-鹅膏菌素耐受性而言，recens 果蝇和拟果蝇是该类群中其他生态相似物种的典型代表。因此，α-鹅膏菌素耐受性的进化变化显然可以在大约100万年的时间尺度上发生。我们的数据还表明，与果蝇的其他类群相比，拟果蝇物种组可能正在经历适应性辐射。
