Ahmed-Braimah Yasir H, Sweigart Andrea L
Department of Biology, University of Rochester, Rochester, New York 14627
Department of Genetics, University of Georgia, Athens, Georgia 30602.
Genetics. 2015 May;200(1):331-42. doi: 10.1534/genetics.115.174920. Epub 2015 Mar 13.
The genetic basis of species differences remains understudied. Studies in insects have contributed significantly to our understanding of morphological evolution. Pigmentation traits in particular have received a great deal of attention and several genes in the insect pigmentation pathway have been implicated in inter- and intraspecific differences. Nonetheless, much remains unknown about many of the genes in this pathway and their potential role in understudied taxa. Here we genetically analyze the puparium color difference between members of the virilis group of Drosophila. The puparium of Drosophila virilis is black, while those of D. americana, D. novamexicana, and D. lummei are brown. We used a series of backcross hybrid populations between D. americana and D. virilis to map the genomic interval responsible for the difference between this species pair. First, we show that the pupal case color difference is caused by a single Mendelizing factor, which we ultimately map to an ∼11-kb region on chromosome 5. The mapped interval includes only the first exon and regulatory region(s) of the dopamine N-acetyltransferase gene (Dat). This gene encodes an enzyme that is known to play a part in the insect pigmentation pathway. Second, we show that this gene is highly expressed at the onset of pupation in light brown taxa (D. americana and D. novamexicana) relative to D. virilis, but not in the dark brown D. lummei. Finally, we examine the role of Dat in adult pigmentation between D. americana (heavily melanized) and D. novamexicana (lightly melanized) and find no discernible effect of this gene in adults. Our results demonstrate that a single gene is entirely or almost entirely responsible for a morphological difference between species.
物种差异的遗传基础仍未得到充分研究。昆虫研究对我们理解形态进化做出了重大贡献。特别是色素沉着性状受到了大量关注，昆虫色素沉着途径中的几个基因与种间和种内差异有关。尽管如此，关于该途径中的许多基因及其在研究不足的分类群中的潜在作用，仍有许多未知之处。在这里，我们对果蝇属粗壮果蝇组成员之间的蛹壳颜色差异进行了遗传分析。粗壮果蝇的蛹壳是黑色的，而美洲果蝇、新墨西哥果蝇和鲁氏果蝇的蛹壳是棕色的。我们利用美洲果蝇和粗壮果蝇之间的一系列回交杂交群体，绘制了导致这两个物种之间差异的基因组区间。首先，我们表明蛹壳颜色差异是由一个单一的孟德尔因子引起的，我们最终将其定位到5号染色体上一个约11kb的区域。定位区间仅包括多巴胺N-乙酰转移酶基因（Dat）的第一个外显子和调控区域。该基因编码一种已知在昆虫色素沉着途径中起作用的酶。其次，我们表明，相对于粗壮果蝇，该基因在浅棕色分类群（美洲果蝇和新墨西哥果蝇）化蛹开始时高度表达，但在深棕色的鲁氏果蝇中不表达。最后，我们研究了Dat在美洲果蝇（黑色素沉着严重）和新墨西哥果蝇（黑色素沉着较轻）成虫色素沉着中的作用，发现该基因在成虫中没有明显影响。我们的结果表明，一个单一基因完全或几乎完全导致了物种之间的形态差异。
