Coyne Jerry A, Elwyn Susannah
Department of Ecology and Evolution, The University of Chicago, 1101 E. 57 Street, Chicago, Illinois 60637, USA.
Evolution. 2006 Feb;60(2):279-91.
The desaturase-2 (desat2) locus of Drosophila melanogaster has two alleles whose frequencies vary geographically: one (the "Z" allele) is found primarily in east Africa and the Caribbean, and the other (the "M" allele) occurs in other parts of the world. It has been suggested that these alleles not only cause sexual isolation between races, but that their distribution reflects differential adaptation to climate: Z alleles are supposedly adapted to tropical conditions and M alleles to temperate ones. This has thus been viewed as a case of reproductive isolation evolving as a pleiotropic byproduct of adaptation. Here we reinvestigate this presumed climatic adaptation, using transgenic lines differing in the nature of their desat2 alleles. We were unable to replicate earlier results showing that carriers of M alleles are uniformly more cold resistant and less starvation resistant than carriers of Z alleles. It is thus doubtful whether the distribution of these alleles reflects natural selection involving climate. Mating studies of transgenic lines show some evidence for sexual isolation due to desat2. However, work on other, wild-type lines, as well as observations on the nature of sexual isolation, suggest that this conclusion--and thus the relationship between this locus and mating discrimination between races of D. melanogaster--may also be doubtful.
黑腹果蝇的去饱和酶-2（desat2）基因座有两个等位基因，其频率在地理上有所不同：一个（“Z”等位基因）主要在东非和加勒比地区发现，另一个（“M”等位基因）出现在世界其他地区。有人提出，这些等位基因不仅导致不同种族之间的性隔离，而且它们的分布反映了对气候的不同适应：Z等位基因被认为适应热带条件，M等位基因适应温带条件。因此，这被视为生殖隔离作为适应的多效性副产品而进化的一个例子。在这里，我们使用desat2等位基因性质不同的转基因品系，重新研究这种假定的气候适应性。我们无法重复早期的结果，即M等位基因携带者比Z等位基因携带者普遍更抗寒且更不耐饥饿。因此，这些等位基因的分布是否反映了涉及气候的自然选择值得怀疑。转基因品系的交配研究显示了一些因desat2导致性隔离的证据。然而，对其他野生型品系的研究以及对性隔离性质的观察表明，这一结论——以及因此该基因座与黑腹果蝇不同种族之间交配歧视的关系——也可能值得怀疑。
