Wayne R K, Meyer A, Lehman N, Van Valkenburgh B, Kat P W, Fuller T K, Girman D, O'Brien S J
Department of Biology, University of California-Los Angeles 90024.
Proc Natl Acad Sci U S A. 1990 Mar;87(5):1772-6. doi: 10.1073/pnas.87.5.1772.
In discussions about the relative rate of molecular evolution, intraspecific variability in rate is rarely considered. An underlying assumption is that intraspecific sequence differences are small, and thus variations in rate would be difficult to detect or would not affect comparisons among distantly related taxa. However, several studies on mammalian mitochondrial DNA (mtDNA) have revealed considerable intraspecific sequence divergence. In this report, we test for differences in the rate of intraspecific evolution by comparing mtDNA sequences, as inferred from restriction site polymorphisms and direct sequencing, between mtDNA genotypes of the eastern African black-backed jackal, Canis mesomelas elongae, and those of two other sympatric jackal species. Our results are unusual for several reasons. First, mtDNA sequence divergence within several contiguous black-backed jackal populations is large (8.0%). Previous intraspecific studies of terrestrial mammals have generally found values of less than 5% within a single population, with larger divergence values most often occurring among mtDNA genotypes from geographically distant or isolated localities. Second, only 4 mtDNA genotypes were present in our sample of 64 jackals. The large sequence divergence observed among these mtDNA genotypes suggests there should be many more genotypes of intermediate sequence divergence if they had evolved in sympatry. Finally, estimates of the rate of mtDNA sequence evolution differ by approximately 2- to 4-fold among black-backed jackal mtDNA genotypes, thus indicating a substantial heterogeneity in the rate of sequence evolution. The results are difficult to reconcile with ideas of a constant molecular clock based on random fixation of selectively neutral or nearly neutral mtDNA sequence mutations.
在关于分子进化相对速率的讨论中，很少考虑种内速率的变异性。一个潜在的假设是种内序列差异很小，因此速率的变化很难检测到，或者不会影响远缘分类群之间的比较。然而，几项关于哺乳动物线粒体DNA（mtDNA）的研究已经揭示了相当大的种内序列分歧。在本报告中，我们通过比较东非黑背胡狼（Canis mesomelas elongae）的mtDNA基因型与另外两种同域胡狼物种的mtDNA基因型之间的mtDNA序列（根据限制性位点多态性和直接测序推断），来测试种内进化速率的差异。我们的结果在几个方面是不同寻常的。首先，几个相邻的黑背胡狼种群内的mtDNA序列分歧很大（8.0%）。以前对陆生哺乳动物的种内研究通常发现单个种群内的值小于5%，较大的分歧值最常出现在地理上遥远或隔离地区的mtDNA基因型之间。其次，在我们的64只胡狼样本中只存在4种mtDNA基因型。在这些mtDNA基因型之间观察到的大序列分歧表明，如果它们是在同域进化的，应该有更多中间序列分歧的基因型。最后，黑背胡狼mtDNA基因型之间的mtDNA序列进化速率估计相差约2至4倍，因此表明序列进化速率存在显著的异质性。这些结果很难与基于选择性中性或近中性mtDNA序列突变的随机固定的恒定分子钟概念相协调。
