Bermingham E, Lessios H A
Smithsonian Tropical Research Institute, Balboa, Panama.
Proc Natl Acad Sci U S A. 1993 Apr 1;90(7):2734-8. doi: 10.1073/pnas.90.7.2734.
Acceptance of the rough constancy of rates of molecular evolution, averaged over tens of millions of years, is widely used to date the splitting between taxa. However, for the study of speciation a hypothesis of rough constancy over tens of millions of years is of little use. In order to date the splitting of congeneric species within defined ranges of uncertainty, we need to know the variation of evolutionary rates over shorter periods of time. Such estimates of uncertainty are particularly useful if they apply to techniques of molecular comparisons that lend themselves to the assessment of intraspecific variation. We have measured protein divergence by electrophoresis and mitochondrial DNA differentiation by restriction fragment length polymorphism analysis in three pairs of sea urchin species believed to have resulted from the simultaneous fragmentation of ranges of marine species by the emergence of the Isthmus of Panama, about 3 million years ago. Transisthmian isozyme divergence in these pairs varies by an order of magnitude; mitochondrial DNA divergence, on the other hand, is equivalent in all pairs, suggesting that this molecule, assayed by endonucleases, can provide fairly accurate estimates of times since separation in the 3-million-year range.
接受在数千万年时间跨度内分子进化速率大致恒定这一观点，已被广泛用于确定分类单元之间的分化时间。然而，对于物种形成的研究而言，数千万年大致恒定的假设几乎毫无用处。为了在确定的不确定性范围内确定同属物种的分化时间，我们需要了解较短时间内进化速率的变化情况。如果这些不确定性估计适用于有助于评估种内变异的分子比较技术，那么它们就特别有用。我们通过电泳测量了蛋白质差异，并通过限制性片段长度多态性分析测量了线粒体DNA分化，这三组海胆物种据信是大约300万年前巴拿马地峡的出现导致海洋物种分布范围同时破碎而形成的。这几组跨地峡的同工酶差异相差一个数量级；另一方面，线粒体DNA差异在所有组中都是相同的，这表明通过核酸内切酶检测的这种分子能够为300万年时间范围内的物种分化时间提供相当准确的估计。
