Bromham Lindell, Woolfit Megan
Centre for the Study of Evolution, School of Life Sciences, University of Sussex, Falmer, Brighton, UK.
Syst Biol. 2004 Oct;53(5):758-66. doi: 10.1080/10635150490522278.
The reliability of molecular clocks has been questioned for several key evolutionary radiations on the basis that the clock might run fast in explosive radiations. Molecular date estimates for the radiations of metazoan phyla (the Cambrian explosion) and modern orders of mammals and birds are in many cases twice as old as the palaeontological evidence would suggest. Could some aspect of explosive radiations speed the molecular clock, making molecular date estimates too old? Here we use 19 independent instances of recent explosive radiations of island endemic taxa as a model system for testing the proposed influence of rapid adaptive radiation on the rate of molecular evolution. These radiations are often characterized by many of the potential mechanisms for fast rates in explosive radiations--such as small population size, elevated speciation rate, rapid rate of morphological change, release from previous ecological constraints, and adaptation to new niches--and represent a wide variety of species, islands, and genes. However, we find no evidence of a consistent increase in rates in island taxa compared to their mainland relatives, and therefore find no support for the hypothesis that the molecular clock runs fast in explosive radiations.
分子钟的可靠性在几个关键的进化辐射事件中受到了质疑，原因是在爆发性辐射中分子钟可能走得过快。后生动物门辐射（寒武纪大爆发）以及现代哺乳动物和鸟类目辐射的分子年代估计，在很多情况下是古生物学证据所显示年代的两倍。爆发性辐射的某些方面是否会加快分子钟，从而使分子年代估计偏老呢？在这里，我们将岛屿特有类群近期19次独立的爆发性辐射作为一个模型系统，来检验快速适应性辐射对分子进化速率的假定影响。这些辐射通常具有爆发性辐射中许多导致快速进化速率的潜在机制——比如种群规模小、物种形成速率提高、形态变化速率快、摆脱先前的生态限制以及适应新生态位——并且涵盖了各种各样的物种、岛屿和基因。然而，我们没有发现与大陆近缘物种相比，岛屿类群的进化速率持续增加的证据，因此也没有找到支持分子钟在爆发性辐射中走得过快这一假说的证据。
