One Host Shift Leads to Another: Formation of Host Races in a Gall- and Stem-Boring Beetle

Deb-9806339沃伦·G·亚伯拉罕森和米奇·尤班克斯当地理屏障将现有物种划分为两个或更多孤立的种群时，新物种就会出现。当山脉、海洋或其他障碍阻碍了孤立种群之间的繁殖时，每一个种群都可以沿着一条独立的路径进化。如果地理隔离持续足够长的时间，种群的分化可能会如此之大，以至于不再可能进行杂交--一个物种分裂成几个物种。对于食草性昆虫等寄生虫，基因交换的障碍可能不是来自地理，而是行为。当只在寄主植物上发生交配时，持续选择一种寄主的亚种群不会与选择另一种寄主的亚种群交配。因此，当两个亚群共处时，物种形成可以在没有地理分离的情况下发生。许多人争辩说，共域物种形成的条件过于严格，以至于它不重要。我们对在黄杆植物上诱导虫害的苍蝇的广泛研究，以及我们对茎和虫害甲虫的初步工作表明，寄主选择可能是遗传交流的障碍。我们将研究一种常见的翻滚花甲虫在美国东部的寄主转移和潜在的寄主小种形成。我们的研究系统是独特的，因为一种草食昆虫的宿主转移和随后的宿主小种形成可能直接导致了第二个无关物种的宿主转移和宿主小种形成。鉴于近一半的动物物种是寄生虫，同域物种形成可能是地球生物多样性的一个重要来源。

DEB-9806339 Warren G. Abrahamson & Micky Eubanks New species are known to arise when geographic barriers divide an existing species into two or more isolated populations. When mountains, oceans, or other barriers prevent reproduction between the isolated populations, each can evolve along an independent path. If geographic isolation lasts long enough, the populations may diverge so much that interbreeding is no longer possible -- one species divides into several. With parasites such as herbivorous insects, barriers to genetic exchange may arise not out of geography, but out of behavior. When mating occurs only on the host plant, a subpopulation consistently choosing one host will not mate with that choosing the other. Thus, speciation can occur in the absence of geographic separation when the two subpopulations are sympatric. Many have argued that the conditions for sympatric speciation are too restrictive for it to be important. Our extensive work on flies that induce galls on goldenrod plants and our preliminary work with a stem and gall-boring beetle indicate that host choice can be a barrier to genetic exchange. We will study a host shift and potential host-race formation by a common tumbling flower beetle associated with two species of goldenrod in the eastern United States. Our study system is unique in that a host shift and subsequent host-race formation by one herbivorous insect may have directly contributed to the host shift and host-race formation of a second, unrelated species. Given that nearly half of animal species are parasites, sympatric speciation may be an important source of the earth's biodiversity.