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

沃伦G.亚伯拉罕森& m .尤班克斯当地理屏障将现有物种划分为两个或两个以上孤立的种群时，新物种就产生了。当山脉、海洋或其他障碍阻止孤立种群之间的繁殖时，每个种群都可以沿着独立的道路进化。如果地理隔离持续的时间足够长，种群可能分化得如此之大，以至于杂交不再可能——一个物种分裂成几个。对于像食草昆虫这样的寄生虫，基因交流的障碍可能不是来自地理，而是来自行为。当交配只发生在寄主植物上时，一贯选择一个寄主的亚种群将不会与选择另一个寄主的亚种群交配。因此，当两个亚种群是同域的，在没有地理分离的情况下，物种形成也会发生。许多人认为同域物种形成的条件限制太大，因此它并不重要。我们在黄花植物上诱导瘿虫的广泛研究和对茎和瘿虫的初步研究表明，寄主选择可能是遗传交换的障碍。我们将研究一种与美国东部两种菊科植物有关的普通翻滚花甲虫的寄主转移和潜在寄主种的形成。我们的研究系统的独特之处在于，一种食草昆虫的宿主转移和随后的宿主种族形成可能直接导致第二种不相关物种的宿主转移和宿主种族形成。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.