Department of Biology, Indiana University, 1001 East Third Street, Bloomington, IN 47405-3700, USA.
Curr Biol. 2009 Sep 15;19(17):1438-41. doi: 10.1016/j.cub.2009.06.062. Epub 2009 Jul 23.
The maintenance of sexual reproduction in natural populations is a pressing question for evolutionary biologists. Under the "Red Queen" hypothesis, coevolving parasites reduce the reproductive advantage of asexual reproduction by adapting to infect clonal genotypes after they become locally common. In addition, the "geographic mosaic" theory of coevolution proposes that structured populations of interacting species can produce selection mosaics manifested as coevolutionary "hot spots" and "cold spots". Here, we tested whether a steep, habitat-specific cline in the frequency of sexual reproduction in a freshwater snail could be explained by the existence of hot spots and cold spots for coevolving parasites. We found that the shallow-water margins of lakes, where sexual reproduction is most common, are coevolutionary hot spots, and that deeper habitats are cold spots. These results are consistent with the geographic mosaic theory, in that the intensity of selection resulting from biological interactions can vary sharply in space. The results also support the Red Queen hypothesis, in that sex is associated with coevolutionary hot spots for virulent parasites.
性繁殖在自然种群中的维持是进化生物学家关注的一个紧迫问题。根据“红皇后假说”，共进化的寄生虫通过适应在无性繁殖变得局部常见后感染克隆基因型，从而降低了无性繁殖的生殖优势。此外，共进化的“地理镶嵌”理论提出，相互作用的物种的结构化种群可以产生选择镶嵌，表现为共进化的“热点”和“冷点”。在这里，我们测试了淡水蜗牛中生殖方式的频率是否存在陡峭的、特定于栖息地的梯度，这是否可以用共进化寄生虫的热点和冷点来解释。我们发现，湖泊浅水区是生殖最常见的地方，是共进化的热点，而更深的栖息地则是冷点。这些结果与地理镶嵌理论一致，即生物相互作用产生的选择强度在空间上可以急剧变化。这些结果也支持了红皇后假说，因为性与毒性寄生虫的共进化热点有关。
