Department of Ecology and Evolutionary Biology, University of Toronto, , Toronto, Ontario, Canada , M5S 3B2, Department of Applied Biological Sciences, Saga University, , Saga 840-8502, Japan.
Proc Biol Sci. 2014 Jan 8;281(1777):20132858. doi: 10.1098/rspb.2013.2858. Print 2014 Feb 22.
Species with broad ecological amplitudes with respect to a key focal resource, niche generalists, should maintain larger and more connected populations than niche specialists, leading to the prediction that nucleotide diversity will be lower and more subdivided in specialists relative to their generalist relatives. This logic describes the specialist-generalist variation hypothesis (SGVH). Some outbreeding species of Caenorhabditis nematodes use a variety of invertebrate dispersal vectors and have high molecular diversity. By contrast, Caenorhabditis japonica lives in a strict association and synchronized life cycle with its dispersal host, the shield bug Parastrachia japonensis, itself a diet specialist. Here, we characterize sequence variation for 20 nuclear loci to investigate how C. japonica's life history shapes nucleotide diversity. We find that C. japonica has more than threefold lower polymorphism than other outbreeding Caenorhabditis species, but that local populations are not genetically disconnected. Coupled with its restricted range, we propose that its specialist host association contributes to a smaller effective population size and lower genetic variation than host generalist Caenorhabditis species with outbreeding reproductive modes. A literature survey of diverse organisms provides broader support for the SGVH. These findings encourage further testing of ecological and evolutionary hypotheses with comparative population genetics in Caenorhabditis and other taxa.
物种在关键焦点资源方面具有广泛的生态幅度，即生态位广化者，应该比生态位特化者维持更大和更连通的种群，这导致了一个预测，即相对于其特化的亲缘种，核苷酸多样性将更低，并且更具分化。这种逻辑描述了特化种-广化种变异假说（SGVH）。一些 Caenorhabditis 线虫的异交物种使用各种无脊椎动物扩散载体，并且具有很高的分子多样性。相比之下，Caenorhabditis japonica 与其扩散宿主，盾蝽 Parastrachia japonensis，严格相关联并具有同步的生命周期，后者本身就是一种饮食特化种。在这里，我们对 20 个核基因座的序列变异进行了特征描述，以研究 C. japonica 的生活史如何塑造核苷酸多样性。我们发现，C. japonica 的多态性比其他异交 Caenorhabditis 物种低三倍以上，但本地种群并未在遗传上断开连接。再加上其有限的分布范围，我们提出，它的特化宿主关联导致了比具有异交繁殖模式的宿主广化 Caenorhabditis 物种更小的有效种群大小和更低的遗传变异。对多种生物的文献调查为 SGVH 提供了更广泛的支持。这些发现鼓励在 Caenorhabditis 和其他分类群中，用比较种群遗传学进一步检验生态和进化假说。
