Department of Zoology, Stockholm University, Stockholm, Sweden.
PLoS One. 2011 Jan 5;6(1):e16057. doi: 10.1371/journal.pone.0016057.
The "oscillation hypothesis" has been proposed as a general explanation for the exceptional diversification of herbivorous insect species. The hypothesis states that speciation rates are elevated through repeated correlated changes--oscillations--in degree of host plant specificity and geographic range. The aim of this study is to test one of the predictions from the oscillation hypothesis: a positive correlation between diet breadth (number of host plants used) and geographic range size, using the globally distributed butterfly subfamily Nymphalinae. Data on diet breadth and global geographic range were collected for 182 Nymphalinae butterflies species and the size of the geographic range was measured using a GIS. We tested both diet breadth and geographic range size for phylogenetic signal to see if species are independent of each other with respect to these characters. As this test gave inconclusive results, data was analysed both using cross-species comparisons and taking phylogeny into account using generalised estimating equations as applied in the APE package in R. Irrespective of which method was used, we found a significant positive correlation between diet breadth and geographic range size. These results are consistent for two different measures of diet breadth and removal of outliers. We conclude that the global range sizes of Nymphalinae butterflies are correlated to diet breadth. That is, butterflies that feed on a large number of host plants tend to have larger geographic ranges than do butterflies that feed on fewer plants. These results lend support for an important step in the oscillation hypothesis of plant-driven diversification, in that it can provide the necessary fuel for future population fragmentation and speciation.
“振荡假说”被提出作为解释食草昆虫物种异常多样化的一般理论。该假说指出，通过宿主植物特异性和地理范围的重复相关变化——振荡——来提高物种形成率。本研究的目的是检验振荡假说的一个预测：使用全球分布的蝴蝶亚科 Nymphalinae，检验饮食广度（使用的宿主植物数量）和地理范围大小之间的正相关性。我们收集了 182 种 Nymphalinae 蝴蝶的饮食广度和全球地理范围数据，并使用 GIS 测量地理范围的大小。我们测试了饮食广度和地理范围大小是否具有系统发育信号，以了解这些特征是否与物种彼此独立。由于该测试结果不确定，因此我们使用了跨物种比较以及使用广义估计方程（在 R 中的 APE 包中应用）考虑系统发育的方法进行了数据分析。无论使用哪种方法，我们都发现饮食广度和地理范围大小之间存在显著的正相关关系。这些结果对于两种不同的饮食广度衡量标准和去除异常值都是一致的。我们得出结论，Nymphalinae 蝴蝶的全球范围大小与饮食广度相关。也就是说，吃大量宿主植物的蝴蝶比吃较少植物的蝴蝶具有更大的地理范围。这些结果为植物驱动的多样化的振荡假说中的一个重要步骤提供了支持，因为它可以为未来的种群分裂和物种形成提供必要的燃料。
