Siixén-Tullberg Birgitta
Department of Zoology, University of Stockholm, 106 91 Stockholm, Sweden.
Evolution. 1993 Aug;47(4):1182-1191. doi: 10.1111/j.1558-5646.1993.tb02145.x.
In a published paper, a method for testing the correlation between two discrete characters was presented and applied to test whether in butterfly larvae origins of gregariousness are concentrated to lineages with aposematic coloration. The relationship was found to be nonsignificant. However, the butterfly data on which the test was applied had been compiled in another study to investigate evolutionary sequences and was biased, because there was an overrepresentation of aposematic, as compared to cryptic, branches in the sample. In the paper presented here, aposematic and cryptic clades of the original phylogeny were resolved to the same degree, and the resulting set of branches may be regarded as unbiased with respect to the hypothesis being tested. A method for testing the contingency of states in two characters was then applied to the new data set, resulting in a highly significant relationship between origins of gregariousness and aposematic coloration. I argue that when using statistical methods on phylogenetic data, it is crucial to resolve various parts of the phylogeny to the same comparable systematic unit in order not to get a distorted sample of taxa/branches.
在一篇已发表的论文中，提出了一种用于测试两个离散性状之间相关性的方法，并将其应用于检验蝴蝶幼虫的群居起源是否集中于具有警戒色的谱系。结果发现这种关系并不显著。然而，应用该测试所依据的蝴蝶数据是在另一项研究中为调查进化序列而汇编的，并且存在偏差，因为与隐秘色分支相比，样本中警戒色分支的占比过高。在本文中，原始系统发育树中的警戒色和隐秘色分支被解析到相同程度，并且由此产生的分支集对于所测试的假设而言可被视为无偏差的。然后将一种用于测试两个性状状态偶然性的方法应用于新数据集，结果表明群居起源与警戒色之间存在高度显著的关系。我认为，在对系统发育数据使用统计方法时，至关重要的是将系统发育的各个部分解析到相同的可比系统单元，以免获得扭曲的分类群/分支样本。
