Nadler S A, Hudspeth D S
Department of Nematology, University of California, Davis, California, 95616-8668,
Mol Phylogenet Evol. 1998 Oct;10(2):221-36. doi: 10.1006/mpev.1998.0514.
Nematodes of the superfamily Ascaridoidea are parasites of the alimentary tract of vertebrates and include species that are of medical and economic importance. Existing evolutionary hypotheses for these organisms have frequently been based on interpretation of one or few "key" structural or life history features. We used nuclear-encoded small (1764 characters) and large subunit (757 characters) ribosomal DNA sequences to estimate the phylogeny of representative taxa from this superfamily. Trees inferred by maximum parsimony and maximum likelihood methods strongly support clades that are primarily consistent with one recent classification of the group. In contrast, most previously proposed phylogenetic hypotheses were significantly worse when compared to the maximum likelihood tree by a statistical method. Hypotheses for the evolution of morphological and life history characters were explored by parsimony mapping these features on several tree topologies, including optimal molecular trees and alternative topologies reflecting traditional expectations deemed not worse in statistical tests. The results identify some consistent putative shared-derived morphological features, but also strongly suggest that some key features emphasized by previous workers represent ancestral states or highly homoplastic characters.
蛔总科的线虫是脊椎动物消化道的寄生虫，包括具有医学和经济重要性的物种。关于这些生物的现有进化假说常常基于对一个或几个“关键”结构或生活史特征的解释。我们使用核编码的小亚基（1764个字符）和大亚基（757个字符）核糖体DNA序列来估计该总科代表性分类单元的系统发育。通过最大简约法和最大似然法推断的树强烈支持主要与该类群最近的一种分类一致的进化枝。相比之下，通过一种统计方法将大多数先前提出的系统发育假说与最大似然树进行比较时，它们明显更差。通过将形态和生活史特征简约映射到几种树形拓扑结构上，包括最优分子树和反映在统计检验中被认为不差的传统预期的替代拓扑结构，探索了形态和生活史特征的进化假说。结果确定了一些一致的假定共同衍生形态特征，但也强烈表明先前研究人员强调的一些关键特征代表祖先状态或高度同源的特征。
