Jordal Bjarte H, Hewitt Godfrey M
School of Biological Sciences, University of East Anglia, Norwich, UK.
Syst Biol. 2004 Oct;53(5):711-34. doi: 10.1080/10635150490468710.
Species-level phylogenies derived from many independent character sources and wide geographical sampling provide a powerful tool in assessing the importance of various factors associated with cladogenesis. In this study, we explore the relative importance of insular isolation and host plant switching in the diversification of a group of bark beetles (Curculionidae: Scolytinae) feeding and breeding in woody Euphor biaspurges. All species in the genus Aphanarthrumare each associated with only one species group of Euphorbia(succulents or one of three different arborescent groups), and the majority of species are endemic to one or several of the Macaronesian Islands. Hence, putative mechanisms of speciation could be assessed by identifying pairs of sister species in a phylogenetic analysis. We used DNA sequences from two nuclear and two mitochondrial genes, and morphological characters, to reconstruct the genealogical relationships among 92 individuals of 25 species and subspecies of Aphanarthrumand related genera. A stable tree topology was highly dependent on multiple character sources, but much less so on wide population sampling. However, multiple samples per species demonstrated one case of species paraphyly, as well as deep coalescence among three putative subspecies pairs. The phylogenetic analyses consistently placed the arborescent breeding and West African--Lanzarote-distributed species A. armatumin the most basal position in Aphanarthrum, rendering this genus paraphyletic with respect to Coleobothrus. Two major radiations followed, one predominantly African lineage of succulent feeding species, and one island radiation associated with arborescent host plants. Sister comparisons showed that most recent divergences occurred in allopatry on closely related hosts, with subsequent expansions obscuring more ancient events. Only 6 out of 24 cladogenetic events were associated with host switching, rendering geographical factors more important in recent diversification.
源自许多独立性状来源和广泛地理采样的物种水平系统发育为评估与分支形成相关的各种因素的重要性提供了一个强大的工具。在本研究中，我们探讨了岛屿隔离和寄主植物转换在一组以木本大戟科肉质植物为食并在其中繁殖的小蠹虫（象甲科：小蠹亚科）多样化过程中的相对重要性。Aphanarthrum属的所有物种分别仅与大戟属的一个物种组（多肉植物或三个不同乔木组之一）相关联，并且大多数物种是马卡罗尼西亚群岛中一个或几个岛屿的特有物种。因此，可以通过在系统发育分析中识别姐妹物种对来评估推测的物种形成机制。我们使用来自两个核基因和两个线粒体基因的DNA序列以及形态特征，来重建Aphanarthrum属及其相关属的25个物种和亚种的92个个体之间的谱系关系。稳定的树形拓扑高度依赖于多个性状来源，但对广泛的种群采样依赖程度要小得多。然而，每个物种的多个样本显示出一个物种并系的情况，以及三对推测的亚种对之间的深度合并。系统发育分析一致将在乔木上繁殖且分布于西非和兰萨罗特岛的物种A. armata置于Aphanarthrum属最基部的位置，使得该属相对于Coleobothrus属成为并系。随后出现了两次主要的辐射，一次是主要以多肉植物为食的非洲谱系，另一次是与乔木寄主植物相关的岛屿辐射。姐妹比较表明，最近的分歧发生在亲缘关系密切的寄主上的异域环境中，随后的扩张掩盖了更古老的事件。在24个分支形成事件中，只有6个与寄主转换相关，这表明地理因素在最近的多样化过程中更为重要。
