© 2005 Society of Systematic Biologists
Exploring Rate Variation Among and Within Sites in a Densely Sampled Tree: Species Level Phylogenetics of North American Tiger Beetles (Genus Cicindela)
1 Department of Entomology, The Natural History Museum London SW7 5BD, United Kingdom E-mail: a.vogler{at}nhm.ac.uk
2 Department of Biological Sciences, Imperial College London Silwood Park Campus, Ascot, Berkshire SL5 7PY, United Kingdom
3 Faculdade de Ciências da Universidade de Lisboa, Departamento de Biologia Animal, Centro de Biologia Ambiental, Rua Ernesto Vasconcelos 1749–016, Campo Grande, Lisboa, Portugal
4 Jodrell Laboratory, Royal Botanic Gardens Kew TW9 3DS, United Kingdom
Edited by Ziheng Yang: Assiciate Editor
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Abstract |
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Species-level phylogenetic studies require fast-evolving nucleotide positions to resolve relationships among close relatives, but these sites may be highly homoplastic and perhaps uninformative or even misleading deeper in the tree. Here we describe a species-level analysis of tiger beetles in the genus Cicindela (Coleoptera: Cicindelidae) for 132 terminal taxa and 1897 nucleotide positions from three regions of mtDNA, comprising 75% coverage of species occurring in North America. Evenly weighted parsimony analysis recovered four major clades representing radiations confined to North and Central America. Relationships near the tips were well supported but signal was contradictory at deeper nodes. Two major categories (3rd positions and all others) can be distinguished in likelihood analysis of character variation, of which only the fast-changing 3rd position characters were affected by saturation. However, their downweighting under a variety of criteria did not improve the tree topology at basal nodes. There was weak conflict between 3rd and non-3rd position characters deep in the tree, but support levels declined towards the root for all categories, even on trees that were reconstructed from 3rd and non-3rd positions separately. Statistical analysis of parsimony-based character transitions along branches showed a largely homogeneous distribution of change along the root-to-tip axis. The comparison of character transitions among the four major portions of the tree revealed deviations from stochastic distribution for the non-3rd positions, but not for 3rd positions. Hence, variability of functionally constrained non-3rd positions differs between clades and may be dependent on the character states at other sites, consistent with the covarion model of molecular evolution. The results suggest that some properties of 3rd positions are less problematic for phylogenetic reconstruction than other categories despite their high total homoplasy. In densely sampled data sets of closely related species, the disadvantages of weighting schemes according to homoplasy levels outweigh the benefits, showing the difficulty of devising meaningful weighting schemes that are applicable universally throughout the tree.
Keywords: Coleoptera; heterotachy; homoplasy weighting; mtDNA; nodal support; rate variation; saturation; species level phylogenies
Received November 1, 2001; Revised April 5, 2002; Accepted August 17, 2004
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