Phylogenetic Relationships of North American Garter Snakes (Thamnophis) Based on Four Mitochondrial Genes: How Much DNA Sequence Is Enough?

Authors: de Queiroz A.¹; Lawson R.²; Lemos-Espinal J.A.³

Source: Molecular Phylogenetics and Evolution, Volume 22, Number 2, February 2002 , pp. 315-329(15)

Publisher: Academic Press

Abstract:

The clade of garter snakes (Thamnophis) includes some of the most abundant and well-studied snakes in North America. However, phylogenetic relationships within this group have been little studied. We used DNA sequences of four mitochondrial genes (cytochrome b and NADH dehydrogenase subunits 1, 2, and 4) to estimate relationships among 29 of the 31 recognized species of Thamnophis plus the related species Adelophis foxi. Both maximum parsimony (MP) and maximum-likelihood (ML) analyses of all these genes combined produced well-resolved trees with moderate (70–89%) to strong (90–100%) bootstrap support for most clades. MP and ML trees were very similar, with no strongly supported conflict between the two analyses. These analyses identify a clade of 12 species largely restricted to México (the “Mexican clade”), and a clade containing 15 species that collectively range from Central America to southern Canada (the “widespread clade”). These two groups are identified as sister taxa in both MP and ML analyses. A clade consisting of the ribbon snakes (T. sauritus and T. proximus) and the common garter snake (T. sirtalis) is placed as the sister group to all other Thamnophis (i.e., the Mexican + widespread clades) in our analyses. High bootstrap proportions at several levels in the tree support the inclusion of both Thamnophis validus, which has traditionally been placed in the genus Nerodia, and the poorly known species Adelophis foxi within Thamnophis. We used randomly sampled characters (i.e., standard bootstrapping) and randomly sampled contiguous blocks of characters to examine the effect of number of characters on resolution of and support for relationships within Thamnophis using MP. In general, these analyses indicate that we have reached a point of strongly diminishing returns with respect to the effect of adding mtDNA sequence characters for the current set of taxa; our sample of 3809 mtDNA characters is apparently “enough.” The next steps to improve the phylogenetic estimate may be to add nuclear DNA sequences, morphology, or behavior, or to sequence additional mtDNA lineages within species. ©2002 Elsevier Science (USA).

Keywords: Adelophis foxi; biogeography; Isthmus of Tehuantepec; Mé; xico; mitochondrial DNA; number of characters; phylogeny; snakes; Thamnophiini; Thamnophis

Language: English

Document Type: Research article

Affiliations: 1: Department of Environmental, University of Colorado, Boulder, Colorado, 80309-0334 2: Osher Foundation Laboratory for Molecular Systematics and Department of Herpetology, California Academy of Sciences, Golden Gate Park, San Francisco, California, 94118 3: Laboratorio de Ecología—UBIPRO, Escuela Nacional de Estudios Profesionales Iztacala, Los Reyes Iztacala, Estado de México, 54090, México

Publication date: 2002-02-01

• In this: publication
• By this: publisher
• In this Subject: Biology
• By this author: de Queiroz A. ;  Lawson R. ;  Lemos-Espinal J.A.

Website © Publishing Technology. Article copyright remains with the publisher, society or author(s) as specified within the article.

• Terms and conditions
• Privacy policy
• Information for advertisers