True and false gharials: A nuclear gene phylogeny of crocodylia Journal Article


Author(s): Harshman, John; Huddleston, Christopher J; Bollback, Jonathan P; Parsons, Thomas J; Braun, Michael J
Article Title: True and false gharials: A nuclear gene phylogeny of crocodylia
Affiliation
Abstract: The phylogeny of Crocodylia offers an unusual twist on the usual molecules versus morphology story. The true gharial (Gavialis gangeticus) and the false gharial (Tomistoma schlegelii), as their common names imply, have appeared in all cladistic morphological analyses as distantly related species, convergent upon a similar morphology. In contrast, all previous molecular studies have shown them to be sister taxa. We present the first phylogenetic study of Crocodylia using a nuclear gene. We cloned and sequenced the c-myc proto-oncogene from Alligator mississippiensis to facilitate primer design and then sequenced an 1,100-base pair fragment that includes both coding and noncoding regions and informative indels for one species in each extant crocodylian genus and six avian outgroups. Phylogenetic analyses using parsimony, maximum likelihood, and Bayesian inference all strongly agreed on the same tree, which is identical to the tree found in previous molecular analyses: Gavialis and Tomistoma are sister taxa and together are the sister group of Crocodylidae. Kishino-Hasegawa tests rejected the morphological tree in favor of the molecular tree. We excluded long-branch attraction and variation in base composition among taxa as explanations for this topology. To explore the causes of discrepancy between molecular and morphological estimates of crocodylian phylogeny, we examined puzzling features of the morphological data using a priori partitions of the data based on anatomical regions and investigated the effects of different coding schemes for two obvious morphological similarities of the two gharials.
Keywords: Animals; Likelihood Functions; Molecular Sequence Data; Phylogeny; Base Sequence; Base Composition; Bayes Theorem; Data Interpretation, Statistical; Genes, myc/genetics; Alligators and Crocodiles/anatomy & histology/classification/genetics
Journal Title: Systematic Biology
Volume: 52
Issue 3
ISSN: 1063-5157
Publisher: Oxford University Press  
Publication Place: England
Date Published: 2003-01-01
Start Page: 386
End Page: 402
Language: eng
DOI: 10.1080/10635150390197028
Open access: no