Monday, July 29, 2013

Generic changes likely for some Trinidad Chironius

The long-tailed machete,Chironius septentrionalis
Convergent evolution sometimes covers the tracks of genetic lineages, so species can appear to be very similar but have different ancestors. Such appears to be the case with some of the snakes currently in the genus Chironius.  In Trinidad & Toabgo there are three species of Chironius, Machete savane, C. chironius chironius, the long-tailed machete, C. septentrionalis, and the smooth machete C. surrulus (this species is known from only a few specimens on Trinidad).  The sixteen species in the genus tend to have triangular shaped bodies in cross-section, large eyes, 14 or few scale rows at mid body,  they to to actively forage during the day and feed on frogs and lizards. They range from Central America to southern South America and inhabit some of the Lesser Antilles.

In a new study of squamate relationships Pyron et al. (2013) found Chironius to be polyphyletic, with C, carinatus and C. quadricarinatus forming a clade and with nine other species that were included in the study, forming a second clade. The second clade contains C. septentrionalis and  C. scurrulus.
 Chironius carinatus is the type species for the genus, thus it and quadricarinatus (and what ever other species not included in the study are related to it) will retain the name Chironius. The second however will need a new name, and the oldest name available for the clade will likely be Macrops (= large eyes), a genus established by Wagler in 1830 for Linnaeus' species Coluber saturnius, which is now known as Chironius fuscus.

This result demonstrates how little we actually know about the Neotropical herpetofauna, the prevalence of species that look similar but are genetically distinct, and the problems caused by the polytypic species concept. Sorting out the details of this promises to be challenging because several of the currently recognized species of Chironius have subspecies, including C. carinatus.

Citation
Pyron, RA, Burbrink FT, Wiens JJ. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology 13:93 doi:10.1186/1471-2148-13-93

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