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Chironius carinatus. JCM |
Fourteen colubrid genera are
known from South America: including Chironius Fitzinger, 1826. This is one of
the largest genera, with 16 species known to date. Its distribution ranges from
the northern coast of Honduras to Uruguay and northeastern Argentina; and they
are present in the Lesser Antilles. Chironius are long, slender,
oviparous snakes that are mostly diurnal racers of terrestrial and arboreal
habits. Most species inhabit lowland tropical rainforests, but also include
humid montane forests and open formations. Dixon et al. (1993) made an
extensive revision of Chironius and proposed the first morphological
phylogeny of the genus, based mostly on hemipenial and external morphology.
Their tree topology was not obtained using computer-based techniques, and no
outgroup taxa were included in the study. Nevertheless, they discussed the
affinities of Chironius with the other South American colubrid snakes,
suggesting that Dendrophidion represents the sister-group.
Klaczko and colleagues present a
phylogenetic hypothesis for 14species of the genus Chironius based on a
combined molecular and morphological data matrix that includes one nuclear (c-mos)
and two mitochondrial (12S and 16S) genes, and 37 morphological
characters retrieved from scale, skull, and hemipenial features. They test the monophyly of the
genus and provide additional evidence for its sister-group relationship within
the South American radiation of colubrid snakes.
Phylogenetic relationships were inferred
using maximum parsimony (MP) and maximum likelihood (ML). Their combined
morphological and molecular analyses strongly support the monophyly of the
genus Chironius and its sister-group relationship with a clade formed by
the genera Dendrophidion and Drymobius. Phylogenetic
relationships within the genus Chironius is still controversial,
although five clades are retrieved with medium to strong support.
Their results corroborate three
of the clades suggested by Dixon et al.
(1993) (i.e. C. scurrulus and C. laevicollis; C. bicarinatus and C. flavolineatus; C. foveatus, C. multiventris,
and C. laurenti). But, Dixon et al.
(1993) retrieved the clade formed by C.
scurrulus and C. laevicollis in
the least inclusive position in their tree, whereas the combined analyses of
Klaczko et al. reached the opposite result, with this clade in a basal position
within the genus. Chironius laevicollis
and C. scurrulus form a well-supported
clade that corresponds to the most basal clade within Chironius in the MP combined analysis, and to the second most basal
clade (including C. fuscus as their
sister species) in the ML combined analysis. This clade is supported by seven
unambiguous molecular synapomorphies, by the presence of lobular calyces in the
hemipenis that gradually decrease towards the base of the organ, and by the
absence of a bandeddorsal pattern in juveniles. The clade formed by C. vincenti, C. bicarinatus, and C.
flavolineatus received only very low support values, but is corroborated by
two unambiguous morphological synapomorphies: a Meckelian fossa delimited by
the dentary and the splenial bones, and an anterior extension of the
supratemporal that overlaps the parietal–prootic suture. Chironius bicarinatus and C.
flavolineatus also form a poorly supported clade) defined exclusively by
two unambiguous morphological synapomorphies: presence of apical pits
restricted to the neck; and absence of a medial process in the prefrontal. Chironius laurenti, C. multiventris, and C.
foveatus form a moderately supported clade defined exclusively by eight
molecular unambiguous synapomorphies, whereas C. multiventris + C. foveatu form a clade supported by three
molecular and one morphological synapomorphies.
Relationships with the genus Chironius remain controversial and more
work needs to done on these interesting and widespread snakes.
Citations
Dixon
JR, Wiest JA, Cei JM. 1993. Revision of Neotropical snake genus Chironius
Fitzinger (Serpentes, Colubridae). Monografie XIII. Torino: Museo
Regionale di Scienze Naturali.
Klaczko,
J., Montingelli, G. G., & Zaher, H. (2014). A combined morphological and
molecular phylogeny of the genus Chironius
Fitzinger, 1826 (Serpentes: Colubridae). Zoological Journal of the Linnean Society. doi: 10.1111/zoj.12147.