|Chironius carinatus. JCM|
The Neotropical snakes often referred to sipo snakes belong to the genus Chironius. These are large diurnal snakes with a long tail and big eyes that differ from other Neotropical snakes in having only 10 or 12 dorsal scale rows at midbody. Currently, 22 species range from Central America southward to Uruguay and northeastern Argentina.
Based on the largest geographical sampling to date including ∼90% of all species, Torres-Carvajal et al (2018) analyzed one nuclear and three mitochondrial genes using phylogenetic methods to (1) test the monophyly of Chironius and some of its widely distributed species; (2) identify lineages that could represent undescribed species; and (3) reconstruct ancestral distributions. The authors’ best hypothesis placed C. grandisquamis (Chocoan Rainforest) + C. challenger (Pantepui) as sister to all other species. Based on phylogeny and geographic distribution, we identified 14 subclades as putative species within Chironius fuscus, C. multiventris (including C. foveatus and C. laurenti), C. monticola, and C. exoletus. Under current taxonomy, these species show nearly twice as much genetic diversity as other species of Chironius for ND4. Biogeographical analyses using BioGeoBEARS suggest that current distribution patterns of Chironius species across South America resulted from multiple range expansions. The MRCA of the clade C. challenger + C. grandisquamis was most likely distributed over the Pantepui region, the Andes, and the Chocoan Rainforest, whereas the remaining lineages probably evolved from an Amazonian ancestor.
Torres-Carvajal O, Echevarría LY, Lobos SE, Venegas PJ, Kok PJ. Phylogeny, diversity and biogeography of Neotropical sipo snakes (Serpentes: Colubrinae: Chironius). Molecular phylogenetics and evolution. 2018 Oct 24.