Lee, Justin L., Thompson, Adrian, and Mulcahy, Daniel G. 2016. "Relationships between Numbers of Vertebrae, Scale Counts, and Body Size, with Implications for Taxonomy in Nightsnakes (Genus: Hypsiglena)." Journal of Herpetology, 50, (4) 616–620. https://doi.org/10.1670/15-066.
The relationships between the number of trunk and caudal vertebrae, the number of ventral and subcaudal scales, and snout–vent length (SVL) and tail length were investigated in several species of Hypsiglena, including a few specimens from species contact zones. We confirm the presence of a 1:1 relationship between trunk vertebrae and ventral scales within Hypsiglena (99 specimens total; 50 males; 49 females). We also found a positive relationship between the number of ventral scales and SVL in adult specimens. We did not find a 1:1 relationship between caudal vertebrae and subcaudal scales, but there is a positive relationship between subcaudal scales and tail length. Because there is a positive relationship with the number of ventral scales and SVL, we infer—as general population trends—that snakes with more ventral scales have the capacity to grow to be larger than snakes with fewer ventral scales. Many other environmental factors influence body size, however, and this trend should be used only as a general comparison. Therefore, the number of ventral scales can be used as a proxy for general population trends in body size among species of Hypsiglena, as wide geographic-ranging species may be exposed to large-scale environmental gradients (e.g., lower temperatures at higher latitudes). Ventral and subcaudal scale counts may not be good diagnostic characters for assigning individual specimens to taxonomic groups or for diagnosing taxonomic groups, because species appear to show much overlapping variation. This variation may be good for examining different trends in body size between taxa across geographic landscapes.
