Geographic variation in the long-nosed snake, Rhinocheilus lecontei (Colubridae): beyond the subspecies debate

Abstract

Scalation, colour pattern, linear and geometric morphometrics were used to quantify geographical differentiation in the long-nosed snake, Rhinocheilus lecontei, and to test the hypothesis that all four subspecies are morphologically distinct. Also investigated were potential associations between morphological (scalation, colour pattern, linear measurements) and environmental variables (climate, vegetation, soil). Sexual dimorphism was weakest for geometric and strongest for linear morphometric variables. Morphological variables differed widely in their ability to differentiate subspecies. Linear morphometric variables achieved the most statistically significant pairwise Mahalanobis distances between subspecies, while geometric morphometrics largely failed to differentiate them. Colour pattern showed the strongest and linear morphometrics the weakest correlation with environment. Several characters varied continuously along latitudinal or longitudinal gradients, such that, in some cases, the clines for closely related traits were discordant. No one subspecies was consistently divergent in all analyses, leading to the conclusion that the three mainland subspecies are not sufficiently distinct to warrant separate subspecies status. The island subspecies, though not always statistically distinct, is geographically separate from other populations and differs in characters related to size. Given the small number of specimens available, a decision regarding its taxonomic status (i.e. elevation to species level) is best deferred until additional specimens can be examined and data on molecular variation can be analysed.

Geometric morphometrics in herpetology: modern tools for enhancing the study of morphological variation in amphibians and reptiles

“…A different pattern is observed in snakes, although the reduced number of studies once again hinders the extraction of definite conclusions. The available studies indicate that head/skull shape SD in snakes is non-existent or of relatively low importance, at least as compared to other sources of variation, such as geographic locality (MAnIEr, 2004;SMITH & coLLyEr, 2008) or phylogenetic signal (GEnTILLI et al, 2009). clearly, patterns of shape SD and its variation in turtles and snakes needs to be further investigated in the future.…”

Multivariate and geometric morphometrics in the analysis of sexual dimorphism variation in Podarcis lizards

“…Although the application of geometric morphometrics in SD studies still needs to be explored, some authors report interesting SD patterns revealed by the application of such techniques in various animal taxa (Hood, 2000;Rosas and Bastir, 2002;Loy et al, 2004;Rufino et al, 2004;Valenzuela et al, 2004;Bruner et al, 2005). Until the present, geometric methods have not been extensively applied to study the external morphology of lizards, and very few authors have applied such methods in reptiles (Monteiro et al, 1997;Claude et al, 2003;Marugá n-Lobón and Buscalioni, 2003;Manier, 2004;Bruner et al, 2005;Stayton, 2005;Vidal et al, 2005). In the case of lacertid lizards, geometric morphometrics could be of great use, since SD patterns in this group involve sexual variation in head dimensions and shape.…”

Variación geográfica en Phrynosoma orbiculare (Sauria: Phrynosomatidae): análisis de las subespecies

“…6). A pesar de que con los dos métodos morfométricos, tradicionales y geométricos, no es posible hacer comparaciones directas (Manier 2004) sí es posible realizar algunas relaciones. Por ejemplo, el ancho y largo de la cabeza en el análisis de CP de medidas lineales es el caracter que presenta mayor peso y, con la placa fina de deformación resultante de la configuración de landmarks, se puede apreciar que, la variación se encuentra relacionada con este carácter; como se refiere a continuación para cada una de las poblaciones que mostraron diferencias significativas.…”

“…(Manier 2004). Un primer paso es evaluar los caracteres diagnósticos de las subespecies existentes, para ello se han utilizado diversos métodos que permiten evaluar desde otra perspectiva los caracteres morfológicos diagnósticos.…”

“…Algunos de ellos están circunscritos en la morfometría lineal y otros en la morfometría geométrica, ambas en combinación con la estadística multivariada (Smith 1997). Estos análisis permiten, de acuerdo con algunos autores, redefinir subespecies o asignar nuevos individuos a un grupo subespecífico; pero además, algunos de ellos sugieren cambios en el nivel de clasificación taxonómica de los organismos, es decir, elevar las subespecies a la categoría de especie (Manier 2004, Montanucci 2004, Rastegar-Pouyani 2005, Bastos-Silveria 2007.…”