Sources of intraspecific morphological variation in Vipera seoanei: allometry, sex, and colour phenotype

Abstract

Snakes frequently exhibit ontogenetic and sexual variation in head dimensions, as well as the occurrence of distinct colour morphotypes which might be fitness-related. In this study, we used linear biometry and geometric morphometrics to investigate intraspecific morphological variation related to allometry and sexual dimorphism in Vipera seoanei, a species that exhibits five colour morphotypes, potentially subjected to distinct ecological pressures. We measured body size (SVL), tail length and head dimensions in 391 specimens, and examined variation in biometric traits with respect to allometry, sex and colour morph. In addition, we analysed head shape variation by recording the position of 29 landmarks in 123 specimens and establishing a low-error protocol for implementing geometric morphometrics to European vipers. All head dimensions exhibited significant allometry, while sexual differences occurred for SVL, relative tail length and snout height. After considering size effects, we found significant differences in body proportions between the sexes and across colour morphs, which suggests an important influence of lowland and montane habitats in shaping morphological variation. By contrast, head shape did not exhibit significant variation across sexes or colour morphs. Instead it was mainly associated to allometric variation, where the supraocular and the rear regions of the head were the areas that varied the most throughout growth and across individuals. Overall, this study provides a thorough description of morphological variability in Vipera seoanei and highlights the relevance of combining different tools (i.e. linear and geometric morphometrics) and analyses to evaluate the relative contribution of different factors in shaping intraspecific variation.

First helminthological data on the Iberian adder, Vipera seoanei

“…4 ). Assuming that sexual maturation occurs at 325 mm of SVL (Lucchini et al 2020 ; Espasandín et al 2022 ), we indicate that helminths were mostly found in adults of V . seoanei .…”

“…seoanei (Espasandín et al 2022 ) and frequently relate to the ecology of the Iberian viper species (e.g. Martínez-Freiría et al 2008 , 2015 ; Lucchini et al 2020 ; Chamorro et al 2021 ). Further information on how they were obtained can be found in Espasandín et al ( 2022 ).…”

First helminthological data on the Iberian adder, Vipera seoanei

“…In reptiles, body length correlates to age due to an undetermined growth throughout their life (Candan 2021). Indeed, assuming 325 mm as SVL at sexual maturation (Lucchini et al 2020;Espasandín et al 2022) we indicate that helminths were mostly found in adults of V. seoanei. This agrees with results from other reptile species in which body length also has a signi cant effect on the occurrence of parasites.…”

Isolation and characterization of polymorphic microsatellite loci for the three Iberian vipers, Vipera aspis, V. latastei and V. seoanei by Illumina MiSeq sequencing

“…However, nuclear markers are needed to address reproductive isolation and the extent of gene flow among divergent lineages, aiding in clarifying their taxonomic status [ 15 ]. Vipera seoanei , on the other hand, exhibits a shallow genetic structure and low genetic diversity at the mtDNA level [ 16 ], that contrasts with its high morphological and colouration polymorphism [ 17 , 18 ]. The use of microsatellite loci has the potential to provide a detailed perspective on the genetic diversity and structure of populations and the factors contributing to their phenotypic variation.…”