Abstract
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.
Highlights
Understanding how morphological variation across individuals arises and how it is distributed both temporally and spatially have attracted the attention of biologists over the years (Verwaijen, Van Damme and Herrel, 2002; Harmon et al, 2003; Kaliontzopoulou, Pinho and Martínez-Freiría, 2018).Size is the predominant axis of morphological variation within and among populations (Rohlf, 1990)
While both ontogenetic and static allometry analyses reflect the major contribution of size variation in shaping body relative dimensions, we found that variation between the sexes and across colour morphs is still significant after size effects are taken into account, pointing to possible evolutionary mechanisms that may underlie intraspecific morphological variability in Vipera seoanei
Our results provide a thorough description of morphological variability in Vipera seoanei, highlighting the relevance of combining different tools and analyses that allow us to weight the contribution of different proximate and evolutionary factors in shaping intraspecific variation
Summary
Understanding how morphological variation across individuals arises and how it is distributed both temporally and spatially have attracted the attention of biologists over the years (Verwaijen, Van Damme and Herrel, 2002; Harmon et al, 2003; Kaliontzopoulou, Pinho and Martínez-Freiría, 2018).Size is the predominant axis of morphological variation within and among populations (Rohlf, 1990). Changes in size and shape occurring during growth and their relationship (i.e. ontogenetic allometry) are of essential importance for investigating the developmental processes producing the structures of interest (McNamara, 2012). Allometric variation across individuals at the same developmental stage within a population (i.e. static allometry) can be informative on the selective processes acting on individuals, since allometric parameters can be directly linked to both ecological adaptation (Gould, 1966). Body structures that are of particular relevance for either resource and/or mate acquisition, frequently tend to be positively allometric both ontogenetically and statically, a pattern which reflects higher investment during growth and a selective advantage for those individuals that possess a larger relative size of such structures, respectively
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