Name: Pinto A

Biodeserts supervisors: F Martínez-Freiría

Co-supervisor: Kaliontzopoulou A

Title: Using Geometric Morphometrics and Geographic Information Systems to assess head shape variation and its geographic structure in Vipera seoanei

Institution: University of Porto

Status: Completed




The head of snakes has a major role in their ecology and usually exhibits morphological variation as a response to natural and sexual selection. Here we aim to describe how head shape varies in the Iberian viper, Vipera seoanei, in relation to growth, sex and colour phenotype and along its geographic distribution. V. seoanei is a European viper almost endemic to Northern Iberian Peninsula, with five colour morphs, but low genetic diversity. We used geometric morphometrics on 147 specimens from its distributional range, representing different ages, sexes and colour morphs. We quantified head shape by digitizing 20 landmarks on the dorsal side of the head. We then superimposed landmark coordinates to remove the effects of location, scale and rotation and to obtain shape variables, based on which we performed standard multivariate analyses to explore patterns of variation. Principal Component Analysis showed that the first component of shape variation (49.47% of total variance) was associated to changes in the posterior region of the head and it represented a contrast between vipers with a short but wide posterior head. Shape variation related to the second principal component (25.77% of total variance) represented a contrast between vipers with a narrow posterior head and a wider snout. MANOVA comparisons yielded no significant differences among sexes or colour morphs. However, head shape was significantly different between vipers of different ages. Head shape varied allometrically with head size, under a common slope in all groups, where head growth was associated to an enlargement of the posterior region of the head and a lateral reduction of the area of the eyes. Then, using geographic information systems, interpolations were performed to investigate whether head size and shape vary geographically, showing no solid geographic structure. This study provides a methodological framework for the implementation of geometric morphometrics for the study of head shape variation in European vipers, which will be useful to explore other sources of variability, such as environmental and ecological factors.