Meeting Abstract

39.8  Jan. 6  Does among-population variation in head shape reflect diet diversity in Natrixsnakes? BRECKO, J*; HERREL, A; VAN DAMME, R; University of Antwerp; University of Antwerp; University of Antwerp jonathan.brecko@ua.ac.be

Species of the (semi-) aquatic snake genus Natrix vary considerably in the degree of trophic specialisation. For instance, some populations of the viperine snake (N. maura) feed almost exclusively on fish, while others prey primarily on frogs. In contrast, the dice snake (N. tesselata) is known as an extreme fish specialist. Biomechanical considerations predict a functional trade-off in the ability to prey on fish or frogs: catching fish under water requires a small, streamlined head, whereas swallowing frogs necessitates a large, mobile head. We therefore expected that differences in dietary choice would be reflected in the variation in relative head size and shape. More specifically, we predicted a larger interpopulational variation in (relative) head dimensions in N. maura than in N. tesselata. We measured 14 morphometric characteristics in museum specimens from a large number of populations of both species. We corrected these variables for body size and introduced them into principal component analyses. The scores on the first three principal axes were then examined for inter- and intrapopulational variation. In contrast to our expectation, overall variation in head shape in the fish specialist N. tesselata was comparable to that in the catholic N. maura. Differences in head shape among populations contributed significantly to the overall variation in both species. Surprisingly, the amount of variation explained by interpopulational differences was more important in N. tesselata (40%) than in N. maura (25%). When comparing specimens of N. maura with fish and frogs in their stomachs, the former tend to have longer and narrower heads, with smaller distances between the eyes and the nostrils, and reduced dorsal, ventral, frontal and lateral head surfaces.