Aquatic adaptations in a Neotropical coral snake: A study of morphological convergence

Micrurus surinamensis is an aquatic member of the genus Micrurus. This species is known for its highly specialized venom and distinctive diet, mostly made of aquatic vertebrates. Here, we explore both external (head and body) and skull shape morphologies in M. surinamensis, comparing it with two terrestrial species of the genus (M. lemniscatus and M. spixii) and to aquatic and terrestrial species of distantly related groups. We use both traditional and geometric morphometrics to determine whether the presence of similar traits in head shape morphology is rather the result of adaptive convergences between M. surinamensis and other aquatic species, or whether it is the product of phylogenetic conservatism within the genus. Results from both traditional and geometric morphometrics show that M. surinamensis can be considered convergent with aquatic species, mainly in the skull shape. Micrurus surinamensis differs from the two terrestrial species of Micrurus by having a wider head, smaller distance between nostrils, and a long tail. Geometric morphometric analysis shows that despite having an extremely conserved skull and mandible shape, M. surinamensis shows a longer supratemporal and quadrate bones than in terrestrial Micrurus, indicating a larger gape for this species. A more kinetic skull combined with a larger gape would allow M. surinamensis to feed on fish, which represent larger and wider prey that contrast with the elongate prey, which compose the main diet of species in the genus Micrurus. Our results illustrate the importance of both phylogenetic conservatism and adaptation in shaping species morphology.