Sexual dimorphism and allometry in malacophagus snakes (Dipsadidae: Dipsadinae).

Sexual dimorphism in snakes is generally described in association with body or tail size and scale counts, with relatively few studies addressing intrasexual divergence in the skull. Here, we analyzed sexual dimorphism in the size and shape of skull and body in three malacophagous dipsadine snakes, Dipsas mikanii, Dipsas neuwiedi and Dipsas turgida, as well as allometric effect on these components. We used linear and geometric analysis to assess: (1) if there is sexual dimorphism in cranial components; (2) if there are differences between the sexes regarding body and tail size, number of ventral and subcaudal scales; (3) whether there is covariation between cranial components and body size; (4) if there are changes in cranial shape associated with increased size; and (5) whether there is an allometric relationship between body and tail size. Our results showed that all three species are dimorphic in cranial shape and size (except D. turgida for cranial size), with females having longer and thinner skulls than males. In the three species, the female skull was negatively allometric, whereas the male skull was isometric. Allometry related to cranial shape was significant only in males of D. turgida, which showed greater snout robustness and eye size associated with enlargement of the skull. Females of D. mikanii and D. neuwiedi were significantly larger than males. Only males of D. neuwiedi showed positive allometry for the tail, while dimorphism related to scale counts followed the pattern found in most snakes, with females having a greater number of ventrals and males subcaudals (except D. neuwiedi in the latter case). Based on our results, we hypothesize that patterns of sexual dimorphism and skull allometry in malacophagous snakes may be explained both by aspects related to diet and reproduction. Meanwhile, patterns associated with body size reflect advantages related to fecundity favoring greater reproductive success of females.

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.

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.

Cranial adaptations for feeding on snails in species of Sibynomorphus (Dipsadidae: Dipsadinae).

Neotropical "goo-eating" dipsadine snakes display a set of morphological and histo-chemical adaptations linked to the capture of their soft-bodied, viscous invertebrate prey. Within this group, species from the genus Sibynomorphus feed chiefly on snails and slugs. Here, we analyzed a series of skull and mandible characters in S. mikanii, S. neuwiedi and S. turgidus using geometric morphometrics, with the aim of assessing morphological adaptations related to slug- and snail-feeding in that genus. We further compared the results with Leptodeira annulata, a species that feeds on vertebrates. To evaluate shape differences of the skull and mandible between species we performed a multivariate analysis of variance and a linear discriminant analysis. Our results show that the narrow, elongate skull in S. mikanii may help with slug ingestion, while asymmetry in teeth number and mandibular shape in S. neuwiedi and S. turgidus are likely related to snail feeding.

Cranial adaptations for feeding on snails in species of Sibynomorphus (Dipsadidae: Dipsadinae)

Neotropical "goo-eating" dipsadine snakes display a set of morphological and histo-chemical adaptations linked to the capture of their soft-bodied, viscous invertebrate prey. Within this group, species from the genus Sibynomorphus feed chiefly on snails and slugs. Here, we analyzed a series of skull and mandible characters in S. mikanii, S. neuwiedi and S. turgidus using geometric morphometrics, with the aim of assessing morphological adaptations related to slug- and snail-feeding in that genus. We further compared the results with Leptodeira annulata, a species that feeds on vertebrates. To evaluate shape differences of the skull and mandible between species we performed a multivariate analysis of variance and a linear discriminant analysis. Our results show that the narrow, elongate skull in S. mikanii may help with slug ingestion, while asymmetry in teeth number and mandibular shape in S. neuwiedi and S. turgidus are likely related to snail feeding.