Ontogenetic trajectories and sexual dimorphism of a neotropical ground snake genus Erythrolamprus (Serpentes: Dipsadidae)

Abstract

Allometry and sexual dimorphism are potential sources of intraspecific morphological variation. Advances in the methodological framework of geometric morphometrics allow in-depth analysis of these issues, enabling the descriptions and comparisons between groups of multivariate phenotypic attributes and the visualization of allometric trajectories. In the present study, we evaluated the presence of secondary sexual dimorphism in Erythrolamprus miliaris merremi, a semi-aquatic snake occurring in the Atlantic Forest of southeastern Brazil. We assessed linear body measurements and digitized landmarks in the dorsal view of the head of 107 specimens grouped into four categories combining ontogenetic stages and sex. We performed linear models and principal component analyses to estimate and visualize head shape variation and the allometric trajectories of these categories. Adults from both sexes and immature females showed significant static allometry, while immature males showed isometric growth. Although we recovered no sexual dimorphism for head shape, ontogenetic trajectories of both sexes are distinct, with females showing head shape variation throughout ontogenetic development, while males exhibited more conspicuous changes only after sexual maturity. Comparisons with literature data suggest a high degree of variation in ontogenetic allometry of snakes, depending on the phylogenetic group or structure (head/skull) analyzed, while the results for static allometry are more similar between the studied taxa. Only the collection of data on distinct groups of snakes will provide more clues as to whether there is any allometric pattern to these structures, and which factors (evolutionary, ecological or both) are prevalent over it, especially for ontogenetic allometry.