Ecomorphological changes of the mandibles of two living caiman species in the post-hatching ontogeny

FERNANDEZ BLANCO, MARÍA VICTORIA; CASSINI, GUILLERMO HERNÁN; BONA, PAULA

Montpellier

Simposio; Symposium de Morphométrie et Evolution des Formes (SMEF); 2021

Institute of Evolutionary Science of Montpellier

Ontogenetic morphological transformation ofthe mandible of living crocodiles has been poorly studied. We have explored theinter- and intraspecific variation of the mandible in two extant caimanspecies, exploring the relationship between these morphological changes anddiet, from a quantitative approach. We applied three-dimensional geometricmorphometric methods on post-hatching ontogenetic mandibular series of Caiman latirostris and C. yacare. We performed interspecificPrincipal Component Analysis (PCA), and intraspecific Regression and PartialLeast Squares (PLS) analyses using the Morpho package in R software. Only PC1and PC2 were meaningful (explaining the 33.08% and 16.36% of the variance,respectively). Species were segregated along the PC1 with C. yacare located onthe positive values (slender mandibles) and C. latirostris on the negative ones(robust mandibles). Both the PC2 and the regression analyses showed shapechanges along the ontogeny (common and specific pattern, respectively) withjuveniles of both species in the negative values and adults towards positiveones. Allometric scaling explains 19.01% of variation in C. yacare and 22.31% in C.latirostris. The adult mandible is longer, wider and taller than thejuvenile (more conspicuous in C. yacare). The PLS analysis of both speciesshows a significant relationship between ontogenetic shape variation and diet.Although proportions and feeding items are similar in the two caiman species(e.g., adults of both species feed mainly on vertebrates), crustaceans are avery important component of the diet in the juveniles of C. latirostris whereas snails are for C. yacare. Summarizing, common morphological changes occurringduring ontogeny seems to reect the same mechanical requirements for crushingand killing in both species, driven by ontogenetic changes in the diet from invertebratesto vertebrates. Additionally, difierences in the mandible morphology (gracileand robust) could be related to difierent feeding mechanical requirements (stifinessand toughness) and to difierent habitat preferences.