Bite it forward...bite it better? Procumbency and mechanical advantage in the chisel-tooth and scratchdigger genus Ctenomys (Caviomorpha, Rodentia)

BECERRA, FEDERICO; ECHEVERRÍA, ALEJANDRA; BUEZAS, GUIDO; VASSALLO, ALDO IVÁN

Praga

Congreso; Sociedad de Biología Experimental SEB Praga 2015; 2015

Society of Experimental Biology

The subterranean genus Ctenomys (>60 species, ~100~1000 g) constructs its burrowsby using both forefeet and teeth throughout a wide range of habitats in South America.Thes diverse habitat conditions promoted a high variation of incisors? angle of attack(procumbency) accompanying a mostly conservative skull morphology. Skulls of twentyfourctenomyid and four octodontid species were studied looking for interspecific variationin the procumbency, mechanical advantage of the jaw adductor muscles (MAJAM),and the linkage between these two parameters to test previous hypotheses, beyondthe body size effect. The in- and out-lever arms (Li and Lo ) of the adductor muscleswere determined based upon their insertion?s 3D-coordinates and used to calculatetheir mechanical advantage (Li /Lo ). Interspecific scaling relationships for musclesmeasurements were analysed through phylogenetically independent standardizedcontrasts, which did not substantially vary from the original data. RMA regression analysesshowed that the Lo and three muscles? Li exhibited a positive allometry, while the otherfour muscles? Li scaled isometrically with body size. Incisors? procumbency showed a nonsignificantrelationship with body size, and even when it ranged between 84.100-121.90°in ctenomyids and between 79.00а-123.00° in octodontids, GLMs showed that, in general,it was not significantly correlated with MAJAM. This study shows that, contrary to whatit was traditionally believed, incisor?s procumbency variation do not result in a change ofMAJAM. This fact could be explained by a rearrangement of the skull morphology, not onlyby changing the out-lever arm (influenced by procumbency) but also in the in-lever arms(muscle attachment sites).