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

FEDERICO BECERRA; ALEJANDRA ISABEL ECHEVERRÍA; GUIDO NICOLÁS BUEZAS; ALDO IVÁN VASSALLO

Praga

Congreso; ANNUAL MAIN MEETING; 2015

The subterranean genus Ctenomys (>60 species, ~100~1000 g) constructs its burrows by 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 twentyfour ctenomyid and four octodontid species were studied looking for interspecific variation in the procumbency, mechanical advantage of the jaw adductor muscles (MAJAM),and the linkage between these two parameters to test previous hypotheses, beyond the body size effect. The in- and out-lever arms (Li and Lo ) of the adductor muscles were determined based upon their insertion?s 3D-coordinates and used to calculate their mechanical advantage (Li /Lo ). Interspecific scaling relationships for muscles measurements were analysed through phylogenetically independent standardized contrasts, which did not substantially vary from the original data. RMA regression analyses showed that the Lo and three muscles? Li exhibited a positive allometry, while the other four muscles? Li scaled isometrically with body size. Incisors? procumbency showed a nonsignificant relationship 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 what it was traditionally believed, incisor?s procumbency variation do not result in a change of MAJAM. This fact could be explained by a rearrangement of the skull morphology, not only by changing the out-lever arm (influenced by procumbency) but also in the in-lever arms (muscle attachment sites).