Evolution of brain size in a highly diversifying lineage of subterranean rodent genus Ctenomys (Caviomorpha: Ctenomyidae)

ALDO IVÁN VASSALLO; ALEJANDRA ISABEL ECHEVERRÍA

BRAIN BEHAVIOR AND EVOLUTION

KARGER

Año: 2009 vol. 73 p. 138 - 149

0006-8977

We evaluated brain size evolution in a specialized subterranean mammal, the ctenomyid rodent genus Ctenomys (tuco-tuco) and compared it, within a phylogenetic framework, to other caviomorph rodents differing in body size and modes of life. Whereas brain size in Ctenomys  falls below the regression line obtained for caviomorph rodents, some fossorial species within the sister family Octodontidae, which make use of both above and belowground habitats, have a relatively bigger brain size. Ctenomys has experienced a relatively recent and ?explosive? cladogenesis which yielded ~60 living species differing among them nearly one order of magnitude in body size. Based on the evolutionary lag hypothesis between body vs. brain size evolution, a negative correlation between encephalization quotient and body size would be expected for a group experiencing such a recent diversification in size. This is because a decrease of body size occurring during the emergence of a new species should produce a corresponding greater encephalization and vice versa. In spite of the fact that the allometric coefficient of brain weight vs. body weight for 30 living species of Ctenomys was lower than that obtained for families within Caviomorpha, we failed to find any significant relationship between encephalization and body weight. Finally, the relationship between brain size and metabolisms was assessed for those species of Ctenomys in which metabolic data are available. Brain size evolution in Ctenomys  is discussed regarding sensory capabilities and behavioral attributes associated with the occupation of the subterranean ecological niche.