Profile of wild Neotropical spiny rats ( Trinomys, Echimyidae) in two behavioral tests

Abstract

The performance of three closely related species of spiny rats was compared in the elevated plus-maze and in the open-field tests. Laboratory rats were also evaluated. It was hypothesized that such tests should reveal differences in anxiety and exploratory profile among the wild species, which differ with respect to habitat, type of social organization and locomotion pattern. No consistent differences were found among the spiny rats, as assessed by conventional parameters, while such differences were detected between the domesticated lines. The social spiny rats ( Trinomys yonenagae), which live in dunes, differed from the solitary sylvan species ( T. iheringi and T. albispinus) in only one index of anxiety (open arms end-exploring). Nevertheless, thigmotaxis in novel environments exists in these spiny rats just as it does in the laboratory rats. During the tests, the sylvan species relied on erratic movements and T. iheringi was the most active species, whereas T. yonenagae employed vigilance and direct escape locomotion. This latter feature may be due to challenges imposed by open environments. Defecation score was reduced for all wild rats: it may represent a predation avoidance response. Concerning ethological measures, T. iheringi presented the highest scores of grooming, in both test situations, and T. albispinus the highest scores of rearing in the open-field. The great within-species variability found in the spiny rats may have concealed anxiety differences among them, despite the ability of both tests to reveal plesiomorphic behavioral characteristics, such as thigmotaxis. Our results also support the use of ethological approach in these tests.