Abstract
The activity patterns of two closely related echimyid rodents (spiny rats) of the Brazilian Caatinga were studied. One species, Proechimys [Trinomys] yonenagae, is a fossorial dweller of fixed sand dunes. P. [T.] albispinus, inhabits remnants of the Atlantic rainforest areas. A third species, Trichomys apereoides, collected in granite formations in the Caatinga was also studied. The animals were kept individually in cages under controlled conditions and light-dark cycle of 12:12 h. Data were collect by Scan sampling every 2 h, over 3 days, and were analyzed by Cosinor method. All species were nocturnal. P. yonenagae showed a regular pattern of circadian activity and restricted its activity to subjective night. P. albispinus showed an intermittent pattern of activity, especially in the dark phase. T. apereoides showed a bimodal pattern with high crepuscular peaks of activity. A high level of synchrony was found in the activity among individual P. yonenagae. No sex differences were found in behavioral patterns of either P. yonenagae or P. albispinus. Since the two species of Proechimys share a common ancestor, the differences that were found stress the importance of external selection over circadian rhythmicity.
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