CONICET | Buscador de Institutos y Recursos Humanos

We studied the social interactions between Akodon ararae and Calomys laucha, and between A. azarae and Oligoryzomysjlavescens, by means of experimental confrontations under laboratory conditions. Trials were carried out after two treatments: in the first one ('food' treatment), the animals were offered food ad libitum permanently, whereas in the other ('fast' treatment), the animals were previously submitted to fasting for 30 hours. The largest species- A. ararae - dominated the other two species, being dominant in 69.6% of the aggressive interactions in which a clear dominant/subordinate relationship was detected ( = 79). During the 'fast' treatment, A. azarae fed longer than C. laucha and Ov flauescens, and it was the only species which significantly increased its feeding time with respect to 'food' treatment. There were higher frequencies of aggressive interactions in A. azarae - C. laucha trials than in A. ararae - O. flaoescens trials. Comparisons of the behavioural variables between C. laucha and O. flauescens during their respective confrontations with A. ararae showed that C. laucha had significantly higher median values of freezing and walking behaviours, whereas O.jlavescens showed a higher frequency of alertness. Species differences found in the laboratory support the interpretation that A. azarae is usually dominant over C. laucha and O. jlavescens, and that A. ararae has the priority of access to food sources in situations of food shortage (winter) by means of its social dominance over the other two species. We suggest that the differences in the behavioural reactions of the subordinate species when meeting the dominant one may help to explain the different scales of spatial segregation that C. laucha and O.jlavescens maintain with A. ararae in the field.

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