Pellis, Sergio

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    The development of strain typical defensive patterns in the play fighting of laboratory rats
    (eScholarship Publishing, University of California, 2014) Himmler, Stephanie M.; Lewis, Jena M.; Pellis, Sergio M.
    During play fighting, rats attack and defend the nape, which if contacted is nuzzled with the snout. While all strains of rats use the same suite of defensive tactics to protect the nape, different strains use some tactics more frequently. This study tests two hypotheses for this strain difference: (1) each strain has a preference for using particular tactics and (2) strain differences in defense are a byproduct of strain differences in patterns of nape attack. Juvenile Long-Evans (LE) and Sprague-Dawley (SD) males, raised in same strain quads from shortly after weaning to the early juvenile period (i.e., 24-31 days), were tested with unfamiliar same-strain and different-strain partners (Experiment 1) and LE and SD males raised in mixed LE-SD quads were tested with both familiar (Experiment 2) and unfamiliar same-strain and different-strain partners. If hypothesis (1) were true, they would maintain strain-typical defense patterns irrespective of the strain of the attacking partner, whereas if hypothesis (2) were true, it would vary with the strain of the attacking partner. Hypothesis (1) was supported in the first experiment; all the rats maintained their strain-typical patterns regardless of the partner’s strain. However, Experiments 2 and 3 supported neither hypothesis, as each animal displayed strain-divergent behavior when playing with partners of either strain. Given that in Experiments 2 and 3, subjects were reared in mixed-strain groups, it is possible that, during the early juvenile period, play fighting experiences shape strain-typical patterns of use of defensive tactics.