Object Permanence Cognitive Task Solution Using Wild Rodents

The understanding of the object permanence rule (the notion that an object that has disappeared from view continues to exist) is an important issue for animal cognition studies. This ability has been tested in laboratory rodents, but no studies have been conducted using wild rodent species. The aim of this study was to compare the ability to use the object permanence rule in three species of wild rodents and to identify plausible interspecific behavioral differences. The wood mouse (Sylvaemus uralensis), the striped field mouse (Apodemus agrarius), and the bank vole (Clethrionomys glareolus) were used as subjects in the puzzle-box, in which an animal is motivated to escape from a brightly lit environment into the darkness. Test stages 2, 3 and 4 required an understanding that the underpass which leads from light into the dark part of a box still exists, although it is not seen any longer. The test difficulty gradually increased: at first, the passage to the dark was unobstructed; then, it was covered with sawdust; and, finally, it was blocked using a cardboard plug. Interspecific differences were found. Wood mice and striped field mice demonstrated consistently high success rates at all stages of the test, including the most difficult one (when the passage was blocked by a plug), indicating a well-developed ability to operate the object permanence rule. In contrast, the proportion of bank voles who solved the test decreased as the test complexity increased. Bank voles were also characterized by prolonged periods of immobility and lower levels of locomotion. The data suggest that interspecies variability in object permanence task solutions is associated not only with different levels of cognitive ability per se - but also with species-specific behavioral traits, which could be linked to the ecological specialization of these species.