The role of familiarity in the development of social recognition by lambs
Résumé
A series of experiments investigated the role of association and familiarity in the development of social recognition among lambs. In each experiment, lambs were tested successively with 2 different social partners. When separated from their mothers, lambs that were paired with a partner with which they had been housed for 17 or 5 days emitted fewer distress bleats than they did during tests with an unfamiliar lamb. However, this effect was only evident when the test with the unfamiliar partner preceded the test with the familiar partner. When lambs were first tested with an unfamiliar partner treated with the same artificial odorant that had previously been associated with members of their own group, they bleated more than they did during a second test with a partner whose odor was novel. This effect was not observed when the familiar- and novel-odor partners were encountered in the reverse order. Bleating frequencies by lambs paired with their twin did not differ reliably from those of lambs paired with a familiar non-twin. Nonetheless, there was a significant correlation between the number of bleats by twins that were tested together. Overall, the results indicate that lambs become familiar with and recognize individuals (twins and non-twins) as a result of direct association. Lambs also discriminate between novel scents and artificial odorants associated with their familiar agemates, but such odors neither mask nor substitute effectively for lambs' individually recognizable phenotypes. Bleating frequency increases with the novelty of the social partner and of the test situation, and is therefore markedly affected by repeated testing.