The relative importance of mother and toxicosis in the selection of foods by lambs.

A lamb's mother and postingestive feedback both influence learning about foods, but their relative importance is unknown. We conducted a study to compare the ingestion of elm (1) by lambs whose mothers avoided elm because ingestion of elm by mother was previously paired with the toxin lithium chloride (LiCl) (M), (2) by lambs who received a mild dose of LiCl after they ingested elm, and whose mothers also avoided elm (M + L), and (3) by lambs who received LiCl after they ingested elm, but whose mothers ate elm avidly (M vs. L); in treatment (4) neither mothers nor lambs were given LiCl (C). In all four treatments, mothers and lambs ate poplar. Each lamb was exposed with its mother for 5 min/day to poplar on days 1,2, 5, 7, 9, and 11 and to elm on days 3, 4, 6, 8, 10, and 12. Following exposures to elm on days 8, 10, and 12, lambs in treatments M + L and M vs. L were given a low dose of LiCl (100 mg/kg body weight orally in a capsule) when they ingested elm to produce an aversion to elm. During the first test after weaning, lambs could choose between elm and poplar. Lambs in C took more bites of elm than did lambs in M, M + L, and M vs. L (13, 2, 2, < 1;P >F=0.003), and they also took a higher percentage of bites from elm (42, 11, 6, 1;P >F < 0.001). The number of bites of poplar did not differ among treatments (M=31, M + L=26, M vs. L=42, C=27;P >F =0.458). During the second test, when lambs were offered only elm, lambs in C took significantly more bites of elm than those in the other treatments, and lambs in M took more bites of elm than lambs in M + L, but not M vs. L (C=38, M=16, M + L=3, M vs. L=6;P >F < 0.001). During the third test, when lambs again could choose between elm and poplar, lambs in C again took more bites of elm (C=14, M=3, M + L=< 1, M vs. L=< 1;P >F=0.034), and they also took a higher percentage of bites from elm (C=26, M=5, M + L=2, M vs. L=2;P >F < 0.001), than did lambs in the other three treatments. The number of bites of poplar did not differ among treatments (M=47, M + L=43, M vs. L=62, C =41;P >F=0.223). We conclude that the response by lambs to the toxin LiCl was more important than was the mother as a social model because lambs that received LiCl avoided elm whether or not the mother ate it.