Premium
Rats Work for Food They then Reject: Support for the Information‐primacy Approach to Learned Industriousness
Author(s) -
Inglis I. R.,
Shepherd D. S.
Publication year - 1994
Publication title -
ethology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.739
H-Index - 74
eISSN - 1439-0310
pISSN - 0179-1613
DOI - 10.1111/j.1439-0310.1994.tb01066.x
Subject(s) - pellets , lever , pellet , zoology , toxicology , test (biology) , food consumption , psychology , biology , ecology , engineering , economics , agricultural economics , paleontology , mechanical engineering
There is good evidence that in many situations, animals prefer to work for food even when identical food is freely available. This phenomenon is called ‘learned industriousness’ or ‘contrafreeloading’ and has been found in several species. This study shows that wild rats will also work hard for contaminated food that they associate with sickness and subsequently reject, even when wholesome food is continuously available at no extra cost. Seven wild rats ( Rattus novegicus ) lived for 4 wk in cages containing two operant levers and associated pellet dispensers. The rats earned all their food by lever pressing for 45‐mg food pellets on a variable‐interval 10 s (VI10s) schedule in each dispenser. After 1 wk, pellets containing a sub‐lethal dose of an acute rodenticide were available for 12 h (the test period) from the preferred dispenser, before being replaced by normal food pellets. This procedure was repeated 1 wk and 4 wk later. The number of lever presses, pellets delivered, and pellets consumed at each dispenser were recorded for 12 h prior to the test period, during the 12‐h test period, and 12 h after the test period. The rats quickly learned to shift their feeding preference during the test period away from the dispenser that provided the rodenticide pellets. However, during the second half of the test period, lever pressing at this dispenser increased, even though the pellets thereby obtained were still rejected. This divergence between the lever pressing rate and the pellet consumption rate increased over the three trials. This ‘learned‐industriousness’ behaviour is not easily explained by the self‐reinforcing hypothesis, by the obligate species‐specific response hypothesis, or as some artefact of the operant situation. It is suggested that the lever pressing towards the end of the trial, for pellets that were rejected, enabled the animals to gather information about a rare, but very important, event, namely, the presence of dangerous food at a previously preferred and normally safe feeding site. The data lend support to the information‐primacy theory of learned industriousness.