RATS WORK FOR FOOD THEY THEN REJECT - SUPPORT FOR THE INFORMATION-PRIMACY APPROACH TO LEARNED INDUSTRIOUSNESS

There is good evidence that in many situations, animals prefer to work for food even when identical food is freely available. This phenomeno n is called 'learned industriousness' or 'contra-freeloading' and has been found in several species. This study shows that wild rats will al so work hard for contaminated food that they associate with sickness a nd subsequently reject, even when wholesome food is continuously avail able at no extra cost. Seven wild rats (Rattus novegicus) lived for 4 wk in cages containing two operant levers and associated pellet dispen sers. The rats earned all their food by lever pressing for 45-mg food pellets on a variable-interval 10s (VI10s) schedule in each dispenser. After 1 wk, pellets containing a sub-lethal dose of an acute rodentic ide were available for 12 h (the test period) from the preferred dispe nser, before being replaced by normal food pellets. This procedure was repeated 1 wk and 4 wk later. The number of lever presses, pellets de livered, 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 afte r the test period. The rats quickly learned to shift their feeding pre ference during the test period away from the dispenser that provided t he rodenticide pellets. However, during the second half of the rest pe riod, lever pressing at this dispenser increased, even though the pell ets 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 nor, easily explained by the self-reinforcing hypothesis, by the obligate species -specific response hypothesis, or as some artefact of the operant situ ation. 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 prese nce of dangerous food at a previously preferred and normally safe feed ing site. The data lend support to the information-primacy theory of l earned industriousness.