Food soiling and diet discrimination of mouse lines divergently selected for response to a nutritional toxicosis

Mouse lines were selected for eight generations for resistance (R) versus susceptibility (S) to growth depression from toxins in endophyte-infected tall fescue seed. To examine a possible correlated response to that selection, three experiments subsequently were conducted to examine food soiling behaviour of the mice. In Experiment 1, the average food soiling score was higher for R mice than S mice; but males had higher scores than females and soiling of the toxin-containing diet (T+) was greater than soiling of the non-toxin-containing diet (T−) only in the R line. When all mice received the T− diet during the first two weeks of Experiment 2, neither line, sex nor their interaction affected food soiling scores. During the second two weeks of Experiment 2, R mice had higher average food soiling scores than S mice on both the T− and the T+ diet; but within the R line, neither sex, diet nor their interaction significantly affected food soiling scores. In Experiment 3, when all mice had simultaneous access to both diets, bowls containing the T− diet were more heavily soiled than bowls containing the T+ diet, lines did not differ in soiling of the two diets, but males expressed greater diet soiling differences than females. In summary, after eight generations of divergent selection for growth depression from ingestion of fungal toxins, resistant and susceptible lines differed in food soiling behaviour, but not consistently across experiments. Differences could be attributable to genetic drift but might also represent correlated selection response in social, nutritional or emotional aspects of eliminative behaviour. Speculations about the biological and behavioural bases for observed differences may lead to testable hypotheses about how toxicosis resistance is inherited and expressed.