Gut decisions can involve social choices

Posted on January 5, 2013

To a large extent, traditional foraging theory has been concerned with explaining how behavioural strategies help animals maximise their energy intake.  However, there’s a growing recognition that foragers can choose foods on the basis of nutrient quality as well as quantity.  While energy can be derived from protein, fat or carbohydrate, protein is particularly crucial due to its ability to act as an essential nitrogen source for body maintenance, growth, and reproduction.   Using the mosquitofish (Gambusia holbrooki) as a test species, Australian researchers assessed the sensitivity of fish to direct foraging cues (the odours of foods with high or low protein content) and indirect cues (the odours of other mosquitofish that had been recently fed on high or low protein diets for 72 hours).  Test fish were placed in a flow chamber where they could choose between water streams carrying odours from different header tanks.   When presented with odour cues from agar blocks containing foods with a high (27%) or low (3%) protein content, fish showed a significant preference for the high-protein odour.  In a separate experiment where the incoming water stream came from tanks holding sticklebacks that had been maintained on one or other of the two diets, the test fish preferred water from the “high-protein” tank, and interestingly, the preference was stronger than in the first experiment, where food cues were direct rather than indirect.  In a third experiment, male test fish attempted to mate more often with female mosquitofish that had been given the high-protein diet than with females given the low-protein food.  This study is the first to show that fish can show a preference for other members of the same species based on diet quality, as opposed to just a shared recent experience of the same habitat or diet.  Presumably, this ability confers advantages by allowing fish to benefit by associating with successful foragers and to choose mates that are more likely to be in good reproductive condition.

Reference:  Ward, A.J.W., Herbert-Read, J.E. & Simpson, S.J.  2011.  Diets and decisions: the potential use of food protein cues in dietary, sexual and social decisions by mosquitofish.  Animal Behaviour 82, 783-790.