An experimental test of state–behaviour feedbacks: gizzard mass and foraging behaviour in red knots
Mathot, K.J.; Dekinga, A.; Piersma, T. (2017). An experimental test of state–behaviour feedbacks: gizzard mass and foraging behaviour in red knots. Funct. Ecol. 31(5): 1111-1121. https://dx.doi.org/10.1111/1365-2435.12827
1. Animals frequently exhibit consistent among-individual differences in behavioural and physiologicaltraits that are inherently flexible. Why should individuals differ consistently in theirexpression of labile traits? Recently, positive feedbacks between state and behaviour have beenproposed as a possible explanation for the maintenance of consistent among-individual differencesin both state and behaviour. If state affects behaviour, and behaviour reciprocally affectsstate, then differences in either state or behaviour that arise among individuals even by chancecould be maintained over extended periods of time.2. We tested for positive feedbacks experimentally using wild-caught red knots (Calidris canutusislandica). In the wild, knots exhibit consistent among-individual differences in digestivephysiology (the mass of the muscular part of the stomach, the gizzard) and foraging behaviour(diet), two inherently labile traits.3. Experimentally manipulated diet quality had a large effect on gizzard mass. Experimentallymanipulated gizzard mass reciprocally influenced total food eaten during ad libitum trials.4. The effect of gizzard mass on diet choice, though in the predicted direction, was not statisticallysignificant. Individuals exhibited consistent differences in foraging behaviour of unknownorigin independent of current gizzard mass, as well as large residual unexplained variance inforaging behaviour. These two sources of variation in foraging behaviour overruled the gizzardmass-dependent foraging behaviour and hence eroded the treatment-related differences in gizzardmass.5. We conclude that positive feedbacks between diet choice and gizzard mass play at best alimited role in maintaining among-individual variation in gizzard mass in red knots. Furthermore,we suggest that many models of state–behaviour feedbacks likely overestimate theirpotential importance in maintaining long-term among-individual variation in labile traitsbecause most models of state–behaviour feedbacks fail to account for the effects of additionalfactors that may act to disrupt the feedback loops.6. The among-individual differences in diet choice observed during solitary foraging trialseroded the consistent among-individual differences in gizzard mass observed following periodsof staple diet treatments in which knots foraged in social groups. Social foraging interactionsmay play an important role determining the expression of foraging behaviours such as intakerate that in turn influence gizzard mass. Further studies are needed to experimentally test therole of social interactions as a mechanism generating consistent among-individual differencesin foraging behaviours and gizzard mass.
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