GENETICALLY BASED DIFFERENCES IN FORAGING BEHAVIOR AMONG SYMPATRIC MORPHS OF ARCTIC CHARR (PISCES, SALMONIDAE)

Four morphs of arctic charr, Salvelinus alpinus, coexist in the landlocked lake Thingvallavatn, Iceland. The morphs occupy different habitats and are segregated in diet year round. Feeding trials, involving laboratory-reared progeny of three morphs, indicated that several behavioural differences are genetically based, supporting the claim that the segregation among the morphs in Thingvallavatn is a consequence of adaptive trophic specializations. When Daphnia magna were fed, one at a time, progeny of small benthivorous charr noticed the prey earlier, and were more active, than progeny of planktivorous and piscivorous charr. Although prey rejection was more frequent among small benthivorous charr their feeding rate at high prey density equalled that of planktivorous chart. At lower prey densities small benthivorous charr, although showing reduced feeding rates, maintained higher feeding rates than the planktivorous fish. In the wild, planktivorous charr feed in the open pelagic, so this counterintuitive finding may indicate an innate 'predation-risk versus energy-gain trade-off. In the experiments the reluctance of the planktivorous fish to feed at low prey densities may reflect an adaptive decision mechanism geared to maximize energy returns. © 1993 The Association for the Study of Animal Behaviour. All rights reserved.