Contribution of phenotypic plasticity and heredity to the trophic polymorphism of lacustrine brook charr (Salvelinus fontinalis M.)

The results show that morphological differences between littoral and pelagic brook charr are heritable and related to both genetic and environmental factors.

Abstract

The objectives of this study were to determine: (1) if morphological characters of littoral and pelagic brook charr are inherited by their progeny when both forms are raised in the same conditions; (2) if sexual dimorphism would account for part of the variation in littoral and pelagic brook charr morphology; (3) the relative contribution of genetic and environmental factors to trophic polymorphism of brook charr; and (4) if a fish that had already performed one plastic response can reverse this response in a functional direction when shifted to an alternative habitat (e.g. littoral to pelagic). We conducted a reciprocal transplant experiment over 16 months after hatching in which fish of both ecotypes were fed in artificial pelagic (prey captured in the water column) and littoral (prey captured on the bottom) habitats. The results show that morphological differences between littoral and pelagic brook charr are heritable and related to both genetic and environmental factors. The percent variation of fish morphology explained by the effects of genetic and environmental factors was 17 % and 15 % respectively when the effect of sex was controlled, and 13 % and 26 % respectively when the effect of sex was not accounted for, indicating that sexual dimorphism accounts for an important part of the overall variation in brook charr morphology. The shift of some individuals from their initial to the opposite habitat from months 12–16 highlighted the role of the genetic and environmental factors as well as the magnitude of morphological plasticity: some characters remained unchanged during this 4-month shift, while some others exhibited a complete reversal, in line with the predictions of functional morphology. This result indicates that some characters are under pure environmental control and are not fixed after a fish has adopted a given strategy.