Phenotypic plasticity and genetic differentiation
While no host-associated genetic divergence has been observed within C. galea, adaptive genetic polymorphisms may still play a role, and the relative importance of both a genetic basis and phenotypic plasticity to variation in morphology remains unknown (Johnston et al., 2012). Both mechanisms are not mutually exclusive, as both genetic differentiation and phenotypic plasticity are thought to play a role in the adaptation of the snail Littorina saxatilis (Olivi, 1792) to the local habitat (Janson, 1983; Johannesson and Johannesson, 1996; Hollander et al., 2006). Reciprocal transplant experiments of C. galea among different host species showed that current host species was a more important determinant for growth than the native host species, suggesting that phenotypic plasticity plays at least some role in the morphological variation of C. galea (Baums et al., 2003b). Johnston et al. (2012) also attributed difference in growth rates at least partly to phenotypic plasticity. These results suggest that within C. galea, habitat-related phenotypic plasticity is more important than evolutionary divergence, although the intraspecific genetic variation observed within C. caribaea does not preclude a role for phenotypic plasticity within this species.