The evolutionary and ecological significance of heterophylly in aquatic plants : a case study in the genus Proserpinaca (Haloragaceae).

Natural habitats are temporally and spatially variable, and organisms express a multitude of strategies in coping with this environmental heterogeneity (Levins 1968). At the level of the individual, genotypes faced with such conditions may either produce the same phenotype (homeostasis) or express different phenotypes in response to specific environmental cues (phenotypic plasticity). In the case of the former, one may speak of populations consisting of different, coexisting yet tightly canalized phenotypes, each of which is adapted to a subset of the conditions experienced by the population (genetic polymorphism, Waddington 1942; Lerner 1954). With respect to the latter, populations may be comprised of individuals capable of functionally appropriate responses mediated through the processes of organismal development and physiology (Schlichting and Pigliucci 1998). Both of these constitute fundamental modes of adaptation to life in heterogeneous environments.