Abstract
Adaptation to heterogeneous environments can occur via phenotypic plasticity, but how often this occurs is unknown. Reciprocal transplant studies provide a rich dataset to address this issue in plant populations because they allow for a determination of the prevalence of plastic versus canalized responses. From 31 reciprocal transplant studies, we quantified the frequency of five possible evolutionary patterns: (1) canalized response–no differentiation: no plasticity, the mean phenotypes of the populations are not different; (2) canalized response–population differentiation: no plasticity, the mean phenotypes of the populations are different; (3) perfect adaptive plasticity: plastic responses with similar reaction norms between populations; (4) adaptive plasticity: plastic responses with parallel, but not congruent reaction norms between populations; and (5) nonadaptive plasticity: plastic responses with differences in the slope of the reaction norms. The analysis included 362 records: 50.8% life-history traits, 43.6% morphological traits, and 5.5% physiological traits. Across all traits, 52% of the trait records were not plastic, and either showed no difference in means across sites (17%) or differed among sites (83%). Among the 48% of trait records that showed some sort of plasticity, 49.4% showed perfect adaptive plasticity, 19.5% adaptive plasticity, and 31% nonadaptive plasticity. These results suggest that canalized responses are more common than adaptive plasticity as an evolutionary response to environmental heterogeneity.
Highlights
Adaptation to environmental heterogeneity can occur in a variety of ways
For each of the studies selected, we recorded the mean of each trait, its variation, and sample size. We represent these reciprocal transplant experiments using the following notation: A in A (“AinA”) represents population A grown in its resident environment A, A in B (“AinB”) represents population A growing in the nonresident environment B, B in B (“BinB”) represents population B growing in its resident environment, and B in A (“BinA”) represents population B growing in the nonresident environment of population A (Fig. 1)
We considered a paired population record to consist of a population grown in both its resident and nonresident environment, for example, both AinA and AinB, and BinB and BinA are pairs
Summary
Adaptation to environmental heterogeneity can occur in a variety of ways. Populations can differentiate genetically so as to become locally adapted (Futuyma and Moreno 1988; Kawecki and Ebert 2004; Gould et al 2014) or individuals may be phenotypically plastic, expressing the optimal phenotype in both environments with no genetic differentiation (Bradshaw 1965; Schlichting 1986; Schlichting and Smith 2002). Plasticity has been suggested as an adaptive mechanism that allows plants to optimally respond to environmental heterogeneity (Alpert and Simms 2002; Callahan et al 2005). Nonadaptive plasticity can occur when a new environment induces a phenotype that is further away from the optimal phenotype (Ghalambor et al 2007)
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