Signs of local adaptation and phenotypic plastic response to elevation shifted between environmental backgrounds in Snapdragon plants

Multiple environmental drivers can shape the plastic and microevolutionary adaptive responses of plants. Yet experimental studies on local adaptation and phenotypic plasticity rarely investigate how different backgrounds might interact and modify the signature patterns of these mechanisms. Here, we evaluated local adaptation and plasticity in response to elevation in two Snapdragon plant subspecies (Antirrhinum majus striatum and A. m. pseudomajus) by using common garden experiments at different elevations. We tested whether the phenotypic signatures of plasticity and local adaptation recorded in an open habitat were similar between subspecies and maintained when the experiment was replicated onsite under the shade of understory vegetation. Our results showed that population genetic divergence in germination-related traits was suggestive of a pattern of local adaptation to elevation under regular sunlight in A. m. striatum, but not in A. m. pseudomajus. They also revealed potentially neutral or adaptive plastic responses to elevation for these traits. The magnitude of plastic responses was stronger than trait genetic divergence. Under understory shade, phenotypic patterns were different and suggested maladaptive or neutral responses to elevation. Our findings imply that the genetic and plastic adaptive signatures of elevation cannot be inferred without taking into account the variability of the environmental background. They also imply that selection mechanisms linked to germination vary across heterogeneous environments in Snapdragon plants. Forecasting the ability of plants to adapt to environmental changes based on common garden and reciprocal transplant experiments must account for the multivariate nature of the environment.