Adaptive divergence generates distinct plastic responses in two closely related Senecio species

The evolution of plastic responses to external cues allows species to
maintain fitness in response to the environmental variation they regularly
experience. However, it remains unclear how plasticity evolves during
adaptation. To test whether distinct patterns of plasticity are associated
with adaptive divergence, we quantified plasticity for two closely related
but ecologically divergent Sicilian daisy species (Senecio, Asteraceae).
We sampled c.40 representative genotypes of each species from their native
range on Mt Etna and then reciprocally transplanted multiple clones of
each genotype into four field sites along an elevational gradient that
included the native elevational range of each species, and two
intermediate elevations. At each elevation we quantified survival and
measured leaf traits that included investment (specific leaf area),
morphology, chlorophyll fluorescence, pigment content and gene expression.
Traits and differentially expressed genes that changed with elevation in
one species often showed little change in the other species, or changed in
the opposite direction. As evidence of adaptive divergence, both species
performed better at their native site and better than the species from the
other habitat. Adaptive divergence is therefore associated with the
evolution of distinct plastic responses to environmental variation,
despite these two species sharing a recent common ancestor.