Data from: Small-scale genetic differentiation in mean flowering time, but not in plasticity, along a geothermal heating gradient

Genetic differentiation in traits is assumed to frequently occur in
response to divergent natural selection. For example, developmental traits
might respond to differences in climate. However, little is known about
when and at which spatial scales environmental differences lead to genetic
differentiation, and to what extent there is genetic differentiation also
in trait plasticity. Using a crossing design and a greenhouse heating
experiment, we investigated genetic differentiation in the thermal
sensitivity of flowering time in a perennial herb along small-scale
gradients in geothermal soil heating in Iceland. We found additive genetic
variation in both flowering time and thermal plasticity of flowering time.
Genetic differentiation in the median flowering date of individuals showed
a counter-gradient pattern; flowering being earlier at higher greenhouse
temperatures, while at a given temperature individuals originating from
warmer soils flowered later than individuals from colder soils. We found
no corresponding pattern for plasticity, suggesting that genetic
differentiation in phenology in response to soil heating has occurred
through changes in trait means rather than in plasticity. Findings such as
these, identifying genetic trait differentiation along an environmental
gradient are key to understanding how environmental variation can drive
the process of local adaptation, and to predict responses to future
environmental changes.