Adaptive Differentiation in the General-Purpose Genotype Invasive Plant Erythranthe guttata

Highly plastic general-purpose genotypes are a frequent occurrence among invasive plants. Yet, it remains uncertain to what extent genetic adaptation can co-occur with such elevated levels of plasticity. Understanding the interplay between these two evolutionary strategies is essential to better predict invasive success and future climate change responses.

We investigated the potential for local adaptation along an altitudinal gradient in introduced New Zealand populations of the highly plastic invasive herb, Erythranthe guttata . We asked a) whether there were phenotypic differences between upland and lowland E. guttata populations along our gradient; b) whether any differences were consistent with known adaptive patterns; and c) whether any adaptive patterns exist alongside high plasticity to elevation.

Samples from 38 E. guttata populations from upland and lowland Canterbury were grown from cuttings in a lowland and an upland common garden, where we measured a broad range of growth and reproductive traits.

We found significant adaptive differentiation between upland and lowland populations over almost all measured traits. Upland populations had earlier and more intense flowering compared with lowland populations. Lowland plants were taller and had larger leaves with higher photosynthetic rates than upland plants. These differences occurred alongside high levels of unspecialised plasticity to the growing environment.

Synthesis: We found that over a period of less than 150 years the environment along an altitude gradient of 120km has selected for distinct lowland and upland phenotypes of E. guttata . These changes reflect common selective pressure associated with altitude gradients, increasing reproductive success at higher altitudes and increased competitive ability at lower altitudes. This rapid local adaptation occurred alongside high plasticity within the growing environment, showing that highly plastic invasive species still retain the capacity to genetically adapt to novel environments.