Strong differentiation between ancestral populations from low and high elevation: Implications for invasion biology.

PREMISE The differentiation of native populations at regional scales may limit evolutionary inferences derived from comparisons between native and non-native populations in common gardens, but little is known about how native populations of invasive species vary along environmental gradients at a regional scale.

METHODS We used a common garden to explore differentiation in several traits between ancestral populations of Centaurea solstitialis growing at low and high elevation in southwestern Anatolia, a region considered to be one of the sources that contributed to the global expansion of this species.

RESULTS Population differentiation was strong for all studied traits. Populations from low elevation produced smaller seeds, emerged and grew faster, flowered earlier, produced smaller and more numerous capitula per plant, and had larger individuals than those from high elevation. However, seed production per individual in low-elevation populations was similar to that in high-elevation populations because the capitula in high-elevation populations produced more seeds. Most notably, the seed type bearing a pappus was more abundant in higher-elevation populations than lower, but the abundance of non-pappus seeds exhibited no differences between those populations (capitulum level) or decreased with elevation (individual level).

CONCLUSIONS Our findings highlight the need to consider intraspecific variation at regional scales within native ranges, when attempting to infer evolutionary consequences based on comparisons between native and non-native populations of invasive species. Furthermore, a strong inference of evolutionary change in non-native populations may require knowledge of interpopulation variation even within regions identified as donors of those populations.