Morphometrical characteristics of cryptic invasive and indigenous gene pools of field maple Acer campestre L. in southern Sweden

Abstract

The northernmost population of Acer campestre L. has its distribution in southern Sweden and consists of just 36 individuals. This particular remnant is considered critically endangered (CE) although the species spreads rapidly as potentially invasive gene pools escaped from gardens and urban plantations. The issue to distinguish between indigenous and introduced gene pools is urgent, since individuals or stands worthy of preservation risk being cut down. This article explores the possibility to use geometric morphometrics by landmarks to characterize shapes of leaves and samaras and to distinguish different gene pools. Bayesian clustering based on microsatellite data clearly distinguished between putatively native and introduced gene pools in southern Sweden. A discriminant analysis of Procrustes coordinates of leaf shapes gave 77% correct classification revealing a strongly concave leaf base for the native gene pool and a convex leaf base for the introduced ones. Corresponding analyses of the samara data resulted in 82% correct classification. In general, the discrimination rate for samara shape was higher than for leaf shape, suggesting a stronger influence of differences between individual and populations. However, PCA clearly showed that the variation in the native gene pool represents a subset of the variation seen in the introduced gene pool, both for leaf and samara shape. An easy to apply method to distinguish between native and introduced gene pools are thus not to be expected from shape data.