Cryptic invasion by a non-native genotype of the common reed, Phragmites australis, into North America

Abstract

Cryptic invasions are a largely unrecognized type of biological invasion that lead to underestimation of the total numbers and impacts of invaders because of the difficulty in detecting them. The distribution and abundance of Phragmites australis in North America has increased dramatically over the past 150 years. This research tests the hypothesis that a non-native strain of Phragmites is responsible for the observed spread. Two noncoding chloroplast DNA regions were sequenced for samples collected worldwide, throughout the range of Phragmites. Modern North American populations were compared with historical ones from herbarium collections. Results indicate that an introduction has occurred, and the introduced type has displaced native types as well as expanded to regions previously not known to have Phragmites. Native types apparently have disappeared from New England and, while still present, may be threatened in other parts of North America.

Figure 1

Parsimony network of Phragmites chloroplast haplotype diversity obtained from sampling 345 populations worldwide. Each link between haplotypes represents one mutational difference, following coding of indels as single characters. Unlabeled nodes indicate inferred steps not found in the sampled populations. Loops in the network are the result of homoplasies in the number of repeats in some indels. The ancestral haplotype, or root of the network, is indicated by a square. Geographic distribution of haplotypes is as follows: North America = haplotypes A-H, S, Z, AA, I, and M; South America = I and Y; Europe = L-O, and T; Asia/Australia = I, J, L, M, O, P, Q, U, W, and X; Africa = K, M, R, and V.

Figure 2

Distribution of Phragmites haplotypes in North America. Green triangles represent the 11 native haplotypes, blue squares represent haplotype I, and red circles represent the invasive haplotype M. (a and b) The distribution of haplotypes in the 62 herbarium samples collected before 1910. (c and d) The distribution of haplotypes in 195 samples collected after 1960.

Figure 3

Changes in Phragmites haplotype distribution patterns over 20-year time intervals in Connecticut, Massachusetts, and Rhode Island. Green triangles represent native haplotypes; red circles represent the invasive haplotype M.