Phylogeography reveals a potential cryptic invasion in the Southern Hemisphere of Ceratophyllum demersum, New Zealand\u2019s worst invasive macrophyte

Benita Hyldgaard,Hans Brix,Carla Lambertini

doi:10.1038/s41598-017-16712-8

Abstract

Ceratophyllum demersum (common hornwort) is presently considered the worst invasive submerged aquatic macrophyte in New Zealand. We explored the global phylogeographic pattern of the species, based on chloroplast and nuclear DNA, in order to identify the origin of the invasive populations in New Zealand and to clarify if there were multiple introductions. The phylogeographic study identified geographically differentiated gene pools in North America, tropical Asia, Australia, and South Africa, likely native to these regions, and a recent dispersal event of a Eurasian-related haplotype to North America, New Zealand, Australia, and South Africa. At least two different invasive genotypes of this Eurasian-related haplotype have been found in New Zealand. One genotype is closely related to genotypes in Australia and South Africa, while we could not trace the closest relatives of the other genotype within our C. demersum sample set. Contrasting spectra of genetic distances in New Zealand and in a region within the native range (Denmark), suggest that the invasive population was founded by vegetative reproduction, seen as low genetic distances among genotypes. We also discovered the introduction of the same Eurasian-related haplotype in Australia and South Africa and that a cryptic invasion may be occurring in these continents.

Highlights

Global trade and transport has dramatically increased the number of alien plant species and populations introduced to novel areas either intentionally or accidentally by human activity[1,2]
Samples of C. demersum were collected from all over the world to investigate the phylogeography of the species and trace the origin of the invasive populations in New Zealand
Ceratophyllum demersum was separated from C. submersum in both trees with 100% support

Summary

Introduction

Global trade and transport has dramatically increased the number of alien plant species and populations introduced to novel areas either intentionally or accidentally by human activity[1,2]. In some instances, introduced genotypes may have conspecific native populations in the invaded range and be morphologically similar to the native genotypes but sufficiently different in ecology or physiology to become invasive and outcompete the conspecific native populations as well as other species This type of invasion is called cryptic, as the new invaders are difficult to distinguish from native populations due to their morphological resemblance[10]. We assessed the role of genetic differentiation in the invasion in New Zealand, i.e. if the invasion is driven by a population with high genetic diversity, and has potential for rapid evolution, or by one or few genotypes with high phenotypic plasticity[17] We used both chloroplast DNA sequences (cpDNA sequences) to trace long-distance dispersal events, and nuclear amplified fragment length polymorphisms (AFLPs) to resolve intra-haplotypic relationships (i.e. between individuals sharing chloroplast DNA), within distribution ranges

Methods

Results

Conclusion