Abstract
Biological invasions often cause major perturbations in the environment and are well studied among macroorganisms. Less is known about invasion by free-living microbes. Gonyostomum semen (Raphidophyceae) is a freshwater phytoplankton species that has increased in abundance in Northern Europe since the 1980's and has expanded its habitat range. In this study, we aimed to determine the genetic population structure of G. semen in Northern Europe and to what extent it reflects the species' recent expansion. We sampled lakes from 12 locations (11 lakes) in Norway, Sweden and Finland. Multiple strains from each location were genotyped using Amplified Fragment Length Polymorphism (AFLP). We found low differentiation between locations, and low gene diversity within each location. Moreover, there was an absence of genetic isolation with distance (Mantel test, p = 0.50). According to a Bayesian clustering method all the isolates belonged to the same genetic population. Together our data suggest the presence of one metapopulation and an overall low diversity, which is coherent with a recent expansion of G. semen.
Highlights
Invasive species can pose a significant threat to ecosystems with a wide range of effects on the newly colonized environment such as loss of biodiversity, disappearance of native species, shift in species dominance in the community, and alteration of ecosystem function [1]
While biological invasions in terrestrial and aquatic systems have been widely studied for a large range of macroorganisms, few studies focus on invasions of free-living aquatic microbes [2]
The survival rates of the isolates ranged from 22 to 51%, (Table 3). 614 Amplified Fragment Length Polymorphism (AFLP) loci were retained for the population genetic analyses
Summary
Invasive species can pose a significant threat to ecosystems with a wide range of effects on the newly colonized environment such as loss of biodiversity, disappearance of native species, shift in species dominance in the community, and alteration of ecosystem function [1]. While biological invasions in terrestrial and aquatic systems have been widely studied for a large range of macroorganisms, few studies focus on invasions of free-living aquatic microbes [2]. Microbes were for a long time considered to be cosmopolitan due to their high dispersal capacity and large population sizes [3], and not viewed as potential invaders. Studies concerning invasive phytoplankton are scarce, and only a handful of microalgal species are currently described as invasive. These include the marine dinoflagellate Alexandrium tamarense [5], the freshwater cyanobacteria Aphanizomenon ovalisporum and Cylindrospermopsis raciborskii [6,7], and the freshwater raphidophyte Gonyostomum semen [8,9]
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