Population Genetic Structure of a Microalgal Species under Expansion

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.

Phylogeography of the freshwater raphidophyte Gonyostomum semen confirms a recent expansion in northern Europe by a single haplotype

“…These results are in concordance with our previous population genetic study (Lebret et al. ), showing the presence of a single population in northern Europe. Low genetic diversity has been observed in the invasive range of several other species.…”

“…, Lebret et al. ), it could not be ruled out that G. semen colonized the lakes after the last ice age, and only increased in abundance recently due to more favorable conditions. In the latter case, we would have expected several different haplotypes of the cox1 marker in northern Europe as a result of multiple colonization events or diversification following the regression of the ice cap.…”

“…, Lebret et al. , Hagman et al. ) suggests that G. semen has invaded new lakes rather than only increased in number, and that this invasion is recent (past four or five decades).…”

“…Due to its increase in occurrence and expansion of its habitat range, G. semen is now viewed to be invasive in Norway, Sweden, and Finland (Lebret et al. , , Rengefors et al. , Hagman et al.…”

Asynchronous changes in abundance over large scales are explained by demographic variation rather than environmental stochasticity in an invasive flagellate

“…The expansion of G. semen in boreal lakes over the last decades (Lepistö, Antikainen & Kivinen ; Hagman et al . ) has attracted the interest of many researchers who have started to look into the drivers of distribution and bloom formation patterns of the flagellate (Rengefors, Weyhenmeyer & Bloch ; Lebret, Kritzberg & Rengefors ; Trigal et al . ; Karosiene et al .…”