Genome‐wide single nucleotide polymorphism markers reveal population structure and dispersal direction of an expanding nuisance algal bloom species

Abstract

Species invasion and range expansion are currently under scrutiny due to increasing anthropogenic impact on the natural environment. This is also true for harmful algal blooms, which have been reported to have increased in frequency. However, this research is challenging due to the ephemeral nature, small size and mostly low concentrations of microalgae in the environment. One such species is the nuisance microalga Gonyostomum semen (Raphidophyceae), which has increased in occurrence in northern Europe in recent decades. The question of whether the species has expanded its habitat range or if it was already present in the lakes but was too rare to be detected remains unanswered. The aim of the present study was to determine the genetic structure and dispersal pathways of G. semen using RAD (restriction‐site‐associated DNA) tag sequencing. For G. semen, which has a huge genome (32 Gbp), we faced particular challenges, but were nevertheless able to recover over 1000 single nucleotide polymorphisms at high coverage. Our data revealed a distinct population genetic structure, demonstrating a divide of western and eastern populations that probably represent different lineages. Despite significant genetic differentiation among lakes, we found only limited isolation‐by‐distance. While we had expected a pattern of recent expansion northwards, the data demonstrated gene flow from the northeast/east towards the southwest/west. This genetic signature suggests that the observed gene flow may be due to dispersal by autumn migratory birds, which act as dispersal vectors of resistant resting propagules that form at the end of the G. semen blooms.

The Role of Genetic Factors in the Differential Invasion Success of Two Spartina Species in China

“…Most previous studies also revealed that outcrossing of plants from the locations of origin (North Carolina, Georgia, and Florida in the US) of S. alterniflora generated a genetic admixture, and genetic variation remained high compared to those in the native populations ( Bernik et al, 2016 ; Qiao et al, 2019 ; Xia et al, 2020 ). Moreover, only the TG and CX populations had higher expected heterozygosity ( He , 0.145 and 0.115) than observed heterozygosity ( Ho , 0.121 and 0.110), which may have been a reflection of earlier population bottlenecks ( Rengefors et al, 2021 ), whereas, other populations did not show evidence of bottlenecks. Therefore, neither of the two Spartina species in China showed the genetic paradox of invasion.…”

Best practices in the flow cytometry of microalgae

“…Alternatively, bead-beating of cells in a mixer mill can be employed to isolate nuclei. This method was particularly successful in the raphydophyte Gonyostomum semen [30]. In many cases, however, enzymatic treatment to disrupt cell walls needs to be implemented before protoplast content extraction [4,11,31].…”

“…In studies on microalgae, commonly-used buffers are LB01 (with streptophytes, Chlorophyta, Ochrophyta, raphidophytes; [4,11,30]), a MOPS-based buffer (3-(N-morpholino) propanesulfonic acid (used with dinoflagellates; [21,24]), or Otto buffers (with chrysophytes; [16,29]). Triton X-100 (to a final concentration of 0.05%-1%) may be added to improve the sample staining, though its effect varies across different groups of algae [2,7,14,19,34].…”

Seasonal genotype dynamics of a marine dinoflagellate: Pelagic populations are homogeneous and as diverse as benthic seed banks

“…Genomic DNA was digested with high-fidelity SbfI (New England Biolabs), applying a RAD library preparation protocol modified from Amores et al (2011) and Etter et al (2011). Modifications (according to Rengefors et al, 2021) included an increased amount of ligase (2000 U µl -1 T4 ligase) and decreased volume of NEB2 buffer (1 µl).…”