Abstract
Genetic diversity in marine microbial eukaryotic populations (protists) drives their ecological success by enabling diverse phenotypes to respond rapidly to changing environmental conditions. Despite enormous population sizes and lack of barriers to gene flow, genetic differentiation that is associated with geographic distance, currents, and environmental gradients has been reported from planktonic protists. However, for benthic protists, which have reduced dispersal opportunities, phylogeography and its phenotypic significance are little known. In recent years, the East Australian Current (EAC) has intensified its southward flow, associated with the tropicalization of temperate waters. Benthic harmful algal species have been increasingly found in south‐eastern Australia. Yet little is known about the potential of these species to adapt or extend their range in relation to changing conditions. Here, we examine genetic diversity and functional niche divergence in a toxic benthic dinoflagellate, Ostreopsis cf. siamensis, along a 1,500 km north–south gradient in southeastern Australia. Sixty‐eight strains were established from eight sampling sites. The study revealed long‐standing genetic diversity among strains established from the northern‐most sites, along with large phenotypic variation in observed physiological traits such as growth rates, cell volume, production of palytoxin‐like compounds, and photophysiological parameters. Strains from the southern populations were more uniform in both genetic and functional traits, and have possibly colonized their habitats more recently. Our study reports significant genetic and functional trait variability in a benthic harmful algal species, indicative of high adaptability, and a possible climate‐driven range extension. The observed high trait variation may facilitate development of harmful algal blooms under dynamic coastal environmental conditions.
Highlights
Microbial eukaryotes are an essential component of marine ecosystems, driving productivity and biogeochemical cycles (Falkowski et al, 2004)
We report a multitude of coexisting phenotypic characteristics in a subset of O. cf. siamensis strains isolated from eight geographic populations along the coastal regions of the East Australian Current (EAC), suggestive of a broad capacity to acclimate to a wide range of environmental conditions in highly variable habitats
Variability in the investigated phenotypic traits is independent of the clustering of strains into distinct genotypic subclades, but more significant among strains from the northern geographic populations, similar to the trend observed with the genetic data, suggestive of a more diverse and adaptive population in the northern subtropical regions of the EAC with a larger number of “eco-” and “geno-“ types”
Summary
Microbial eukaryotes (protists) are an essential component of marine ecosystems, driving productivity and biogeochemical cycles (Falkowski et al, 2004). Recent studies have shown phylogeographic structure to be reflective of historical (dispersal limitation), ecological (divergence resulting from local selection), and/or local adaptive conditions (trait-based niches) (Casteleyn et al, 2010; Ellison et al, 2011; Litchman & Klausmeier, 2008; Litchman, Klausmeier, Schofield, & Falkowski, 2007; Nagai et al, 2007; Tahvanainen et al, 2012) This suggests that marine microbial eukaryotes should be considered as consortia of genetically structured “meta-populations” with low dispersal rates (isolation by physical and/or ecological barriers), rather than single panmictic populations (Casabianca et al, 2011; Sjöqvist, Godhe, Jonsson, Sundqvist, & Kremp, 2015). Results from this study provide novel insights into the phylogeographic structure and large phenotypic trait variation within benthic HAB populations along the EAC, which potentially facilitate bloom development under dynamic environmental conditions and promote the success of HABs during global environmental change
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