Abstract
Population genetic studies provide insights into intraspecific diversity and dispersal patterns of microorganisms such as protists, which help understanding invasions, harmful algal bloom development and occurrence of seafood poisoning. Genetic differentiation across geography has been reported in many microbial species indicating significant dispersal barriers among different habitats. Temporal differentiation has been less studied and its frequency, drivers and magnitude are poorly understood due to a lack of integral studies. The toxic dinoflagellate species Gambierdiscus caribaeus was sampled during two years in the Florida Keys, and repeatedly from 2006 to 2016 at St. Thomas, US Virgin Islands (USVI), including a three-year period with monthly sampling, to compare spatial and temporal genetic differentiation. Samples from the USVI site showed high temporal variability in local population structure, which correlated with changes in salinity and benthic habitat cover. In some cases, temporal variability exceeded spatial differentiation, despite apparent lack of connectivity and dispersal across the Greater Caribbean Region based on the spatial genetic data. Thus, local processes such as selection might have a stronger influence on population structure in microorganisms than geographic distance. The observed high temporal genetic diversity challenges the prediction of harmful algal blooms and toxin concentrations, but illustrates also the evolutionary potential of microalgae to respond to environmental change.
Highlights
Population genetic studies of microorganisms provide valuable insights into intraspecific variability and evolutionary processes due to their short generation times and large population sizes (Elena and Lenski, 2003)
To assess temporal and spatial genetic differentiation, we focused on Gambierdiscus caribaeus, a common species at our study sites in the Greater Caribbean Region (GCR), and investigated its population structure using isolates from the Florida Keys and St
Samples collected at the Florida Keys and at US Virgin Islands (USVI) before the high-resolution sampling period represent yearly collections and are denoted with sampling region (USVI or FlK) and year There were 293 unique seven-locus genotypes in the entire data set resulting in an overall genotype diversity of 0.72 (G/N)
Summary
Population genetic studies of microorganisms provide valuable insights into intraspecific variability and evolutionary processes due to their short generation times and large population sizes (Elena and Lenski, 2003). Successful genotypes can quickly increase in number due to asexual reproduction and impact the population structure on relatively short time scales, demonstrating microevolution in “fast motion” (e.g., Richlen et al, 2012) Microorganisms such as microalgae can be useful study organisms to investigate evolutionary response to different environmental conditions, e.g., after dispersal or due to climate change, and its impact on population structure. The majority of the investigated, mainly planktonic microalgal species display genetically distinct populations and exhibit significant divergence over different spatial scales despite the absence of obvious dispersal barriers in most aquatic habitats (Foissner, 2006; Vanormelingen et al, 2008; Lowe et al, 2010; Rengefors et al, 2012; Godhe et al, 2016) This divergence can result from limited gene flow between populations due to isolation by geographic distance (Casteleyn et al, 2010; Orsini et al, 2013). Environmental variables have been shown to significantly impact genetic differentiation in microalgae (Boenigk et al, 2007; Souffreau et al, 2013; Rengefors et al, 2014) due to natural selection and local adaptation of populations (Hendry, 2004)
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