Chytrid epidemics may increase genetic diversity of a diatom spring-bloom

Abstract

Contrary to expectation, populations of clonal organisms are often genetically highly diverse. In phytoplankton, this diversity is maintained throughout periods of high population growth (that is, blooms), even though competitive exclusion among genotypes should hypothetically lead to the dominance of a few superior genotypes. Genotype-specific parasitism may be one mechanism that helps maintain such high-genotypic diversity of clonal organisms. Here, we present a comparison of population genetic similarity by estimating the beta-dispersion among genotypes of early and peak bloom populations of the diatom Asterionella formosa for three spring-blooms under high or low parasite pressure. The Asterionella population showed greater beta-dispersion at peak bloom than early bloom in the 2 years with high parasite pressure, whereas the within group dispersion did not change under low parasite pressure. Our findings support that high prevalence parasitism can promote genetic diversification of natural populations of clonal hosts.

Multi-year assessment of coastal planktonic fungi reveals environmental drivers of diversity and abundance

“…Freshwater diatoms have been shown to defend against chytrid infections via a range of mechanisms (Kagami et al, 2007). Analogous explanations for the loss of the Chytrid OTU14 in 2012 at Station L4 include diatom hosts developing anti-parasite defense mechanisms, such as the production of harmful chemicals (Pohnert et al, 2007), or changes within host populations towards more parasiteresistant genotypes (Gsell et al, 2013). Further studies are clearly needed to explore the relationships between diatoms and chytrids at Station L4, and the potential impacts of diatom-chytrid interaction on coastal ecosystem functioning.…”

Integrating chytrid fungal parasites into plankton ecology: research gaps and needs

“…Host geno-and/or chemotypes (i.e. differentiated by cellular oligopeptide fingerprints) can differ in resistance (Sønstebø and Rohrlack, 2011;Gsell et al, 2013b). Experimental evolution of chytrids shows fast adaptation in genetically homogeneous host cultures, but not in heterogeneous ones, indicating that host genetic diversity restricts parasite evolution (De Bruin et al, 2008).…”

“…parasitoids) and have the potential to inflict mass mortalities on their hosts, causing changes in phytoplankton size distributions, promotion of r-strategist hosts with fast turnover, delay or suppression of bloom formation and successional changes (Reynolds, 1973;Van Donk and Ringelberg, 1983;Van Donk, 1989;Rasconi et al, 2012;Gerphagnon et al, 2015;Gleason et al, 2015). Parasitism by chytrids mediates inter-and intraspecific competition and might promote diversity and polymorphisms in host populations (Gsell et al, 2013b). Chytrids are characterized by a free-living motile stage in the form of single-flagellated zoospores that are assumed to actively search for their hosts by chemotaxis (Canter and Jaworski, 1980;Muehlstein et al, 1988).…”

Exploring the impact of multidecadal environmental changes on the population genetic structure of a marine primary producer

“…Environmental heterogeneity (including biological interaction factors such as grazing and parasitism) also contributes to maintenance of genetic diversity (Bell, 2010;Gsell, Domis, Verhoeven, van Donk, & Ibelings, 2013). Indications that the effective population size of P. dalei are much smaller than total population size (Watts et al, 2013) raises questions of how high genetic diversity is maintained in P. dalei.…”