Succession or Co-blooming in Plankton – Correlating Genetic Distance and Fitness Difference

Jutta Hoffmann, Technical University of Berlin, Berlin, Germany, Kevin Vergin, Microbial DNA Analytics, Phoenix, OR, United States, Stephen J Giovannoni, Oregon State University, Department of Microbiology, Corvallis, OR, United States and Ferdi Hellweger, Technical University of Berlin, Water Quality Engineering, Berlin, Germany
Abstract:
Driven by advances in technology and need (e.g. identifying toxigenic and non-toxigenic genotypes) microbial observations are evolving to become increasingly resolved (micro-diversity). These high-resolution observations (e.g. genotypes) are challenging the traditional model of phytoplankton species succession because they frequently show great sequence diversity indicating potential co-blooming..

We hypothesize that co-blooming types (species, strains, genotypes, etc.), occupying similar ecological niches, are evolutionarily more related, and thus genetically closer than those showing succession. We test this hypothesis using a meta-analysis of plankton datasets. Specifically, we analyze marine and freshwater datasets and correlate fitness difference to genetic distance.

To quantify fitness differences, a selection coefficient (average population growth rate similarity)

is calculated for all pairs of types within each dataset. Our measure can be applied to absolute and relative abundance data.

Genetic distance is quantified using 16S rRNA average nucleotide distances (16S ANDs). For closely related types we base the distance on the 16S rRNA internally transcribed spacer (ITS) region and convert it to 16S AND. Conversion factors were obtained by creating libraries of species that allowed for calculation of 16S AND as well as 16S ITS AND. To allow for comparison of eukaryotes and prokaryotes, Rubisco subunit RbcL protein sequences or plastid 16S rRNA gene sequences were used and similarly converted.

Application of the method to several marine and freshwater datasets revealed a weak but consistently positive correlation between genetic distance and fitness differences. On a larger scale, these results could contribute to improved models that may address basic principles of diversity, ecology and evolution.

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