Dispersal barriers and functional convergence in aquatic microorganisms

Last changed: 24 June 2024

For almost a century, microorganisms have been thought to have a worldwide distribution, leading to the famous hypothesis that "everything is everywhere, but the environment selects". But recent observations suggest that this may not be true at high phylogenetic resolutions.

Understanding the distribution of microorganisms is one of the challenges in modern ecoevolutionary research. Biogeographical patterns arise from an interplay of factors that were recently summarized in Vellend’s conceptual synthesis. Among them, dispersal limitation has long been thought to be insignificant for microorganisms given their high dispersal rates, which led to the adoption of Baas-Beking’s "everything is everywhere, but the environment selects" as one of the fundamental tenets of microbial biogeography. This view has started to be challenged by some authors, but reports are still contradictory, leading to a large controversy on whether microorganisms truly have global distributions or not.

One of the shortcomings in the field is that prior studies have generally been limited in taxonomic breadth and phylogenetic resolution. Only in the last years the advances in sequencing technologies and bioinformatics have allowed us to open the black box of microbial species diversity, revealing that our previous notions of bacterial "species" were really hiding hundreds of taxa. As such, what we previously thought to be a single globally distributed microorganism may actually be a collection of related but distinct geographical variants. This can have profound consequences depending on whether these variants are functionally equivalent or not.

In this project we will analyze more than 7000 publicly-available lake metagenomes and apply state-of-the art bioinformatics algorithms in order to:

  1. Study the biogeography of individual species, and compare it with the biogeography of individual genes, to assess the extent to which individual genes are bounds to certain clades.
  2. Assess whether there are signs of dispersal limitation in geographically distant populations from the same species, and whether dispersal limitation has the same effect in the core and accessory genomes.
  3. Assess whether dispersal limitation in lake microorganisms depends only on geographical distance or also is affected patch density

This project will for the first time produce a global intra-species level biogeography for freshwater microbial species.  By combining for the first time the concepts of dispersal limitation and intra-species functional redundancy at a global scale, this project will bring new perspectives to microbial biogeography and ecology, and help solve several outstanding controversies in the field.

Illustration of dispersal of microorganisms. Map.

Dispersal routes of lake microorganisms. Map by Fernando Puente Sanchez.