SG: Spatial and environmental barriers to gene flow driving cyanobacterial biogeography in a river network.

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Humans rely on bacteria for nutrient recycling and many other essential functions. Scientists continue to discover increasing bacterial diversity as molecular methods improve. However, scientists do not understand how this genetic diversity relates to the evolution of new and ecologically important species. Better understanding of the processes that create bacterial diversity is needed, particularly in light of their useful functions in ecosystems. This research will study a group of bacteria, the cyanobacteria, that use light to sequester carbon and produce oxygen. New cyanobacterial species may form when barriers, such as distance or environmental conditions, isolate them and reduce the exchange of genes across populations. That exchange is called "gene flow". No one knows if it is distance, or the differences in environment, that prevent gene flow in these important organisms. This project will collect mats of cyanobacteria throughout the Eel River of Northwestern California, and the researchers will investigate the genetic similarity of those mats across different locations. Cyanobacteria will be sampled from distant locations with similar environments and adjacent locations with different environments. The data will be used to determine what is most important in creating cyanobacterial diversity. A local media organization will collaborate on the project. They will help a group of high school students to create a short science documentary film. Students will film the research done in the field and in the lab to gain knowledge about science communication. Their film and the project findings will be used by local schools.  This research will investigate genomic patterns and ecological processes that suggest how spatial and environmental barriers to gene flow differentiate cyanobacterial populations, generating nascent genetic diversity. These barriers are predicted to produce different patterns of nucleotide differentiation at neutral and adaptive loci. Therefore, more understanding of the processes driving biogeographical patterns of microbes can be achieved with analyses of closely related co-existing wild bacterial populations collected over variety of spatial scales. Benthic cyanobacterial mats (Phormidium spp.) and environmental variables will be sampled in the river network in a nested design spanning pairwise distances of centimeters to hundreds of kilometers across diverse habitats, from warm sunny downstream habitats to cool shaded tributaries. Using whole genome metagenomic analyses, patterns of nucleotide variation at loci throughout the genome will be compared and will be used to understand 1) the strength of sub-species population diversity in a widespread cyanobacterial genus, 2) the spatial scales of cyanobacterial population diversity, and 3) the contributions of spatial and environmental barriers to gene flow in driving the observed biogeographical patterns.