Illustration by Nina Sokolov We kicked off the first official Berkeley Ecology and Evolution of Infectious Disease Seminar with a talk by Professor Rodrigo Almeida from ESPM on his lab’s work on Xylella fastidiosa genetics in agricultural systems. Starting with an introduction to the system, Rodrigo outlined the biology of X. fastidiosa as a multi-host, multi-vector pathogen with high rates of recombination. X. fastidiosa is transmitted by leafhopper vectors that feed on the xylem sap of many plants and can cause severe epidemics and disease in agricultural systems. It has caused large epidemics both historically and recently, so its management is hugely important to people’s livelihoods and local and regional economies. Particularly interesting to my own interests of niche breadth evolution, Rodrigo let us know that this is a highly generalist pathogen, vector, and host complex. In natural ecosystems, he proposes that X. fastidiosa populations are likely composed of many genetically diverse strains that are transmitted by multiple vector species onto multiple host plant species, leading to high levels of strain mixing and recombination. In agricultural systems, there is often one strain of X. fastidiosa being transmitted by one vector species to single host agricultural monocultures. Interestingly, there is no specificity between what bacterial strains colonize which vectors, and the vectors are generalists too, but lots of specificity between bacterial strain and host plant when it comes to disease. Getting into his lab’s recent projects, Rodrigo outlined some of the work that post-doc Andreina Castillo Siri has done to look at how the high recombination rates of X. fastidiosa is associated with disease emergence into new host plants and environments. Rodrigo showed evidence that there is lots of gene flow between introduced and local native X. fastidiosa strains at the start of novel epidemics and shared some initial hypotheses for how recombination early in epidemics may help local adaptation, leading to recombined strains spreading early in epidemics, followed by recombination slowing down as the epidemic ages and there is more ecological isolation. The lab has started to explore this idea by comparing whether X. fastidiosa strains are donors or recipients of genes from both ancestral and recent recombination events in order to identify genes that have undergone recombination and may have been important for recent epidemics. The lab has also worked on historical outbreaks of X. fastidiosa, such as one in California grapevines since the late 1800s. This epidemic spread through California quickly, and, despite few geographic barriers to gene flow, has a highly geographically structured phylogeny with local diversification. These local strains of X. fastidiosa also appear to be recalcitrant to introduction of strains from other Californian regions, suggesting that they may be adapted to their local environments. Rodrigo presented work from Mathieu Vanhove exploring the landscape genomics of X. fastidiosa and how some SNPs correlated with temperature variation. Overall, Rodrigo’s presentation was an exciting start to the seminar series and the diversity of the work he presented highlighted the overlap between the all of our research groups. After a couple of questions, we wandered over to Raleigh’s for Happy Hour to turn our focus towards beers and catching up after the summer! Writing by Elisa Visher
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