Population genomics reveals patterns of divergence and gene flow between populations of Fusarium subglutinans and Fusarium temperatum in Argentina

FUMERO MARÍA VERÓNICA; YUE, WEI; CHIOTTA MARIA LAURA; CHULZE, SOFÍA N.; LESLIE, JOHN F.; TOOMAJIAN, CHRISTOPHER

Conferencia; 30th Fungal Genetics Conference.; 2019

Recent studies have made it clear that species boundaries between fungi can be semipermeable, and call into question the utility of a bifurcating species tree as a model. More data are needed on how this semipermeability affects the speciation process and what this implies for adaptive evolution, especially in pathogenic species. Fusarium subglutinans and F. temperatum represent closely-related maize pathogens only recently distinguished in the literature and in some cases capable of crossing in the lab. We collected genome-wide polymorphism data from a sample of both species using genotyping-by-sequencing to explore patterns of genetic divergence between the two. Our analysis supports the separation of these two as distinct species, with multiple methods consistently placing individuals into species groups, and no individuals identified as clear hybrids. Our data were characterized by high levels of both fixed differences and shared polymorphisms between species. Demographic modeling to fit the joint allele frequency spectrum supported a model with gene flow between species subsequent to their split. It also indicated that this gene flow has been biased into F. temperatum. By investigating the genome-wide distribution of the fixed differences and shared polymorphisms between these species, we cannot pinpoint discrete regions that may have been critical in speciation. However, we find an enrichment of shared polymorphisms between species at the chromosome ends. This pattern raises interesting questions about the interaction between natural selection and gene flow during the divergence of these species. Comparing the genetic diversity and evidence for population structure within each species, we found more evidence for genetic structure within F. temperatum. This species was also found at higher elevation and was associated with more ancient maize varieties, potentially indicating less adaptation to modern agricultural practices.