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

M.V. FUMERO; W. YUE; M.L. CHIOTTA; S. CHULZE; LESLIE J.F.; TOOMAJIAN C.

Pacific Grove, California

Congreso; 30th Fungal Genetics Conference; 2019

Genetics Society of America

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 it implies for adaptive evolution, especially in pathogenic species. Fusarium subglutinans and F. temperatum represent closely-related maize pathogens only recently distinguished based on molecular phylogenies, but which, in some cases, can cross sexually in the lab. We generated genome-wide polymorphism data from a sample of both species to explore patterns of genetic divergence between the two. Our analysis supports the separation of these two entities as distinct species, with multiple methods consistently placing individuals into species groups, and no individuals identified as clear hybrids. Demographic modeling to fit the joint allele frequency spectrum from both species supported a model with gene flow between species subsequent to their split. It also estimated that gene flow was much more substantial from F. subglutinans into F. temperatum than in the opposite direction. Our data included high numbers of fixed differences between species, but their genome-wide distribution did not reveal discrete regions that may have been critical in speciation. Shared polymorphisms between species were enriched at the chromosome ends, a pattern that raises interesting questions about the interaction between natural selection and gene flow during the divergence of these species. Levels of genetic diversity in each species were similar, but population structure was more evident in F. temperatum. This species also was foundat higher elevation and in association with more ancient maize varieties, potentially indicating less adaptation to modern agricultural practices.