Molecular phylogenetic analyses indicate recent divergence of two gryllid-specific lineages within the generalist entomopathogenic fungus Metarhizium pingshaense clade

This study investigated the phylogenetic position, pathogenicity, and phenotypic variation of Metarhizium isolates from the Australian cricket Teleogryllus commodus and the Japanese cricket T. emma. Molecular phylogenetic analysis revealed that both the fungal groups formed two clades within the M. pingshaense clade of the PARB clade, a lineage composed of generalist species that infect multiple orders of insects. Virulence bioassays on insects from three orders showed that both fungal groups were cricket-specific and distinctly different from closely related isolates of the PARB clade, despite the very shallow molecular phylogenetic divergence among them. The growth rates of both fungal groups on the agar medium were relatively slow, which seemed to reflect their narrow host range. PCR of virulence genes, such as DtxS1 and Mcl1, revealed that they were conserved among generalist PARB clade members but absent in both or one of the two gryllid-specialists. These results indicate that the two gryllid-specialist lineages have recently diverged from the ancestral generalist lineage, with concomitant divergence or loss of these virulence genes. This study contributes to our understanding of the evolutionary relationships between generalist and specialist species in Metarhizium.