Ant-infecting Ophiocordyceps genomes reveal a high diversity of potential behavioral manipulation genes and a possible major role for enterotoxins

Abstract

Much can be gained from revealing the mechanisms fungal entomopathogens employ. Especially intriguing are fungal parasites that manipulate insect behavior because, presumably, they secrete a wealth of bioactive compounds. To gain more insight into their strategies, we compared the genomes of five ant-infecting Ophiocordyceps species from three species complexes. These species were collected across three continents, from five different ant species in which they induce different levels of manipulation. A considerable number of (small) secreted and pathogenicity-related proteins were only found in these ant-manipulating Ophiocordyceps species, and not in other ascomycetes. However, few of those proteins were conserved among them, suggesting that several different methods of behavior modification have evolved. This is further supported by a relatively fast evolution of previously reported candidate manipulation genes associated with biting behavior. Moreover, secondary metabolite clusters, activated during biting behavior, appeared conserved within a species complex, but not beyond. The independent co-evolution between these manipulating parasites and their respective hosts might thus have led to rather diverse strategies to alter behavior. Our data indicate that specialized, secreted enterotoxins may play a major role in one of these strategies.

A genome scan of diversifying selection in Ophiocordyceps zombie‐ant fungi suggests a role for enterotoxins in co‐evolution and host specificity

“…We also investigated whether the genes previously identified as encoding possible “neuromodulators” (de Bekker et al., ), based on their overexpression during the manipulation of ant behaviour, showed signs of positive selection. In total, 12 to 41 of these genes yielded significant results in tests for positive selection (Supporting Information Table ).…”

“…In addition to the predicted proteins from the de novo assembled and improved genomes of O. unilateralis species from Thailand, we also included in our analyses the predicted proteins of other ant‐infecting Ophiocordyceps fungi specific to different ant species and originating from different geographic areas (de Bekker et al., ). We used the available genomes from two additional O. unilateralis s.l .…”

“…We used the available genomes from two additional O. unilateralis s.l . species (O. kimflemingiae from the United States and O. camponoti‐rufipedis from Brazil), from two cryptic species of O. australis s.l., from Ghana and Brazil (de Bekker et al., ), and from O. subramanianii s.l., also from Ghana. The predicted proteins corresponding to all these genomes were subjected to Blast comparisons with each other, with a significance threshold e‐value of 1e −5 .…”

“…We sequenced the genomes of two closely related species of the O. unilateralis complex from Thailand: O. camponoti‐leonardi and O. camponoti‐saundersi, specific to the ants Colobopsis leonardi and C. saundersi, respectively. We also improved the available genome assembly of another species of this complex, O. polyrhachis‐furcata, specific to Polyrhachis furcata (Wichadakul et al., ), and used the published genomes of other ant‐infecting Ophiocordyceps species (de Bekker et al., ): one genome of each of two species of O. unilateralis s.l., O. kimflemingiae from the United States infecting Camponotus castaneus (Araújo et al., ; de Bekker et al., ) and O. camponoti‐rufipedis from Brazil specific to C. rufipes (Araújo et al., ; Evans et al., ); one genome of O. subramanianii s.l . from a ponerine ant in Ghana; one genome of each of two strains of O. australis s.l .…”

“…from a ponerine ant in Ghana; one genome of each of two strains of O. australis s.l . found on different ponerine ant species, from Ghana and Brazil, probably belonging to different cryptic species (de Bekker et al., ).…”