No abstract

Parasites and their hosts often share intimate coevolutionary relationship that can lead to bizarre phenotypes over time. Ophiocordyceps is one such genus that has evolved to manipulate the behavior of its various insect and arachnid hosts, the clearest examples of which are found in ants of the Camponotus tribe, colloquially known as zombie ants. While the unusual behaviors induced during infection are well described, the molecular driving force behind these changes are still unknown. Recent genomic and transcriptomics analyses have identified several candidate secreted proteins and secondary metabolites highly upregulated during infection. Of particular interest amongst these compounds is an aflatrem-like ergot alkaloid related to the mycotoxin aflatrem known to cause neurological issues in other animals, issues collectively called staggers syndrome. To test if aflatrem-like compounds play a role in Camponotus floridanus manipulation, healthy ants were injected with purified aflatrem and their behavior was monitored for 30 minutes. RNA-Seq was also performed on the heads of aflatrem-injected ants to compare any changes at the transcriptomic level to data available for ants infected by Ophiocordyceps camponoti-floridani. Behavioral assay footage was analyzed using the machine learning tool MARGO, which showed a negative correlation between activity and speed, and dose of aflatrem. Behaviors were also scored manually, identifying a positive coloration between aflatrem dose and staggering behavioral phenotypes. RNA-seq discovered 262 genes significantly up or down regulated compared to sham injected ants. Of these genes, 108 were also differentially regulated in the heads of late-stage Ophiocordyceps-infected ants. Together, these results indicate that aflatrem-like compounds may play an important role during late-stages of infection by reducing activity in ants, keeping them in elevated microclimates optimal for the production and dispersal of spores.