28 Minutes Later: A behavioural and transcriptomic investigation into the potential role of...
Ian Will, William C. Beckerson, Charissa de Bekker
Abstract: Coevolutionary relationships between parasites and their hosts can lead to bizarre phenotypes over time. As such, certain Ophiocordyceps fungi have evolved to manipulate the behaviour of insect and arachnid hosts. The most conspicuous examples are found in ants of the Camponotini tribe, colloquially known as “zombie ants”, which climb to elevated positions to aid fungal spore transmission. While the unusual behaviours induced during infection are well described, the molecular driving force behind these changes is still unknown. Recent genomics and transcriptomics analyses have identified several candidate secreted proteins and secondary metabolites, highly upregulated during infection. Amongst these compounds is an ergot alkaloid related to the mycotoxin aflatrem, known to cause neurological issues in cows collectively called “staggers syndrome”. Staggering is also observed in Camponotus floridanusants during the late stages of Ophiocordyceps infection and manipulation. To test if aflatrem-like compounds could be responsible for this behavioural phenotype, we injected healthy ants with purified aflatrem, and recorded their behaviour for 30 minutes. Using both the machine learning tool MARGO and manual behavioural quantification, we found that aflatrem caused reduced ant activity and speed, and increased the number and duration of staggering behaviours. To examine changes at the transcriptome level that might underlie these phenotypes, we performed RNA-Seq on the heads of aflatrem-injected ants. We identified 261 genes that were significantly up- or down-regulated in the aflatrem-injected ants compared to sham-injected controls. When compared with RNA-seq data available for ants manipulated by Ophiocordyceps camponoti-floridani, we found that 108 of these genes were also differentially regulated in the heads of late-stage Ophiocordyceps-infected ants. These shared dysregulated genes included sensory neuron membrane protein genes, several odorant-binding proteingenes, and musculoskeletal genes such as titin and obscurin. Together, these results indicate that aflatrem-like compounds, produced by O. camponoti-floridani during behavioural manipulation, significantly affect neuromuscular and sensory functioning, leading to a staggers phenotype in C. floridanus.
Keywords: Secondary Metabolites, Staggers Syndrome, Machine Learning