Consistent patterns of fungal communities within ant-plants across a
large geographic range strongly suggest a multipartite mutualism
Abstract
In recent decades, multipartite mutualisms involving microorganisms such
as fungi have been discovered in associations traditionally thought of
as bipartite. Ant-plant mutualisms were long thought to be bipartite
despite fungi being noticed in an epiphytic ant-plant over 100 years
ago. We sequenced fungal DNA from the three distinct domatium chambers
of the epiphytic ant-plant Myrmecodia beccarii Hook.f. to establish if
fungal communities differ by chamber type across five locations spanning
675 km. The three chamber types serve different ant-associated functions
including: ‘waste’ chambers, where ant workers deposit waste; ‘nursery’
chambers, where the brood are kept; and ‘ventilation’ chambers, that
allow air into the domatium. Overall, fungi from the order
Chaetothyriales dominated the chambers in terms of the proportion of
OTUs (13.4%) and sequence abundances of OTUs (28% of the total),
however a large portion of OTUs (28%) were unidentified at the order
level. Notably, the fungal community in the waste chambers differed
consistently from the nursery and ventilation chambers across all five
locations. We identified 13 fungal OTUs as ‘common’ in the waste
chambers that were rare or in very low sequence abundance in the other
two chambers. Fungal communities in the nursery and ventilation chambers
were also significantly different, but variation between these chambers
was less pronounced. Differences in dominance of the common OTUs drive
the observed patterns in the fungal communities for each of the chamber
types. This suggests a multipartite mutualism involving fungi exists in
this ant-plant and that the role of fungi differs among chamber types.