How to be a fig nematode

Abstract

Fig (Moraceae: Ficus) species host vast communities of organisms that are bound together by complicated ecological networks that have influenced community structure and dynamics over evolutionary timescales. Much attention has been paid to the mutualism between figs and their specialized pollinating fig wasps, as well as with often antagonistic non-pollinating fig wasps. Equally ubiquitous to fig systems, but much less understood are the multitude of nematode groups that have independently evolved obligate associations with pollinating fig wasps and proliferate inside fig syconia. In this review we describe what is currently known (and unknown) about these numerous and increasingly studied nematode taxa and how they interact with the fig systems they inhabit. We identify the groups that are currently understood to associate with fig pollinators and outline their known species distributions and evolutionary history, where possible. Special attention is paid to the life history of these nematode groups, especially which features of nematode biology are generalizable across groups and what idiosyncratic peculiarities exist within individual genera. We outline key biological features including host choice, dispersal, disembarkation, diet, mating, and proliferation within figs. We address biological conundrums that have been raised following observational work such as, why do nematodes sometimes infect the wrong host? What adaptations were required for nematodes to successfully adapt and coexist with figs and their pollinators for millions of years? How do nematodes overcome the constraints of low mating group size? Finally, we outline key considerations, gaps in the knowledge, and limitations to expand this field forward towards promising areas of future research. Through better understanding of fig nematodes, we stand to not only know more about Ficus communities, but also more about the evolution and maintenance of interspecific interactions, development, adaptation, and co-evolution in general.