Assessing symbiont extinction risk: insights from host-symbiont cophylogenetics and coevolutionary theory

Symbionts (i.e., parasites, mutualists, and commensals that interact intimately with their hosts) have a unique mode of life that has attracted the attention of ecologists and evolutionary biologists for centuries. As a result of this attention, these disciplines have produced a mature body of literature on these interactions. In contrast, the discipline of symbiont conservation is still in a foundational stage. Further, given the particularities of the life-history of symbiont species, some problems may arise when directly applying knowledge from Conservation Biology of free-living species to symbiont conservation. Here, we aim to adapt existing ecological and evolutionary knowledge of symbionts to the perspective of biological conservation. Specifically, we first propose a new statistic “cophylogenetic extinction rate” (Ec) that uses data from event-based cophylogenetic analyses and might be informative to assess relative symbiont extinction risks. Then, we outline aspects of ecology or evolution that may be relevant to consider for assessing symbiont vulnerability to extinction. Finally, we propose potential future research to further develop estimation of symbiont extinction risk from cophylogenetic analyses and continue the integration of this existing knowledge into future symbiont conservation studies and practices.