Can pollinators track plant expansions? A case study on the genetic structure of a host-dependent pollinating wasp

Plants and their pollinators may respond differently to environmental changes like climate warming. As a consequence, whether the pollinators can successfully track the migration of the plants and rebuild an effective pollinator network are crucial for mutualistic relationships, especially obligate mutualisms. Ficus altissima is a commonly planted tree out of its native range, providing an opportunity to determine if its obligatory pollinating wasp species, Eupristina altissima, can track the range expansion of its host. Using mtDNA COI gene, we found that E. altissima is the only pollinator species at introduced sites of F. altissima, thereby confirming that this specific pollinator can track the range expansion of its host fig tree. However, population genetic analysis using both COI gene and microsatellite markers detected a significant reduction in genetic variation (number of mtDNA haplotypes and microsatellite-based genetic diversity indices) and an enhanced differentiation among populations within the expanded distribution range. These findings are consistent with the consequences of founder events. Our findings suggest that plant range expansion caused by artificial introduction may not suffer from loss of pollinators as previously expected, even within the extremely obligate mutualisms such as the fig-fig wasp system, when pollinators can disperse, actively or passively, over long distances.