The main objective of this project will be to document the demography of speciation for both partners in a co-evolved obligate pollination mutualism (e.g. when did species split and is there ongoing gene flow?). Our study system is the fig-fig wasp mutualism, a highly diverse radiation of tropical plants in the family Moraceae pollinated by ‘species specific’ chalcid wasps.
A huge advantage of this system is that the fitness of each partner is directly linked, and relatively easy to measure: a small number of specific wasps pollinate each fig and these can be reared from discrete and enclosed units (the fig ‘fruits’). Ongoing study of figs and their pollinators along the slopes of Mt Wilhelm in Papua New Guinea is shedding light on how figs and wasps may have co-diverged (Souto-Vilaros et al., 2019). The proposed project will build on previous characterisations of population genetic structure that suggests a decoupling of speciation dynamics between mutualists driven by asymmetrical rates of speciation, wasps likely speciate much faster than figs. Our results suggest a ‘split and sort’ process of speciation (Cook and Segar, 2010) whereby incipient fig species are pollinated by multiple wasps species across a parapatric range before eventual sorting and reproductive barriers restore a one-to-one partner specificity. Subsequent work will test hypotheses relating to genic speciation in each partner, can we find highly divergent regions of the genome that may maintain reproductive isolation in the face of gene flow? Are these regions associated with key traits responsible for host choice in pollinators or volatile cues produced by hosts (Segar et al., 2019), for example?
BBSRC MIBTP and HAU
Harper Adams University