Predicting distributions of Wolbachia strains through host ecological
contact -- who's manipulating whom?
Abstract
Barriers to gene-flow within populations, typically in response to
divergent selection, are often mediated via third-party interactions.
Under these conditions speciation is inextricably linked to ecological
context. We present a novel framework for studying arthropod speciation
as mediated by Wolbachia, a microbial endosymbiont capable of causing
host cytoplasmic incompatibility (CI) via alternative strain
associations. Building on empirical findings, our model predicts that
sympatric host sister-species harbour paraphyletic strains that provide
CI, while well-defined congeners in ecological contact and recently
diverged noninteracting congeners are uninfected due to Wolbachia
redundancy. We argue that Wolbachia may provide an adaptive advantage
when coupled with reduced hybrid fitness (via trait mismatching), by
facilitating assortative mating between co-occurring divergent
phenotypes – the contact contingency hypothesis. To test this, we
applied a custom-built predictive algorithm to empirical data from
host-specific pollinating fig wasps, achieving ≤88.46% accuracy. We
then considered post-zygotic offspring mortality during CI matings by
developing a model featuring fitness clines across oviposition
resources. This oviposition trade-off model, tested through simulation,
favoured CI at realistic conspecific mating frequencies despite
fecundity losses. We demonstrate that a rules-based algorithm accurately
predicts Wolbachia infection status. This has implications among other
systems where closely-related sympatric species encounter adaptive
disadvantage through hybridisation.