Detecting signatures of discordant population structure and local adaptation in a codiversifying host-obligate endosymbiont mutualism



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To investigate the landscape-level effects on a host-obligate endosymbiont mutualism, we performed whole-genome sequencing on the ant host Camponotus modoc and its obligate endosymbiont, Blochmannia. C. modoc is widely distributed in the western United States, experiencing a range of environmental selective pressures as well as varying potential barriers to gene flow, enhancing the possibility of genetic differentiation throughout the geographic range. While it has been demonstrated that these organisms are codiversifying, the genetic effects on both organisms have not been explored in detail. Specifically, the presence of coevolution has not been tested in this mutualism. Here, we investigate how the landscape is affecting population structure between hosts and endosymbionts, and test for signatures of local adaptation and whether these signatures could be driving coevolution. We find evidence of discordant population structure in this obligate mutualism and signatures of local adaptation in both organisms, with a positive correlation between the environmentally correlated loci and genetic distances of C. modoc and Blochmannia. We also find evidence of host lineage switching in Blochmannia, as three of our samples were likely the result of introgression from another Camponotus species. The discordant population structure is likely a result of differing patterns of male and female dispersal and gene flow in C. modoc, as the Blochmannia is maternally transmitted. Overall, we find that the landscape is playing a role in shaping genetic differentiation and local adaptation in this obligate mutualistic interaction. Further work is needed to demonstrate that coevolution is occurring and to determine the functional role that the environmentally correlated loci we identified here are responsible for between C. modoc and Blochmannia.



Landscape Genomics, Endosymbiosis