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Strong spatial‐genetic congruence between a wood‐feeding cockroach and its bacterial endosymbiont, across a topographically complex landscape

Garrick, Ryan C., Sabree, Zakee L., Jahnes, Benjamin C., Oliver, Jeffrey C.
Journal of biogeography 2017 v.44 no.7 pp. 1500-1511
Blattabacterium, Cryptocercus darwini, Cryptocercus punctulatus, biogeography, endosymbionts, insects, intergenic DNA, landscapes, mitochondrial genes, nucleotide sequences, phylogeny, screening, sequence diversity, symbiosis, topography, topology, Appalachian region, United States
AIM: We analysed data from an insect host (Cryptocercus punctulatus) and its maternally‐inherited obligate bacterial endosymbiont (Blattabacterium cuenoti str. punctulatus) to address the following: (1) to what extent do these species exhibit cophylogenetic structure, (2) do the spatial‐genetic structures of these species differ, and (3) what is the relative importance of codivergence versus other events in explaining congruence, or instances of incongruence, between their molecular phylogenies? LOCATION: The southern Appalachian Mountains, USA. METHODS: We conducted fine‐scale population‐level sampling and screening of DNA sequence variation in two mitochondrial genes from the host, and four genic or intergenic regions from the endosymbiont. Inferences were made using analyses that have the potential to identify isolated instances of cophylogenetic discord, uncover subtle differences in geographic locations of genetic discontinuities, and disentangle different evolutionary processes that contributed to observed patterns. RESULTS: The host and its endosymbiont showed similar phylogenetic and geographic patterns. Cophylogenetic analyses revealed that while topological discord is rare (and restricted within major clades), some instances are potentially non‐negligible. Assessments of spatial‐genetic structure showed that most abrupt breaks occur in the same locations, but they differ in strength, again underscoring some subtle discordance. The main process generating observed patterns was inferred to be codivergence due to host‐tracking; however, incomplete lineage sorting seems likely to have also played a minor role. MAIN CONCLUSIONS: Our overarching finding of strong congruence is reflected by broader‐scale cophylogenetic studies of related Cryptocercus and Blattabacterium taxa. Accordingly, we suggest that members of this symbiosis may provide an excellent opportunity for investigating geographic scaling of processes that affect biogeographic patterns. However, fine‐scale sampling coupled with geospatial analyses detected rare and/or minor discordances that appeared to be localized within the most deeply dissected topographic regions of the southern Appalachian Mountains, and these warrant further exploration.