Reticulate evolution in nuclear Middle America causes discordance in the phylogeny of palm-pitvipers (Viperidae: Bothriechis)

Aim: A number of processes can lead to weak or conflicting phylogenetic signals, especially in geographically dynamic regions where unstable landscapes and climates promote complex evolutionary histories. The Middle American pitviper genus Bothriechis has a complex biogeographic distribution and previous phylogenetic analyses have recovered conflicting topologies based on the data type used. Here, we tested whether historic conflicts in the phylogeny were the result of reticulate evolution and whether the inferred biogeographic history of the group would enable contact among reticulate lineages. Location: Middle America. Taxon: Palm-pitvipers (genus Bothriechis). Methods: We generated a phylogenomic dataset using an anchored phylogenomics approach and inferred a genomics-based species tree and mitochondrial tree to assess incongruence among datasets. We then generated a dated phylogeny and conducted ancestral area reconstruction to examine the biogeographic history surrounding the diversification of these species. We additionally tested whether the discordance among trees is better explained by lineage sorting or reticulate evolution by testing models of reticulate evolution inferred through multiple methods. Results: We found strong support for discordance in the phylogeny of Bothriechis and corresponding evidence for reticulate evolution among lineages with incongruent placement. Ancestral area reconstruction placed these taxa in adjacent regions during the time period when reticulation was projected to take place and suggested a biogeographic history heavily influenced by vicariant processes. Main conclusions: Reticulation among geographically proximate lineages has driven apparent genomic discordance in Bothriechis and is responsible for historical incongruence in the phylogeny. Inference of the order of events suggests that reticulation among nuclear Middle American taxa occurred during a time of geologic upheaval, promoting lineage divergence and secondary contact. Reticulate evolution and similar processes can have substantial impacts on the evolutionary trajectory of taxa and are important to explicitly test for in biogeographically complex regions.