Investigating Systematics And Host-Parasite Dynamics in Dwarf Mistletoes (Arceuthobium spp.) Using Population Genomics

Host-parasite relationships can lead to coevolutionary dynamics broadly affecting trait evolution (e.g., a coevolutionary arms race) and diversification. The nature of these dynamics in parasitic mistletoes is not well understood. Here, I investigate evolutionary processes in the genus Arceuthobium (parasitic dwarf-mistletoe) and their conifer hosts. Arceuthobium are economically and ecologically important agricultural pests. They increase forest structures by changing the host trees' growth form providing wildlife shelter. Species of Arceuthobium section campylopoda are difficult to distinguish because putative taxa overlap morphologically and phenotypically and may have complex host specificity. This study aims to identify the genus systematics through a phylogenetic species concept. I further analyze whether Arceuthobium host races are potentially characterized by host specialization and geography. I used RAD-sequencing to characterize single nucleotide polymorphisms (SNP) data from Arceuthobium taxa, sampled across their ranges in North America and Mexico from different hosts. A PCA, structure plot, phylogeny, and isolation by distance analysis were used to examine gene flow patterns and population differentiation to connect observations with species circumscription and diversification concepts. This study found no evidence of host specialization or the species' geography affecting the genetic makeup of Arceuthobium taxa. This study highlights that all the previously debated taxa within Arceuthobium section campylopoda besides A. blumeri are genetically similar enough to be deemed the same species under the phylogenetic species concept. Unexpectedly, Arceuthobium americanum, a non-debated species, was found nested within Arceuthobium section campylopoda.