Pronounced Genetic Separation Among Varieties of the Primula cusickiana Species Complex, a Great Basin Endemic

Abstract

Abstract— Distinguishing between populations with strong genetic structure and unique species is a common challenge in systematics, especially for taxa occurring in fragmented habitats where allopatric speciation may be widespread and distinct groups may be morphologically similar. Such is often the case with species complexes across sky island environments. In these scenarios, biogeography may help to explain the taxonomic relations between species complex members, and restriction site-associated DNA (RAD) sequencing methods are commonly used to compare closely related taxa across thousands of loci. Here we use RADseq to clarify the boundaries separating the geographically distinct but morphologically similar varieties of the Primula cusickiana species complex, and to contextualize past findings of strong genetic structure among populations within varieties. Our genetic analyses demonstrate pronounced separation between isolated populations of this Great Basin endemic, indicating that the current varietal classification of complex members is inaccurate, and emphasizing their conservation importance. We discuss how these results correspond to recent biogeographical models used to describe the distribution of other sky island taxa in western North America. Our findings also fit into a wider trend observed for alpine Primula species complexes, and we consider how edaphic specialization and heterostylous breeding systems may be contributing to frequent diversification via allopatric speciation in this genus.