Population genetics methods applied to a species delimitation problem: Endemic trumpet daffodils (Narcissus section pseudonarcissi) from the southern Iberian Peninsula

Abstract

Premise of research. Determination of species boundaries is essential for understanding and preserving biological diversity, yet it remains a difficult task for many plant lineages. Population genetics approaches explicitly taking into account the geographic context of processes driving population divergence and speciation may help to identify species boundaries in complex groups. Here, we adopt this approach to investigate genetic boundaries in an endemic group of trumpet daffodils (Narcissus, section Pseudonarcissi) whose taxonomic distinctiveness remains controversial. Methodology. We analyzed amplified fragment length polymorphism markers from a total of 36 populations (526 individuals) spanning the group'S entire distribution range in the southern Iberian Peninsula. To identify the most likely number of distinct genetic groups, model- and nonmodel-based methods (Bayesian, principal coordinates, and neighbor-joining classification) were applied. Effects of long-term historical divergence were dissected from more recent or local differentiation processes using simple and partial Mantel tests. Pivotal results. A major genetic split, consistently supported by the three analytical methods used, differentiated all populations generally ascribed to Narcissus bujei in traditional taxonomic treatments from the rest, which included all populations generally designated as Narcissus longispathus and Narcissus nevadensis. The two groups exhibited contrasting levels of within-population genetic diversity and rarity. Comparative analyses of the relationship between genetic differentiation and geographic distance in these two main genetic lineages suggested that they have remained isolated through a long time period. Separate analyses of genetic and geographic patterns within each major lineage suggested contrasting evolutionary histories. Conclusions. Genetically, geographically, and ecologically well-defined lineages of the Pseudonarcissi section occur throughout the southern mountains of the Iberian Peninsula, generally supporting the traditional taxonomical delimitation of this lineage and qualifying as separate units of conservation. Our findings emphasize the usefulness of molecular data and population genetics approaches in a geographic context to delineate morphologically cryptic species in complex lineages. © 2014 by The University of Chicago. All rights reserved.