Range-wide population genetics and variation in morph ratio in style-dimorphic Narcissus papyraceus.

Abstract

• Theoretical models state that natural selection and mating patterns account for floral morph ratio in style-polymorphic plants. However, the demographic history of populations can also influence variation in morph ratios. If so, we hypothesize an association between the morph ratios and the genetic structure across populations.• We used nuclear microsatellites to assess genetic variation and structure in populations of Narcissus papyraceus, a style-dimorphic plant whose floral morph ratios (L-morph to S-morph) gradually vary throughout its distribution range in the southwestern Mediterranean Basin. We implemented analyses to relate the genetic features of populations with their morph ratios.• We found greater frequencies of the S-morph in central populations and declining frequencies toward the periphery. This geographic pattern was not associated with the genetic structure of populations. Instead, we found two distinct genetic groups, mainly separated by the Strait of Gibraltar, with a mixture of morph ratios within each one. Overall, there was a weak genetic structure. Genetic diversity was greater in central and southern dimorphic populations than in northern L-monomorphic populations.• Altogether, our results do not support the hypothesis that the demographic history of populations can account for the observed geographical pattern of morph ratios in N. papyraceus. We suggest that adaptive processes shown in previous studies in the species are the main determinant of the existing variation in the morph composition of populations.