The influence of environmental heterogeneity on the morphological and genetic diversity of Circaea lutetiana (Onagraceae) in Hyrcanian forests

Abstract

Environmental gradients are important factors that can potentially influence the genetic diversity and differentiation of populations. The present study examines the effect of environmental heterogeneity of the Hyrcanian forests on populations of Circaea lutetiana L. (Onagraceae). Using morphometrics, scanning electron microscopy (SEM) of leaf epidermis, and molecular markers, we analyzed genetic diversity and differentiation among nine populations from environmentally divergent habitats. Three different gene pools were observed. Our results indicate that the genetic structure is significantly correlated to environmental factors, but not to the geographical distance. Genetic clustering in C. lutetiana is affected by temperature, humidity, elevation, and average annual rainfall. Overall, our data indicate that gene flow does not contribute to explaining spatial patterns of genetic structure and the adaptation to the environment is the main factor shaping the genetic structure of the C. lutetiana populations. The populations belonging to each of the three gene pools have similarities in microclimate parameters, despite their geographical proximity, and populations from the same genetic pool can be up to 470 km apart. This evidence, as well as morphological and genetic similarities of the populations with greater geographical distance, suggest the possibility of cryptic speciation in this species.