Phylogeography of Campanula fenestrellata s.l. (Campanulaceae) in the northern Adriatic

Abstract

Campanula fenestrellata subsp. fenestrellata and C. fenestrellata subsp. istriaca belong to the morphologically and phylogenetically well established amphi-Adriatic group Campanula ser. Garganicae. The two morphologically differentiated endemic taxa are distributed on the north-eastern Adriatic islands and coast. In order to study the relationships among C. fenestrellata s.l. populations and to gain insight into genetic basis of taxonomic separation established on morphology, we examined amplified fragment length polymorphisms (AFLPs) as well as nuclear and plastid DNA sequences (ITS and trnL–trnF). With the sequence data, no structure and no distinction between the two subspecies were observed. The AFLPs separated populations geographically and inferred high number of most likely clusters. The northern and the southernmost populations were assigned to uniform separate clusters indicating the longer isolation of respective populations, while the admixed populations were evident in the central area where the two taxa geographically overlap, indicating the presence of gene flow. Distinct fragmentation patterns and the existence of several temporally continuous microrefugia during the Quaternary climatic oscillations likely promoted strong genetic differentiation within the species range, while secondary postglacial contacts are reflected in observed admixture. Although the two taxa exhibited differences in ecological preferences, niche conservatism was detected. Overall, phylogeographic reconstruction of C. fenestrellata s.l. populations highlights the importance of microrefugia in shaping the intraspecific genetic variation as well as of melting-pot areas in rearranging such variation as a result of a more recent admixture.