Genetic structure of Ipomoea imperati (Convolvulaceae) in the Mediterranean region and implications for its conservation

Abstract

In this paper, we studied the relationships of the only surviving Italian population of Ipomoea imperati (Convolvulaceae), a pantropical sandy coastal species, in Sicily and other populations in the Mediterranean region. Herbarium samples which are representative of extinct populations growing  in Campania (Italy) were also investigated together with populations from various Atlantic and Mediterranean localities. Chloroplast DNA microsatellites (cp-SSR) and nuclear ribosomal Internal Transcribed Spacer (ITS) sequences  were jointly employed, in order to detect relationships among populations. Our aims were several-fold: (1) to clarify if the species is autochthonous in the Mediterranean basin or a post-Columbian introduction; (2) to investigate phylogeographic patterns in the species and (3) to establish the possible role of dispersal in explaining the patterns observed. Chloroplast microsatellite variation indicates that extinct Italian mainland populations of I. imperati from Campania are not closely related to the extant Sicilian one, as they do not share haplotypes. Chloroplast DNA microsatellite variation is largely between populations, and the within populations component accounts for only approximately 10%. CpDNA data is consistent with a single Mediterranean entry point hypothesis or with the notion that some populations display plesiomorphic variability. ITS data is congruent with the possibility that the presence of I. imperati in the Mediterranean is the result of transatlantic dispersal. The population from Sicily and extinct populations from Campania share an ITS type. A Bayesian analysis employing clock calibration data on an expanded ITS dataset with appropriate outgroups indicates that dates of transoceanic distribution are probably earlier than historical times.