Variability, genetic structure and phylogeography of the dolomitophilous species Convolvulus boissieri (Convolvulaceae) in the Baetic ranges, inferred from AFLPs, plastid DNA and ITS sequences

Abstract

Convolvulus boissieri is an edaphic endemic plant which grows in the Baetic ranges always in association with high mountain xeric dolomitic outcrops. As these dolomitic areas appear in a ‘soil-island’ pattern, the distribution of this species is disjunct. Populations of this species frequently include a low number of individuals, which could have an important impact on their genetic diversity and viability. Convolvulus boissieri provides an excellent opportunity to study the genetic and phylogeographical aspects of species linked to dolomites. We used amplified fragment length polymorphism markers and nuclear (internal transcribed spacer region of the nuclear ribosomal cistron) and plastid sequences (trnL-trnF, rpl32-trnL and trnQ-5′rps16). Data were generated from 15 populations, representing the distribution area of the species. For sequence analysis and estimation of divergence times we also used sequences from other Convolvulus species. Results revealed low intrapopulational genetic diversity and a strong interpopulational structure. Furthermore, we found clear-cut differentiation caused by the existence of two large population groups separated by the Guadiana Menor river basin. Estimation of divergence times indicated that divergence took place during the Pleistocene glaciations. Genetic diversity and differentiation are similar to those other species exhibiting naturally fragmented distribution with a sky islands pattern. In phylogeographical terms, the successive glaciation–interglaciation cycles caused the species to spread from the western sites to eastern sites, the latter being more exposed to the effects of glaciation.