Combined ecological niche modelling and molecular phylogeography revealed the evolutionary history of Hordeum marinum (Poaceae) — niche differentiation, loss of genetic diversity, and speciation in Mediterranean Quaternary refugia

Abstract

The Hordeum marinum species group consists of two annual grasses of western Eurasian saline meadows or marshes. The two grasses split in the Quaternary about two million years ago. Hordeum marinum and the diploid of Hordeum gussoneanum (2x) co-occur throughout the Mediterranean basin, while the autotetraploid cytotype of H. gussoneanum (4x) overlaps with its diploid progenitor geographically only in the utmost Eastern Mediterranean, extending from there eastwards into Asia. Using chloroplast sequences of the trnL-F region, six newly developed chloroplast microsatellite loci, ecological predictive models based on climate data, and the present geographical distribution of the two species we analysed differentiation processes in the H. marinum group. The chloroplast data indicated clear differences in the history of both species. For H. marinum we found a subdivision between genetically variable populations from the Iberian Peninsula and the more uniform populations from the remaining Mediterranean. As an explanation, we assume Pleistocene fragmentation of an earlier widespread population and survival in an Iberian and a Central Mediterranean glacial refuge. Chloroplast variation was completely absent within the cytotypes of H. gussoneanum, indicating a severe and recent genetic bottleneck. Due to this lack of chloroplast variation only the combination of ecological habitat modelling with molecular data analyses allowed conclusions about the history of this taxon. The distribution areas of the two cytotypes of H. gussoneanum overlap today in parts of Turkey, indicating an area with similar climate conditions during polyploid formation. However, after its origin the polyploid cytotype underwent a pronounced ecological shift, compared to its diploid progenitor, allowing it to colonize mountainous inland habitats between the Mediterranean basin and Afghanistan. The extant sympatric occurrence of H. marinum and H. gussoneanum 2x in the Mediterranean region is interpreted as a result of secondary contact after fast Holocene range expansion out of different ice age refugia.

Evolutionary process of Hordeum brachyantherum 6x and related tetraploid species revealed by nuclear DNA sequences

“…Chloroplast variation was completely absent within the cytotypes of H. marinum ssp. gussoneanum, indicating a severe and recent genetic bottleneck (Jakob et al 2007). Our study supports the hypothesis that H. marinum, most particularly ssp.…”

Progress in phylogenetic analysis and a new infrageneric classification of the barley genus Hordeum (Poaceae: Triticeae)

“…Analyses of loci of the chloroplast genome consistently showed taxa of the sea barley complex (H. marinum and H. gussoneanum) polyphyletic (Doebley et al 1992, Provan et al 1999, Nishikawa et al 2002, Petersen and Seberg 2003, Jakob and Blattner 2006, which contradicts traditional taxonomy and results derived from nuclear markers (Komatsuda et al 2001, Blattner 2004, Petersen and Seberg 2004, Jakob et al 2007. Moreover, the affiliation of diploid species from Central Asia were partly unclear, being either monophyletic (Doebley et al 1992, Nishikawa et al 2002 or being polyphyletic and grouping with species from the New World and from the Mediterranean (Petersen and Seberg 2003).…”

Dispersals of Hyoscyameae and Mandragoreae (Solanaceae) from the New World to Eurasia in the early Miocene and their biogeographic diversification within Eurasia

“…Besides Hyoscyameae and Mandragoreae, many other unrelated taxa have similar distribution patterns in the two regions (see review by Sun, 2002). It has been hypothesized that this distribution pattern among different Eurasian taxa could have been resulted from a common geologic or climatic event (Greuter, 1991;Jakob et al, 2007;Petit et al, 2003;Ribera and Blasco-Zumeta, 1998;Steward and Lister, 2001;Wu, 1988). Since the Cretaceous, the most remarkable physical changes of Eurasia were the retreat of Tethys Sea before Tertiary, the collision of the Indian Plate with Eurasia in early Tertiary followed by the uplift of the Himalayas and the aridification of Central Asia in the middle to late Tertiary, the connection and the breakup of Eurasia with North America through the Bering Land Bridge (BLB) and the North Atlantic Land Bridge (NALB) in the early to middle Tertiary, and the repeated advances/retreats of glaciers in the Quaternary (Barron and Peterson, 1989;Butler, 1995;Harrison et al, 1992;Lomolino et al, 2006;Tiffney and Manchester, 2001;Wen, 1999).…”