Article

Ecological implications of Cousinia Cass. (Asteraceae) persistence through the last two glacial-interglacial cycles in the continental Middle East for the Irano-Turanian flora.

Review of Palaeobotany and Palynology (Impact Factor: 1.93). 01/2012; DOI: 10.1016/j.revpalbo.2012.01.005

ABSTRACT This study explores the response of the Irano-Turanian flora to Quaternary glacial–interglacial cycles in SW Asia. We use new fossil pollen data to assess variation in abundance of Cousinia Cass. (Compositae), a large genus typical for the Irano-Turanian flora, during these cycles. The results are compared with modern topography, tectonic and palaeoclimatic history, and recent phylogenetic data to explain the extremely high speciation rate and level of endemism as well as the modern geographical distribution of the genus. Cousinia is consistently well-represented in glacial-age and late-glacial pollen assemblages of NW Iran and E Anatolia. In the ~ 200,000-year pollen sequence from Lake Urmia, NW Iran, Cousinia pollen shows significant values and is nearly continuously represented during both the last glacial (~ 70 ka to Holocene) and penultimate glacial periods (~ 190 to 130 ka). In contrast, its pollen is less frequent and occurs only sporadically during the last interglacial period and the Holocene. This pattern suggests that Cousinia could not only withstand Quaternary glaciations, but was a significant part of the glacial-age landscapes of the Irano-Turanian territory. We argue that the extremely high rate of speciation and endemism of Cousinia is due to (i) the continuous presence of a complex topography in the Middle East and Central Asia since Tertiary times, which created a wide range of environmental niches and facilitated the formation and persistence of isolated populations over long periods, (ii) relatively stable climate during the late Miocene–Pliocene compared to the Quaternary period that caused small species range shifts and gene flow, and (iii) a dampened impact of multiple glacial–interglacial cycles on the mountain regions of SW Asia compared to the higher latitude European mountain ranges. This left an extensive, non-glaciated altitudinal zone for the survival of Irano-Turanian species, thereby reducing extinction during glacial periods. During interglacial periods, many Cousinia species may have been geographically isolated in high mountain “interglacial refugia” of the Irano-Turanian region. Overall, the combination of the above factors during the Neogene resulted in geographical isolation and reduced gene flow, thereby fostering allopatric speciation in Cousinia and probably also in many other speciose Irano-Turanian plant taxa.

1 Bookmark
 · 
308 Views
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Pollen and dinoflagellate cysts have been analysed in a core from the south basin of the Caspian Sea, providing a picture of respectively past vegetation and water salinity for the Late Pleistocene to middle Holocene. A relatively sharp lithological change at 0.86 m depth reflects a shift from detrital silts to carbonates-rich fine silts. From this depth upwards, a Holocene chronology is built based on ten radiocarbon dates on ostracod shells and bulk carbonates. From the vegetation point of view, the Late Pleistocene deserts and steppes were partially replaced in the most sheltered areas by an open woodland with Pinus, Juniperus-Hippophae-Elaeagnus and even Alnus-Quercus-Pterocarya and Fraxinus, related to the Allerød palynozone. This was interrupted by the Younger Dryas palynozone when Artemisia reaches a maximum in a first instance followed by a very dry phase with only a slight return of Pinus and Quercus and the rare presence of Ulmus-Zelkova. From 11.5 to 8.4 cal. ka BP, an open landscape dominated by shrubs such as Ephedra and progressively increasing Quercus appeared. The final spread of diverse evergreen and deciduous trees is delayed and occurs after 8.4 cal. ka BP. It is suggested that this delay is caused by an arid climate in the Early Holocene linked to high insolation and perhaps to a lake effect. The dinocyst assemblages fluctuate between slightly brackish (Pyxidinopsis psilata and Spiniferites cruciformis, 7 psu and lower) and more brackish (Impagidinium caspienense, w13 psu). In the Lateglacial (Khvalynian highstand), the assemblages remained dominated by relative low salinity taxa. A late and brief increase of salinity occurred prior to 11.2 cal. ka BP associated with the Mangyshlak lowstand. It is suggested that it was caused by a brief drop in meltwater flow from both the north and the southeast (Uzboy) and a likely evaporation increase. This lowstand occurs quasi at the same time as the end of a longer lowstand in the Black Sea. The freshest waters are then inferred as having occurred between 8.4 and �4.4 cal. ka BP, linked to a connection with the Amu Darya and the melting glaciers on the Pamir Mountains. The Caspian Sea is a sensitive environment, easily perturbed by global climatic changes, such as the Allerød and Holocene warming, and the Lateglacial and Younger Dryas cooling, as well as by regional changes in its hydrography, such as shifts in the Eurasian meltwater and the Volga and Amu Darya inflows
    Quaternary Science Reviews 10/2013; 78:77-97. · 4.57 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract Aim The Irano-Turanian (IT) floristic region is characterized by high levels of endemicity. Despite its potential role as a cradle of xerophytic taxa for neighbouring areas, its biogeographical history remains poorly studied. Haplophyllum, a diagnostic element of the IT region, was used as a model to discriminate between alternative biogeographical scenarios for the evolution of the region and, more specifically, to investigate whether it served as a source of xerophytes for the colonization of the Mediterranean Basin. Location Irano-Turanian floristic region (Central Asia and West Asiatic areas) and Mediterranean floristic region (western and eastern parts of the Mediterranean Basin). Methods Three chloroplast DNA regions were sequenced in 77 accessions of Haplophyllum and 37 accessions from other subfamilies of Rutaceae. To elucidate the temporal and spatial evolution of Haplophyllum in the IT and Mediterranean regions, we performed Bayesian molecular dating analyses with four fossil constraints and ancestral range reconstructions, respectively. Results Our molecular dating and ancestral area reconstruction analyses suggest that Haplophyllum originated in the Central Asian part of the IT region during the early Eocene and started to diversify in situ during the early Oligocene, soon after the vanishing of the Tethys Ocean. Our results further imply that Haplophyllum later invaded the eastern Mediterranean Basin in the middle-to-late Miocene, concomitantly with the Paratethys Salinity Crisis and rapid palaeobiogeographical changes in the proto-Mediterranean. Finally, Haplophyllum diversified in the western Mediterranean in the early Pliocene at the end of the Messinian Salinity Crisis. Main conclusions The IT floristic region can serve as a ‘donor’ of xerophytic taxa to ‘recipient’ neighbouring regions, including the Mediterranean floristic region. The climatic/geological processes during the Miocene–Pliocene, by increasing aridity and topographic heterogeneity, facilitated range shifts and allopatric speciation in the region.
    Journal of Biogeography 08/2013; · 4.86 Impact Factor

Full-text

Download
177 Downloads
Available from
May 21, 2014