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: 1.66). 02/2012; 172. 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.

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    ABSTRACT: A well-dated suite of Lake Van climate-proxy data covering the last 360 ka documents environmental changes over 4 glacial/interglacial cycles in Eastern Anatolia, Turkey. The picture of cold and dry glacials and warm and wet interglacials emerging from pollen, organic carbon, authigenic carbonate content, elemental profiling by XRF and lithological analyses is inconsistent with classical interpretation of ox-ygen isotopic composition of carbonates pointing to a more complex pattern in Lake Van region. Detailed analysis of glacial terminations allows for the constraining of a depositional model explaining different patterns observed in all the proxies. We hypothesize that variations in relative contribution of rainfall, snowmelt and glacier meltwater recharging the basin have a very important role for all sedimentary processes in Lake Van. Lake level of glacial Lake Van, predominantly fed by snowmelt, was low, the water column was oxic, and carbonates precipitating in the epilimnion recorded the light isotopic signature of inflow. During terminations, increasing rainfall and significant supply of mountain glaciers' meltwater contributed to lake level rise. Increased rainfall enhanced density gradients in the water column, and hindered mixing leading to development of bottom-water anoxia. Carbonates precipitating during terminations show large fluctuations in their isotopic composition. Full interglacial conditions in Lake Van are characterized by high or slowly falling lake level. Rainfall and snowmelt feed the lake but due to re-established mixing, the isotopic composition of authigenic carbonates is heavier and closer to that of evaporation-influenced lake water than that of runoff representing snowmelt and atmospheric precipitation.
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    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.
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