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      Pollinator scarcity drives the shift to delayed selfing in Himalayan mayapple Podophyllum hexandrum (Berberidaceae)

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          Abstract

          American mayapple and Himalayan mayapple are a pair of sister species with disjunct distribution between eastern Asia and eastern North America, which the former was considered to be self-incompatible but the later to be self-compatible. We are interested in the diversification of breeding systems in the two species, particularly a usual mode of self pollination in Himalayan mayapple ( Podophyllum hexandrum) which is achieved by movement of the pistil as a previous study suggested. By contrast, our observations and flower manipulations show that delayed selfing was facilitated by petals closing and stamens moving simultaneously to contact the stigma, and bees were effective pollinators although they were few.

          Abstract

          Recent molecular phylogenetics have indicated that American mayapple (mainly self-incompatible, SI) and Himalayan mayapple, which was considered to be self-compatible (SC), are sister species with disjunct distribution between eastern Asia and eastern North America. We test a hypothesis that the persistence of this early spring flowering herb in the Himalayan region is attributable to the transition from SI to SC, the capacity for selfing in an unpredictable pollination environment. Pollinator observations were conducted in an alpine meadow with hundreds of Himalayan mayapple ( Podophyllum hexandrum Royle) individuals over 2 years. To examine autogamy, seed set under different pollination treatments was compared. To clarify whether automatic self-pollination is achieved by movement of the pistil as a previous study suggested, we measured incline angles of the pistil and observed flower movement during anthesis using video. Floral visitors to the nectarless flowers were very rare, but solitary bees and honeybees could be potential pollinators. Seed set of bagged flowers was not significantly different from that of open-pollinated, self- or cross-pollinated flowers. However, removal of petals or stamens lowered seed yield. The angles of inclination of pistils did not change during the process of pollination. Automatic self-pollination was facilitated by petals closing and stamens moving simultaneously to contact the stigma. Stigmatic pollen load increased little during the day time, in contrast to a sharp increase when the flowers closed during the night-time. These observations indicated that Himalayan mayapple was SC and delayed self-pollination was facilitated by the movement of petals rather than the pistil. Compared with SI American mayapple, no obvious inbreeding depression in SC Himalayan mayapple may contribute its existence in the uplifting zone. A scarcity of pollinators may have driven the shift to delayed selfing in P. hexandrum.

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          Evolution of Asian monsoons and phased uplift of the Himalaya-Tibetan plateau since Late Miocene times.

          The climates of Asia are affected significantly by the extent and height of the Himalayan mountains and the Tibetan plateau. Uplift of this region began about 50 Myr ago, and further significant increases in altitude of the Tibetan plateau are thought to have occurred about 10-8 Myr ago, or more recently. However, the climatic consequences of this uplift remain unclear. Here we use records of aeolian sediments from China and marine sediments from the Indian and North Pacific oceans to identify three stages of evolution of Asian climates: first, enhanced aridity in the Asian interior and onset of the Indian and east Asian monsoons, about 9-8 Myr ago; next, continued intensification of the east Asian summer and winter monsoons, together with increased dust transport to the North Pacific Ocean, about 3.6-2.6 Myr ago; and last, increased variability and possible weakening of the Indian and east Asian summer monsoons and continued strengthening of the east Asian winter monsoon since about 2.6 Myr ago. The results of a numerical climate-model experiment, using idealized stepwise increases of mountain-plateau elevation, support the argument that the stages in evolution of Asian monsoons are linked to phases of Himalaya-Tibetan plateau uplift and to Northern Hemisphere glaciation.
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            Plant molecular phylogeography in China and adjacent regions: Tracing the genetic imprints of Quaternary climate and environmental change in the world's most diverse temperate flora.

            The Sino-Japanese Floristic Region (SJFR) of East Asia harbors the most diverse of the world's temperate flora, and was the most important glacial refuge for its Tertiary representatives ('relics') throughout Quaternary ice-age cycles. A steadily increasing number of phylogeographic studies in the SJFR of mainland China and adjacent areas, including the Qinghai-Tibetan-Plateau (QTP) and Sino-Himalayan region, have documented the population histories of temperate plant species in these regions. Here we review this current literature that challenges the oft-stated view of the SJFR as a glacial sanctuary for temperate plants, instead revealing profound effects of Quaternary changes in climate, topography, and/or sea level on the current genetic structure of such organisms. There are three recurrent phylogeographic scenarios identified by different case studies that broadly agree with longstanding biogeographic or palaeo-ecological hypotheses: (i) postglacial re-colonization of the QTP from (south-)eastern glacial refugia; (ii) population isolation and endemic species formation in Southwest China due to tectonic shifts and river course dynamics; and (iii) long-term isolation and species survival in multiple localized refugia of (warm-)temperate deciduous forest habitats in subtropical (Central/East/South) China. However, in four additional instances, phylogeographic findings seem to conflict with a priori predictions raised by palaeo-data, suggesting instead: (iv) glacial in situ survival of some hardy alpine herbs and forest trees on the QTP platform itself; (v) long-term refugial isolation of (warm-)temperate evergreen taxa in subtropical China; (vi) 'cryptic' glacial survival of (cool-)temperate deciduous forest trees in North China; and (vii) unexpectedly deep (Late Tertiary/early-to-mid Pleistocene) allopatric-vicariant differentiation of disjunct lineages in the East China-Japan-Korea region due to past sea transgressions. We discuss these and other consequences of the main phylogeographic findings in light of palaeo-environmental evidence, emphasize notable gaps in our knowledge, and outline future research prospects for disentangling the evolution and biogeographic history of the region's extremely diverse temperate flora. Copyright © 2011 Elsevier Inc. All rights reserved.
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              Self Fertilization and Population Variability in the Higher Plants

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                Author and article information

                Journal
                AoB Plants
                AoB Plants
                aobpla
                aobpla
                AoB Plants
                Oxford University Press
                2041-2851
                26 August 2013
                2013
                : 5
                : plt037
                Affiliations
                [1 ]State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University , Wuhan 430072, China
                [2 ]College of Agriculture, Henan University of Science and Technology , Luoyang, Henan 471003, China
                [3 ]College of Life Sciences, Central China Normal University, Wuhan 430079, China
                Author notes
                [* ]Corresponding author's e-mail address: sqhuang@ 123456whu.edu.cn
                Article
                plt037
                10.1093/aobpla/plt037
                4455658
                6429d807-d84f-4346-b7b8-b13c77ce101a
                Published by Oxford University Press on behalf of the Annals of Botany Company.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/3.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 13 March 2013
                : 6 August 2013
                Page count
                Pages: 8
                Categories
                Research Articles

                Plant science & Botany
                autogamy,baker's law,petal movement,podophyllum hexandrum,podophyllum peltatum,pollinator limitation,self-compatible,stigmatic pollen load.

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