What does it mean to be an educated person?
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What does it mean to be an educated person?

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“What does it mean to be an educated person?” As part of a college-wide discussion, students were invited fall semester to participate in an essay contest to address the question of what makes an “educated person.” A total of 67 entries were received. Below are the winning essays of six students. If you have questions or comments about the contest or the content of the essays, contact Vermont Tech's Academic Affairs Office at (802) 728- 1311.
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Silva Fennica 45(4) research articlesSILVA FENNICA
www.metla.f/silvafennica · ISSN 0037-5330
The Finnish Society of Forest Science · The Finnish Forest Research Institute
Phylogeographic Pattern of Populus
cathayana in the Southeast of Qinghai-
Tibetan Plateau of China Revealed by
cpSSR Markers
Youhong Peng and Ke Chen
Peng, Y. & Chen, K. 2011. Phylogeographic pattern of Populus cathayana in the southeast
of Qinghai-Tibetan Plateau of China revealed by cpSSR markers. Silva Fennica 45(4):
583–594.
The vegetation in the Qinghai-Tibetan Plateau is thought to be highly sensitive and more
vulnerable to global climate change than that of other areas. The uplift of the plateau as well
as the climatic oscillations during glacial periods had a profound impact on plant species
distribution and genetic diversity there. In the present study, seven pairs of cpSSR (chloro-
plast Simple Sequence Repeat) primers were utilized to detect genetic varieties of Populus
cathayana Rehd populations from their natural range in the southeastern areas of Qinghai-
Tibetan Plateau. A total of 28 alleles and 12 different haplotypes were detected. The proportion
of haplotype variation among populations (G = 0.794, N = 0.900) indicated high level ST ST
of genetic differentiation among and a signifcant phylogeographic structure
(N > G , P < 0.05). This appears to support the hypothesis that these populations were ST ST
derived from multiple refugia areas during the Quaternary climatic oscillations. Based on the
haplotype network and mismatch distribution analyses, we found no evidence of postglacial
range recolonization and expansion by P. cathayana in this region. This might be mainly
due to the complex topography of the southeastern part of the Qinghai-Tibetan Plateau. The
lofty mountain ranges and deep valleys in this region might have prevented long-distance
migrations of this species during the climatic amelioration.
Keywords genetic differentiation, refugia, phylogeography
Addresses Chinese Academy of Sciences, Chengdu Institute of Biology, Chengdu, China
E-mail pengyh@cib.ac.cn
Received 23 November 2009 Revised 28 July 2011 Accepted 7 September 2011
Available at http://www.metla.f/silvafennica/full/sf45/sf454583.pdf
583Silva Fennica 45(4), 2011 research articles
to be regarded as one of the largest “biodiversity 1 Introduction
hotspots” in the world (Myers et al. 2000).
Glaciations had important effects on the pat-
The Qinghai-Tibetan Plateau is the largest and terns of spatial distribution and genetic struc-
highest plateau of the world, covering approxi- ture of species (Avise 1998, Hewitt 2000, 2004).
6 2mately 2.5×10 km (Zheng 1996). Its uplift has Analyzing glacial refugia and postglacial rec-
profoundly impacted Chinese geomorphic pat- olonization patterns can help to reveal historic
terns and climate, bringing about a series of eco- events and improve understanding the phylogeo-
environmental consequences (Zhang et al. 2000). graphic pattern of species (Walter and Epperson
For example, its uplift changed the atmospheric 2001, Richardson et al. 2002, Cuenca et al. 2003,
circulation of wind systems, adjusted the trans- Gómez et al. 2005). Although in the southeast of
port of water vapor and heat and developed the Qinghai-Tibetan Plateau, specifc geological fac-
East Asian and South Asian monsoon (An et al. tors (especially the Quaternary glaciations) have
1991). The unique ecological characteristics of signifcantly shaped the present-day distribution
this plateau have lead to vegetative communities and diversity of many species. Using chloroplast
which are thought to be highly sensitive and more DNA sequence variation, Zhang et al. (2005)
vulnerable to global climate change than that of found that the northeast edge of the Qinghai-
other areas (Thompson et al. 1994, Zhang et al. Tibetan Plateau was likely a large refugium for the
1996, Ni 2000). endemic Juniperus przewalskii (Cupressaceae)
The large-scale uplift of the Qinghai-Tibetan during the last glacial period and that J. przew-
Plateau was an important geological event in the alskii of the plateau platform is probably derived
Quaternary period. The uplift formed a natural from a recent colonization. Studies on Ginkgo
division between the temperate and subtropical biloba using chloroplast DNA (cpDNA) also
zones of mainland China. Consequently, South- found that refugia of this species were located
west China was less affected by cold air from in the southwest China, but detected no recent
Siberia during the glaciations. According to pollen long-distance dispersal and population expan-
fossil records and biological evidence, the uplift sion (Shen et al. 2005). Few other studies about
and climatic oscillations of Quaternary period glacial refugia and postglacial recolonization have
profoundly impacted biome shifts (Zhang et al. been carried out with a focus on the species in
2000, Sun 2002). This event was characterized this region.
by migration of the northerly biome from north The species of the genus Populus L. (Sali-
to south into the glacial region and the south- caceae), collectively known as poplars, are widely
ern biome northward into the interglacial region. distributed in the forests of the Qinghai-Tibetan
In the Qinghai-Tibetan Plateau, especially in its Plateau. The distribution and differentiation of this
southern and eastern areas, many huge moun- genus appear to have been profoundly infuenced
tains run south to north, with basins, rivers and by the glacial periods (Yu et al. 2003). In the
other geomorphic units on the surface. During the present study, we employed molecular markers
Quaternary glaciations, when the northerly biome to analyze the genetic relationships and genetic
was gradually receding from north to south, the structure of Populus cathayana Rehd populations
southeast region of the Qinghai-Tibetan Plateau from the southeast of Qinghai-Tibetan Plateau.
provided refugia for this biome. Fossil records of Populus cathayana is a native species of China
many species (i.e., Picea, Abies, Populus, Gink- and it belongs to Sect. Tacamahaca Spach. It is
gos and Metasequoia) also revealed that this found along a large geographic range, but mainly
region was an important refugium for species occurs in the northern, southwestern and central
that survived the Quaternary glaciations (Wang parts of China (Wu and Raven 1994). In the south-
and Liu 1994). Because of its role as an important ern and eastern areas of Qinghai-Tibetan Plateau,
refugium during the glacial periods, the south- many P. cathayana occur in the mountains and
eastern region of the Qinghai-Tibetan Plateau of canyon belts between the plateau and plain at
China is extremely rich in species (Tang and Shen altitudes varying between 1500–3900 m above
1996). This species richness had led the plateau sea level (Zhao and Gong 1991). A large amount
584Peng and Chen Phylogeographic Pattern of Populus cathayana in ... China Revealed by cpSSR Markers
Table 1. The ecological and geographical parameters of the P. cathayana populations sampled.
Population Landform feature Water system Longitude Latitude Altitude Annual Annual Warmest Sample
(E) (N) (m) rainfall mean month size
(mm) temp (ºC) (ºC)
SHY Riparian and basin Dadu river 102º40’ 29º25’ 1500 750 17.7 22.0 29
JZ Alpine and canyon Bailong river 103º57’ 32º13’ 1600 553 12.7 16.8 21
PW Canyon and basin Peijing river 104º25’ 32º01’ 1620 566 14.7 18.1 18
QHY Plateau and mountain Huangshui river 100º23’ 37º54’ 3100 412 3.3 11.5 28
LD ver 102º28’ 36º31’ 3160 335 6.9 13.4 28
TS Canyon and basin Wei river 105º40’ 34º37’ 1650 531 11.5 22.6 17
of genetic diversity has been revealed by previ- 2 Materials and Methods
ous studies on this species (Peng et al. 2005, Lu
et al. 2006). This diversity could be exploited for 2.1 Plant Materials
conservation, breeding programs and afforesta-
tion schemes. A total of 144 individuals from six natural popu-
Molecular markers, in particular organelle lations of P. cathayana were collected from the
genome (cpDNA and mtDNA) markers have southern and eastern areas of Qinghai-Tibetan
proven powerful in identifying refugia and Plateau in China. Three (SHY, JZ, PW) of the
tracking colonization routes, because organelle six sampled populations were from the Sichuan
genomes are inherited without recombination province. Two of the populations (QHY, LD)
(Newton et al. 1999, Caron et al. 2000, Petit et were from the Qinghai province and one (TS)
al. 2003). In general, chloroplast genomes show was from the Gansu province. These populations
low levels of nucleotide variation below the spe- were chose to represent the various climates and
cies level (Schaal et al. 1998). Chloroplast Simple topographies over which P. cathayana of the
Sequence Repeats (cpSSR) is most suitable for use southeastern areas of Qinghai-Tibetan Plateau
in intraspecifc studies because this technique ena- is naturally distributed (Table 1) (Fig. 1). For
bles detection more variation than possible using each of the natural populations, individual cut-
other molecular markers (e.g., RFLPs) (Powell et tings separated by a distance of more than 50 m
al. 1995

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