Genetic variation in the lichens Buellia frigida and Xanthoria elegans from the Vestfold Hills, eastern Antarctica

Antarctica is a desert continent dominated by micro-organisms. The seals and penguins, which are conspicuous around its margins, depend upon the sea for their food resources and are effectively part of the marine food chain. Life depends upon the availability of free water. In Antarctica water is usually locked up in ice, only in summer is there free water in the terrestrial environment. Not only is water limited, but low temperatures and low levels of nutrients severely limit the scope for growth among the micro-organisms that have managed to colonise the continent. Propagules are brought to the continent in a number of ways. Some arrive in the air masses that flow around the Earth. Once deposited some simply cannot survive the extreme conditions, while others may become established. Other species of micro-organism may be introduced by Man around the scientific stations on the continent. During the ice-ages which have occurred repeatedly through geological history, micro-organisms may have survived in refugia offered by nunataks or in the ice, and have recolonised more widely following ice retreat.This project will concentrate on one group of micro-organisms, the fungi. We will use special air samplers to determine which species are brought to the continent in the winds and we will compare the propagules from these samplers with the species living in the 'soil' and samples grown up from ice samples, where the resting spores can remain dormant of hundreds of years. We will analyse the communities of fungi that are found in the proximity of scientific stations and compare them with 'natural' communities in Antarctica, to determine what impact Man has had on introducing fungal species. The data generated will provide us with an insight into the colonisation of Antarctica by fungi. As global warming continues, species hitherto unable to establish may be able to do so. It is important to have a baseline on what is currently living on the continent, so that we can monitor the establishment of new species in the future.Thalli of the lichens Buellia frigida and Xanthoria elegans were collected from five different locations each 5-15 km apart in the Vestfold Hills, Princess Elizabeth Land, eastern Antarctica. A further collection was made from Mawson Station, Mac Robertson Land, eastern Antarctica 660 km away. DNA was extracted from whole thalli and the ribosomal ITS region amplified by PCR using fungal specific primers. Resulting products were sequenced to gain an indication of whether or not variation was present within populations of lichen-forming fungi from continental Antarctica, and therefore of the availability of genetic resources to react to pressures such as climate change. Three genotypes of B. frigida and two of X. elegans were detected in the Vestfold Hill collections. However, these differed by only one nucleotide position suggesting the presence of relatively little genetic variation if the ITS region is indicative of the overall genome. B. frigida collected from Mawson Station had an identical ITS region sequence to the most common Vestfold Hills genotype, indicating that this species may have a low level of genetic variation across much of eastern Antarctica. In contrast, X. elegans collected from Mawson showed considerable genetic variation from the Vestfolds thalli, differing at 14.2 % of nucleotide positions and had an identical ITS region sequence to an isolate from maritime Antarctica 4960 km away. Samples from the Vestfold Hills formed a distinct cluster in a phylogenetic analysis of ITS sequences from a worldwide collection of X. elegans isolates.The collection sites used in this study were:Lichen Valley, Vestfold HillsStalker Hill, Vestfold HillsEllis Rapids, Vestfold HillsTrajer Ridge, Vestfold HillsBoulder Hill, Vestfold HillsMawson Station.The DNA sequences arising from the lichens can be accessed from Genbanks Entrez Nucleotide Sequence Search, the accession numbers are:AF276066-AF276070AF281306-AF281307AF278753-AF278757This work was carried out as part of ASAC project 1201 (ASAC_1201).

南极洲是一片以微生物（micro-organisms）为优势类群的荒漠大陆。沿岸区域显眼的海豹与企鹅依赖海洋获取食物资源，实际上属于海洋食物链的组成部分。
生命活动依赖游离水的存在。在南极洲，水通常以冰的形式封存，仅在夏季，陆地环境中才会出现游离水。不仅水资源匮乏，低温与低营养水平也严重限制了成功定植于该大陆的微生物的生长潜力。
繁殖体（propagules）通过多种途径被携带至南极洲。部分繁殖体随环绕地球的气团抵达，沉降后无法适应极端环境而死亡，另有部分则可成功定植。另有部分微生物物种可通过人类活动被引入至大陆上的科学考察站周边区域。
在地质历史中反复出现的冰期内，微生物可依托冰原岛峰（nunataks）或冰层提供的避难所（refugia）存活，并在冰川退却后重新广泛定植于大陆各处。
本研究将聚焦于微生物类群中的真菌。我们将使用专用空气采样器，以确定哪些真菌物种随气流被携带至南极洲；同时会将这些采样器收集的繁殖体，与“土壤”中栖息的真菌物种以及从冰样本中培养得到的真菌物种（这类样本中的休眠孢子可休眠数百年）进行比对。我们还将分析科学考察站周边的真菌群落，并与南极洲的“天然”真菌群落进行比对，以确定人类活动在引入真菌物种方面造成的影响。
本研究产生的数据将帮助我们深入了解真菌对南极洲的定植过程。随着全球变暖持续推进，此前无法成功定植的物种或许能够实现定植。获取当前南极洲本土生物的基线数据至关重要，以便我们未来能够监测新物种的定植情况。
研究人员从东南极伊丽莎白公主地范达福斯丘陵的5处间距5~15公里的采样点，采集了冷布埃利亚地衣（Buellia frigida）与优雅黄枝衣（Xanthoria elegans）的地衣体（thallus，复数thalli）；另从660公里外的东南极麦克罗伯逊地的莫森站（Mawson Station）采集了额外样本。
研究人员从完整地衣体中提取DNA，并使用真菌特异性引物通过聚合酶链式反应（Polymerase Chain Reaction，PCR）扩增核糖体ITS区域（ribosomal ITS region）。对扩增产物进行测序，以探究南极大陆地衣型真菌（lichen-forming fungi）种群内是否存在遗传变异，进而明确其应对气候变化等压力的遗传资源储备情况。
在范达福斯丘陵的采样样本中，共检测到冷布埃利亚地衣的3种基因型以及优雅黄枝衣的2种基因型；但这些基因型仅存在1个核苷酸位点的差异，这表明若以ITS区域作为全基因组的参考指标，该类群的遗传变异水平相对较低。
从莫森站采集的冷布埃利亚地衣，其ITS区域序列与范达福斯丘陵最常见的基因型完全一致，这表明该物种在东南极大部分区域的遗传变异水平可能较低。
与之相反，从莫森站采集的优雅黄枝衣与范达福斯丘陵的地衣体存在显著遗传差异，在14.2%的核苷酸位点上存在变异；且其ITS区域序列与4960公里外的海洋性南极洲分离株完全一致。
在基于全球优雅黄枝衣分离株ITS序列的系统发育分析中，范达福斯丘陵的样本形成了一个独立的进化枝。
本研究使用的采样点如下：范达福斯丘陵的地衣谷（Lichen Valley）、范达福斯丘陵的斯托克山（Stalker Hill）、范达福斯丘陵的埃利斯急流（Ellis Rapids）、范达福斯丘陵的特拉杰岭（Trajer Ridge）、范达福斯丘陵的博尔德山（Boulder Hill）以及莫森站（Mawson Station）。
本研究涉及的地衣DNA序列可通过GenBank的Entrez核苷酸序列搜索（Entrez Nucleotide Sequence Search）获取，登录号为：AF276066~AF276070、AF281306~AF281307以及AF278753~AF278757。
本研究作为南极科学咨询委员会（Antarctic Science Advisory Committee，ASAC）项目1201（ASAC_1201）的一部分完成。