美國研究人員最近發(fā)現(xiàn)，從上個冰川時代殘留下來的阿德利企鵝骨骼中提取的DNA樣本將有助于揭示物種如何應(yīng)對氣候變化,。
布里斯班市格里菲斯大學(xué)的進(jìn)化生物學(xué)家David Lambert在新一期遺傳學(xué)雜志《公共科學(xué)圖書館·遺傳學(xué)》（PLoS Genetics）上發(fā)表了他們對于生活在3.7萬前的企鵝DNA樣本的分析成果。Lambert教授說,，對于研究氣候變化,，企鵝是非常合適的物種,。它們在生活環(huán)境中感受的溫度變化要比赤道地區(qū)的那些動物劇烈的多。
自從上一次盛冰期以來,，企鵝們已經(jīng)經(jīng)歷了地球上多次出現(xiàn)的氣候變暖,。他估計在距今十二萬年的上個冰期之前，企鵝們就已經(jīng)存在了,。
阿德利企鵝在相當(dāng)長的時期中都保持了相當(dāng)大的種群數(shù)量,，這樣的物種并不多見。一個物種通?？梢酝ㄟ^地理上的遷徙讓自己生活在最適宜的溫度中,，從而應(yīng)對氣候變化帶來的影響。但是阿德利企鵝從沒有遷移到別處,，它們一直都呆在最冷的地方,。
阿德利企鵝能在劇烈的溫度變化中生存下來，說明有些物種能夠在不遷徙的情況下應(yīng)對氣候變化帶來的考驗,。Lambert和同事們對南極洲企鵝進(jìn)化速率的研究或許可以揭開這個現(xiàn)象背后的秘密,。
研究人員從在南極極端干燥和寒冷的環(huán)境中保存下來的三萬七千年前的企鵝骨骼中提取了多份DNA樣本。他們將現(xiàn)在在南極生活的企鵝媽媽和他們孩子的基因樣本進(jìn)行比對,，并再和它們祖先的DNA進(jìn)行比對,。結(jié)果顯示，三萬七千年來企鵝代際變化速率一直保持穩(wěn)定,。
這一發(fā)現(xiàn)反擊了當(dāng)前生物學(xué)者對進(jìn)化速率的一種認(rèn)識,，他們認(rèn)為生物進(jìn)化在短期會加快，而長期則相對較慢,。更為重要的成果是,，Lambert和他的團隊發(fā)現(xiàn)驗證了早期的研究成果，阿德利企鵝的進(jìn)化速率比現(xiàn)在人們想象的要快,。這也可能解釋為什么這些企鵝能夠在氣候劇烈變化的環(huán)境中存活下來,。進(jìn)化速率和企鵝一樣快的動物還有一種新西蘭特有的爬行動物tuatoara、野牛,、棕熊和穴居獅子等,。
這些DNA分析將焦點放在基因變化而不是自然選擇。所謂“中性”基因?qū)τ谛纬梢粋€演變速率穩(wěn)定的“生物原子時鐘”至關(guān)重要,。而自然選擇造成的結(jié)果是生物演化在一些一段時間內(nèi)極為迅速,，而在其它時期則幾乎穩(wěn)定不動。阿德萊德大學(xué)的進(jìn)化生物學(xué)家Jeremy Austin認(rèn)為這項成果將促使人們質(zhì)疑進(jìn)化演變速率對時間的依賴性,。但是要揭示進(jìn)化速率快慢的話,，三萬七千年這個周期顯然還不夠長。生物學(xué)界討論進(jìn)化速率時,，通常會講到一百萬年甚至更長周期內(nèi)的變化,。將企鵝和更古老物種的DNA序列進(jìn)行對比可能更有說服力一些,。
Lambert相信他的團隊肯定會在南極大陸更深處的永久凍土層中發(fā)現(xiàn)百萬年前的企鵝遺跡。（生物谷Bioon.com）
生物谷推薦原始出處：
PLoS Genetics,，4(10): e1000209. doi:10.1371/journal.pgen.1000209,，Craig D. Millar, David M. Lambert
Mutation and Evolutionary Rates in Adélie Penguins from the Antarctic
Craig D. Millar1, Andrew Dodd2, Jennifer Anderson2, Gillian C. Gibb2, Peter A. Ritchie2¤a, Carlo Baroni3,4, Michael D. Woodhams5, Michael D. Hendy5, David M. Lambert2¤b*
1 Allan Wilson Centre for Molecular Ecology and Evolution, School of Biological Sciences, University of Auckland, Auckland, New Zealand, 2 Allan Wilson Centre for Molecular Ecology and Evolution, Institute of Molecular BioSciences, Massey University, Auckland, New Zealand, 3Dipartmento Scienze della Terra, Università di Pisa, Pisa, Italy, 4 Consiglio Nazionale Ricerche, Centro Studio Geologia Strutturale, Pisa, Italy, 5 Allan Wilson Centre for Molecular Ecology and Evolution, Institute of Fundamental Sciences, Massey University Palmerston North, Palmerston North, New Zealand
Precise estimations of molecular rates are fundamental to our understanding of the processes of evolution. In principle, mutation and evolutionary rates for neutral regions of the same species are expected to be equal. However, a number of recent studies have shown that mutation rates estimated from pedigree material are much faster than evolutionary rates measured over longer time periods. To resolve this apparent contradiction, we have examined the hypervariable region (HVR I) of the mitochondrial genome using families of Adélie penguins (Pygoscelis adeliae) from the Antarctic. We sequenced 344 bps of the HVR I from penguins comprising 508 families with 915 chicks, together with both their parents. All of the 62 germline heteroplasmies that we detected in mothers were also detected in their offspring, consistent with maternal inheritance. These data give an estimated mutation rate (μ) of 0.55 mutations/site/Myrs (HPD 95% confidence interval of 0.29–0.88 mutations/site/Myrs) after accounting for the persistence of these heteroplasmies and the sensitivity of current detection methods. In comparison, the rate of evolution (k) of the same HVR I region, determined using DNA sequences from 162 known age sub-fossil bones spanning a 37,000-year period, was 0.86 substitutions/site/Myrs (HPD 95% confidence interval of 0.53 and 1.17). Importantly, the latter rate is not statistically different from our estimate of the mutation rate. These results are in contrast to the view that molecular rates are time dependent.
