對葉子化石的一項新研究表明,，5000多萬年前,，全球突然變暖期間，昆蟲蜂擁而至,，進犯了今日美國北部的一些地區(qū),。該研究成果發(fā)表在不久前出版的美國《國家科學院院刊》（PNAS）上。研究指出,，在我們現(xiàn)階段的氣候變暖過程中也可能會發(fā)生同樣的情況,。
一個地區(qū)的昆蟲是否具有多樣性，可以通過當?shù)刂参锶~子遭受破壞的程度和類型推斷出來,。據(jù)該研究的發(fā)起人,、賓夕法尼亞州立大學的研究生艾倫·柯拉諾介紹，大口咀嚼的昆蟲在葉子上留下的疤痕不同,，這可以在化石中看到,。
研究人員發(fā)現(xiàn)，熱帶地區(qū)的昆蟲種類最豐富,，對植物葉子所造成的破壞也最多,。這表明，較高的氣溫跟昆蟲的多樣性之間是相互關(guān)聯(lián)的,。
研究人員在來自懷俄明州畢葛紅盆地（BighornBasin）的5000多塊葉子化石中尋找疤痕證據(jù),。這些化石可以追溯到古新世-始新世極熱時期(PETM)及其前后。古新世-始新世極熱是大約5600萬年前發(fā)生的一次全球突然變暖事件,，跟目前的氣候變化狀況具有可比性,。食葉昆蟲留下痕跡的多少、類型以及吞掉葉子的比例,，能夠說明這個地區(qū)在不同的氣候條件下爬行昆蟲的多少,。
研究人員發(fā)現(xiàn)，古新世末期較為涼爽,，15%至38%的葉子遭受了昆蟲的毀壞,；在始新世初始階段,、極熱時期過后氣溫有所下降時,，33%的葉子遭到破壞,；而在極熱時期，有57%的葉子遭到破壞,?？梢钥吹剑瑯O熱時期葉子遭到各種破壞的比例有了明顯的上升,。
柯拉諾及同事認為,，這些昆蟲的胃口變大是由于古新世-始新世極熱時期二氧化碳水平上升造成的，這使得植物葉子的營養(yǎng)成分減少,?？吕Z解釋說：“如果植物可以利用的二氧化碳較多，光合作用就會變得更加容易,，植物無需在葉子中儲存大量的蛋白質(zhì)而同樣能夠提供自身所需的營養(yǎng),。因此，跟以前相比,，昆蟲必須吃掉更多的葉子才能得到同樣多的營養(yǎng),。”
研究小組研究的三個不同時段的植物各不相同。在古新世-始新世極熱時期,，植物的多樣性有所增加,，這表明隨著氣溫升高，植物品種逐漸地從墨西哥灣沿岸地區(qū)遷移出去,?？吕Z認為昆蟲的遷移可能沿著相同的路線進行——“昆蟲跟隨著它們在遙遠的南方食用的植物遷移過來的。”
在范圍大小和變暖速度上,，古新世-始新世極熱時期跟目前的氣候變化都具有可比性,。因此，柯拉諾及同事認為,，饑餓昆蟲進犯的事件很可能發(fā)生于當今時代,。
生物谷推薦原始出處：
PNAS 2008 105: 3815-3818; published online on March 3, 2008, 10.1073/pnas.0710180105
The oldest North American primate and mammalian biogeography during the Paleocene–Eocene Thermal Maximum
K. Christopher Beard
Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, PA 15213
Edited by Alan Walker, Pennsylvania State University, University Park, PA, and approved January 10, 2008 (received for review October 25, 2007)
Undoubted primates first appear almost synchronously in the fossil records of Asia, Europe, and North America. This temporal pattern has complicated efforts to reconstruct the early dispersal history of primates in relation to global climate change and eustatic fluctuations in sea level. Here, I describe fossils from the Tuscahoma Formation on the Gulf Coastal Plain of Mississippi documenting an anatomically primitive species of Teilhardina that is older than other North American and European primates. Consistent with its antiquity, a phylogenetic analysis of dental characters recognizes Teilhardina magnoliana, sp. nov., as the most basal member of this genus currently known from either North America or Europe. Its stratigraphic provenance demonstrates that primates originally colonized North America near the base of the Paleocene–Eocene Thermal Maximum (PETM), but before an important fall in eustatic sea level. Correlation based on carbon isotope stratigraphy and sequence stratigraphy indicates that the earliest North American primates inhabited coastal regions of the continent for thousands of years before they were able to colonize the Rocky Mountain Interior. The transient provincialism displayed by early North American primates corresponds to similar biogeographic patterns noted among fossil plants. Decreased precipitation in the Rocky Mountain Interior during the early part of the PETM may have been an important factor in maintaining biotic provincialism within North America at this time. These results underscore the need to obtain multiple, geographically dispersed records bearing on significant macroevolutionary events such as the PETM.
