BUTTERFLY EFFECT:  Genetic bar codes and ecological data revealed that the neotropical skipper butterfly Astraptes fulgerator is actually a complex of 10 species. Whether bar coding by itself can define species is controversial.

Bending to Bar Codes  Is a one-gene method to define species truly effective?

By Sara Beardsley

By the close of the 20th century, taxonomy had reached a crossroads. Funds were declining and academic interest dwindling, even as biologists and conservationists raced to identify and quantify species. "During my long engagement in the tropics, I've been confronted with the frustration that all biologists feel, with no knowledge of the life systems around them," explains evolutionary biologist Paul D. N. Hebert, who holds the Canada Research Chair in Molecular Biodiversity. So, in 2003, Hebert proposed a new ID system, sidestepping the cumbersome taxonomic legwork: "tag" species according to a segment of a mitochondrial gene. These so-called DNA bar codes instantly won public favor, heralding a day when researchers could run simple DNA tests in the field, perhaps even with a Star Trek-ian "tricorder" device. But since its advent, scores of taxonomists have decried the shortcut, claiming it will undermine the purposely elaborate systems developed to ensure ID precision and accuracy.
Hebert's scheme focuses on a sequence fragment from the cytochrome c oxidase I (COI) gene, which he claims is unique to separate taxa. He and his colleagues demonstrated proof of principle last year, when DNA bar codes correctly predicted independent species in groups of previously undistinguished birds and butterflies. In a February meeting in London, the Consortium for the Barcode of Life announced plans to bar-code all birds and fish within the next five years, as well as identify all flowering plants in Costa Rica. The initiatives are stepping-stones on the way to their much grander goal: a gene tag for every living thing and a catalogue of the earth's biodiversity (only about one tenth of the world's species are formally known).
 
But like anything, warns entomologist Quentin D. Wheeler of the Natural History Museum in London, bar coding "can be used for good or evil." A standardized species marker is exciting, provided it corresponds to formal descriptions and classifications. To Wheeler and other critics, it is bar coders' more ambitious goal--applying the COI system backward to create "provisional" new-species definitions--that threatens to hamper taxonomic progress.

The problem, naysayers argue, is oversimplification. "Nature is messy," points out entomologist Daniel Rubinoff of the University of Hawaii at Manoa. Multiple species definitions exist today because nobody knows what qualifies as speciation; the very "science" of taxonomy involves analyzing hundreds of characters to make these distinctions--which is why the one-character data sets used by bar coders "are like returning to the Dark Ages," Rubinoff says. Biologist Brent D. Mishler of the University of California at Berkeley concurs, calling bar coding for species identification "extremely wrongheaded and damaging to the fabric of systematics," which currently relies on extensive morphological, ecological and genetic data to frame species in an evolutionary context.
Critics also raise eyebrows over bar coding's accuracy. Hebert pegs the error rate at 2 percent, small enough to validate the approach for animals. But so far only a few proofs of principle have emerged, and the tests have been easy. "Close sister species are usually the most important to identify correctly," says biologist Felix Sperling of the University of Alberta. And those are the ones scientists may have the greatest trouble resolving through COI. Recently split taxa or cases of hybridization, where independent species have produced offspring, pose particular challenges because sequences may not have evolved to reflect those events yet.

Hebert argues that the system is meant to augment current taxonomy by "heaping life into piles" that can later be revised. But with a price tag between $1 billion and $2 billion, critics worry that the initiative will only divert funds and leave "real" taxonomy to clean up the mess. "In the age of cyber-infrastructure, digital tools, and IT," Wheeler and others write in a paper in press for the journal Systematic Biology, "most of the weights that have held taxonomy back are gone. [But] now ... it is in danger of being tossed out like rubbish for the latest parlor trick."

Experts also point out that bar codes cannot be integrated with the other major systematics enterprise--the Tree of Life, a peer-reviewed cladogram linking all known phylogenetic relationships. (Bar codes provide too little evidence to justify formal species designations on it.) At best, Hebert's database will e xist alongside the tree, superimposing untested "leaves." Hebert claims that despite the obstacles "we're finally tapping into an automated, digital information stream," but others note that cut-and-dry codes seem to overlook the essential meaning of species: ever changing end points in the hands of evolution.

    據(jù)Sciam網(wǎng)5月9日?qǐng)?bào)道,，隨著二十世紀(jì)的結(jié)束,，生物分類(lèi)學(xué)也走到了十字路口。盡管生物學(xué)家和自然資源保護(hù)學(xué)家爭(zhēng)相尋找和鑒別新的物種，但是全世界投入到生物分類(lèi)學(xué)的資金仍然日益減少,，分類(lèi)學(xué)的學(xué)術(shù)價(jià)值也在不斷下降,。

    加拿大生物多樣化研究帶頭人,、生物學(xué)家Paul·Hebert說(shuō)道,，他在熱帶雨林生活了很長(zhǎng)一段時(shí)間，遇到過(guò)許多和其他生物學(xué)家一樣的問(wèn)題,，熱帶雨林中的生物種類(lèi)實(shí)在太多了,，到目前為止人們對(duì)它們還是知之甚少。所以Hebert于2003年提出一種新的生物物種標(biāo)識(shí)體系,，借此改變現(xiàn)有分類(lèi)學(xué)煩雜的分類(lèi)方法,。這種分類(lèi)方法通過(guò)分析生物自身遺傳的線(xiàn)粒體DNA中的某一部分 ，就可以準(zhǔn)確的判斷出這種生物是屬于什么種類(lèi),。這種分類(lèi)方法很快受到了生物學(xué)家們的歡迎與認(rèn)可,，因?yàn)槔煤?jiǎn)單的分析儀器，生物學(xué)家就可以在熱帶雨林中進(jìn)行實(shí)地生物分類(lèi),。但是這種分類(lèi)方法的使用也遭到了許多分類(lèi)學(xué)者的詆毀,，他們認(rèn)為這種分類(lèi)方法嚴(yán)重破壞了現(xiàn)有精細(xì)的分類(lèi)體系，使得分類(lèi)的準(zhǔn)確度大大降低,。

    Hebert的基因檢測(cè)分類(lèi)方法主要通過(guò)分析細(xì)胞色素C氧化酶中的一段基因序列碎片來(lái)測(cè)定生物的種類(lèi),，這段序列碎片可以準(zhǔn)確標(biāo)識(shí)出不同生物種類(lèi)間的差別。他和同事于2004年證實(shí)了此項(xiàng)分類(lèi)方法的正確性,。他們運(yùn)用此方法準(zhǔn)確地發(fā)現(xiàn)了新的鳥(niǎo)類(lèi)和蝴蝶物種,。之前這些物種都被混雜在其它已有的物種中,，沒(méi)有被生物學(xué)家鑒別出來(lái),。 生物科學(xué)家們于2005年2月份在倫敦討論后宣布，在未來(lái)的五年里,，生物學(xué)家將對(duì)所有的鳥(niǎo)類(lèi),、魚(yú)類(lèi)和有花植物進(jìn)行基因分類(lèi)。此項(xiàng)舉動(dòng)是生物分類(lèi)學(xué)領(lǐng)域通往新的輝煌的一塊基石,。目前世界上只有大約十分之一的物種為人們所認(rèn)識(shí)和分類(lèi),，生物分類(lèi)學(xué)的最終目標(biāo)是把地球上存在的所有物種進(jìn)行系統(tǒng)而準(zhǔn)確的分類(lèi)。