北京時(shí)間7月24日消息,，日本科學(xué)家表示，蝸牛被鳥兒吞下肚后,，能夠完好無損地幸存下來。日本母島上的暗綠繡眼鳥喜歡吃微小的陸地蝸牛,。他們發(fā)現(xiàn)，15%的蝸牛經(jīng)過鳥兒的消化道,，并隨糞便排出體外后仍然活著,。
鳥兒排泄物里的小蝸牛能夠幸存下來
蚤蝸牛是母島上最常見的一種蝸牛
這些證據(jù)表明,，鳥兒的捕食行為可能是蝸牛群體擴(kuò)散到其他地方的一個(gè)關(guān)鍵因素。眾所周知,，鳥兒在吃掉水果的同時(shí)，會(huì)把植物種子帶到別的地方,。日本東北大學(xué)的研究人員想通過這項(xiàng)研究，看一看蝸牛等無脊椎動(dòng)物是否也能通過上述方式擴(kuò)散開來,。該研究成果發(fā)表在《生物地理學(xué)》雜志上,。
以前的研究顯示,，池塘里的蝸牛被魚吞下肚后能夠幸存下來，但是沒人知道陸地蝸牛是否也存在類似情況,。對(duì)在母島上生活的鳥兒的飲食情況進(jìn)行研究后,，科學(xué)家確定暗綠繡眼鳥特別喜歡吃微小的陸地蝸牛——蚤蝸牛( Tornatellides boeningi )。他們?cè)趯?shí)驗(yàn)室里喂食暗綠繡眼鳥這種蝸牛吃,，看一看一些小蝸牛是否能忍受住鳥兒的消化過程，最后幸存下來,。
研究人員裕也一郎(Shinichiro Wada)解釋說：“令我們感到吃驚的是，竟有大約15%的小蝸牛經(jīng)過鳥兒的腸胃后,，仍然活著。”他們還研究了在該島不同地區(qū)發(fā)現(xiàn)的蚤蝸牛的遺傳差異,，發(fā)現(xiàn)它們發(fā)生了很大變化,。研究人員發(fā)現(xiàn),，它們并非只與附近的蝸牛進(jìn)行交配，這表明,，雖然蝸牛存在地理隔離，但是不同群體間是有聯(lián)系的,。
裕也一郎說：“受到地域限制的無翼陸生無脊椎動(dòng)物,，尤其是蝸牛為什么能夠遷移到很遠(yuǎn)的地方？也許通過以下解釋可以揭開這個(gè)謎底：借助鳥兒的足,、腸胃，亦或是龍卷風(fēng),。這是第一項(xiàng)研究顯示,，蝸牛確實(shí)能通過鳥兒的消化系統(tǒng)后幸存下來，并被散布到更加廣闊的區(qū)域,。”
一只蝸牛幫助研究人員確定了大量蝸牛是如何借助鳥兒的糞便進(jìn)行遠(yuǎn)距離遷徙的,。裕也一郎說：“一只蝸牛在被鳥兒吞下肚后不久產(chǎn)下了大量小蝸牛,。”據(jù)科學(xué)家說，蝸牛得以幸存下來的一個(gè)主要原因是它們的體型小,。以前的研究發(fā)現(xiàn),，平均直徑是2.5毫米的微型蝸牛比大個(gè)蝸牛更容易幸存下來，因?yàn)楹笳咴诒圾B兒吞下肚時(shí),，外殼已經(jīng)嚴(yán)重受損。
裕也一郎和他的同事們稱,，他們將通過進(jìn)一步的研究,，弄明白這些幸存下來的蝸牛除了體型小以外,，是否還具備其他特殊適應(yīng)能力，才不會(huì)被鳥兒消化掉,。母島位于東京南部大約1000公里處,，是日本小笠原群島的組成部分。這座島嶼因其豐富的生態(tài)系統(tǒng)最近被聯(lián)合國教科文組織列入《世界遺產(chǎn)名錄》,。(生物谷 Bioon.com)
doi: 10.1111/j.1365-2699.2011.02559.x
PMC:3006442
PMID:16153702
Snails can survive passage through a bird’s digestive system
Shinichiro Wada, Kazuto Kawakami, Satoshi Chiba
Aim Predation is generally viewed as a factor that limits the distribution of animal prey species. However, in certain instances, such as seed dispersal, predation may enhance the dispersal capability of prey species. In a prior study, we found that land snails are preyed upon by the Japanese white-eye (Zosterops japonicus) and the brown-eared bulbul (Hypsipetes amaurotis) in the Ogasawara Islands. In this paper we provide experimental and field evidence indicating that land snails could potentially be dispersed through bird predation.
Location Hahajima Island of the Ogasawara Islands in the western Pacific.
Methods Experimentation was first performed to test whether the land snail Tornatellides boeningi could remain alive after being swallowed and passed through the bird digestive system. Next, in order to investigate the potential role of internal bird transport and dispersal of this snail, we investigated the relationship between the distribution of population genetic diversity in the snail and the regional geographical abundance of predatory birds. The population genetic structure of T. boeningi and isolation by distance were inferred with Arlequin. The association between nucleotide diversity in T. boeningi populations and population density of predators was examined using a generalized linear mixed model. We conducted a likelihood ratio test for the full model and for another model that removed the fixed effect.
Results Of the 119 snails fed to Japanese white-eyes and 55 snails fed to brown-eared bulbuls, 14.3% and 16.4% of the snails, respectively, passed through the gut alive. Additionally, one snail gave birth to juveniles after emerging from a bird’s gut. Significant heterogeneity among the populations of T. boeningi on Hahajima was indicated using AMOVA; however, there was no evidence of isolation by distance. A positive correlation was found between levels of mitochondrial DNA variation among and within T. boeningi populations and the density of Japanese white-eyes in the wild.
Main conclusions Bird predation appears to be a method of dispersal for T. boeningi, and our results suggest that bird-mediated dispersal plays a role in land snail population structure.
