北京时间7月24日消息，日本科学家表示，蜗牛被鸟儿吞下肚后，能够完好无损地幸存下来。日本母岛上的暗绿绣眼鸟喜欢吃微小的陆地蜗牛。他们发现，15%的蜗牛经过鸟儿的消化道，并随粪便排出体外后仍然活着。
鸟儿排泄物里的小蜗牛能够幸存下来
蚤蜗牛是母岛上最常见的一种蜗牛
这些证据表明，鸟儿的捕食行为可能是蜗牛群体扩散到其他地方的一个关键因素。众所周知，鸟儿在吃掉水果的同时，会把植物种子带到别的地方。日本东北大学的研究人员想通过这项研究，看一看蜗牛等无脊椎动物是否也能通过上述方式扩散开来。该研究成果发表在《生物地理学》杂志上。
以前的研究显示，池塘里的蜗牛被鱼吞下肚后能够幸存下来，但是没人知道陆地蜗牛是否也存在类似情况。对在母岛上生活的鸟儿的饮食情况进行研究后，科学家确定暗绿绣眼鸟特别喜欢吃微小的陆地蜗牛——蚤蜗牛( Tornatellides boeningi )。他们在实验室里喂食暗绿绣眼鸟这种蜗牛吃，看一看一些小蜗牛是否能忍受住鸟儿的消化过程，最后幸存下来。
研究人员裕也一郎(Shinichiro Wada)解释说：“令我们感到吃惊的是，竟有大约15%的小蜗牛经过鸟儿的肠胃后，仍然活着。”他们还研究了在该岛不同地区发现的蚤蜗牛的遗传差异，发现它们发生了很大变化。研究人员发现，它们并非只与附近的蜗牛进行交配，这表明，虽然蜗牛存在地理隔离，但是不同群体间是有联系的。
裕也一郎说：“受到地域限制的无翼陆生无脊椎动物，尤其是蜗牛为什么能够迁移到很远的地方？也许通过以下解释可以揭开这个谜底：借助鸟儿的足、肠胃，亦或是龙卷风。这是第一项研究显示，蜗牛确实能通过鸟儿的消化系统后幸存下来，并被散布到更加广阔的区域。”
一只蜗牛帮助研究人员确定了大量蜗牛是如何借助鸟儿的粪便进行远距离迁徙的。裕也一郎说：“一只蜗牛在被鸟儿吞下肚后不久产下了大量小蜗牛。”据科学家说，蜗牛得以幸存下来的一个主要原因是它们的体型小。以前的研究发现，平均直径是2.5毫米的微型蜗牛比大个蜗牛更容易幸存下来，因为后者在被鸟儿吞下肚时，外壳已经严重受损。
裕也一郎和他的同事们称，他们将通过进一步的研究，弄明白这些幸存下来的蜗牛除了体型小以外，是否还具备其他特殊适应能力，才不会被鸟儿消化掉。母岛位于东京南部大约1000公里处，是日本小笠原群岛的组成部分。这座岛屿因其丰富的生态系统最近被联合国教科文组织列入《世界遗产名录》。(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.
