Science：凤蝶幼虫变色之谜

生物谷报道：凤蝶的幼虫经过几次蜕皮后，颜色会突然从黑白变为鲜艳的绿色。日本科学家发现，幼虫体内保幼激素量的变化改变了基因的作用方式，从而促使幼虫变色。

凤蝶幼虫起先身披黑白相间斑纹，全身遍布瘤一样的凸起，它们以此伪装成鸟类的粪便，躲避天敌。而幼虫第四次蜕皮后，却变成可以融入周围草木的鲜艳的绿色，身上的凸起也消失了，因为它们长大一些后如果依然是鸟类粪便的样子，反而比较显眼。这个过程中，促使幼虫变色的机制以前一直没有得到解释。

日本东京大学教授藤原晴彦等人在新一期美国《科学》杂志上报告说，他们发现保幼激素与此相关。研究人员测量了幼虫体内的激素水平，发现保幼激素在幼虫体内的浓度在第三次蜕皮后的约１天内直线下降，这种变化导致幼虫第四次蜕皮后变色。而如果在刚完成第三次蜕皮的幼虫身上涂抹保幼激素，那么这些幼虫第四次蜕皮之后其身体斑纹依然是黑白相间。研究人员因此认为，保幼激素的浓度是凤蝶幼虫变色的关键。

保幼激素是昆虫在发育过程中分泌的一种激素，能抑制成虫特征出现，使幼虫蜕皮后仍保持幼虫状态。（新华网）

生物谷推荐英文原文：

Science 22 February 2008:
Vol. 319. no. 5866, p. 1061
DOI: 10.1126/science.1149786

Juvenile Hormone Regulates Butterfly Larval Pattern Switches

Ryo Futahashi1,2 and Haruhiko Fujiwara1*

Insect color patterns can be very diverse. This variation is also seen among many larval instar stages, which can take on vastly different phenotypes. Young caterpillars of the swallowtail butterfly, Papilio xuthus, are mimics of bird droppings, whereas the fifth larval instar is camouflaged among the leaves of host plants (cryptic pattern). We find that juvenile hormone (JH) titers decrease during the fourth larval instar. Furthermore, treatment with JH analog at the beginning of the fourth instar stage resulted in reproducing the mimetic pattern instead of the usual cryptic one and likewise altered gene expression patterns to that associated with the mimetic pattern. These findings suggest that JH regulates the progressive larval pattern switch of this insect.

1 Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience Building 501, Kashiwa, Chiba 277-8562, Japan.
2 National Institute of Agrobiological Sciences, 1-2 Owashi, Tsukuba, Ibaraki 305-8634, Japan.

* To whom correspondence should be addressed. E-mail: haruh@k.u-tokyo.ac.jp