Guidetti Roberto, Boschini Deborah, Altiero Tiziana, Bertolani Roberto, Rebecchi Lorena
Department of the Museum of Paleobiology and Botanical Garden, Via Università 4, 41100, Modena, Italy.
J Exp Biol. 2008 Jul;211(Pt 14):2296-302. doi: 10.1242/jeb.015131.
Stressful environmental conditions limit survival, growth and reproduction, or these conditions induce resting stages indicated as dormancy. Tardigrades represent one of the few animal phyla able to perform both forms of dormancy: quiescence and diapause. Different forms of cryptobiosis (quiescence) are widespread and well studied, while little attention has been devoted to the adaptive meaning of encystment (diapause). Our goal was to determine the environmental factors and token stimuli involved in the encystment process of tardigrades. The eutardigrade Amphibolus volubilis, a species able to produce two types of cyst (type 1 and type 2), was considered. Laboratory experiments and long-term studies on cyst dynamics of a natural population were conducted. Laboratory experiments demonstrated that active tardigrades collected in April produced mainly type 2 cysts, whereas animals collected in November produced mainly type 1 cysts, indicating that the different responses are functions of the physiological state at the time they were collected. The dynamics of the two types of cyst show opposite seasonal trends: type 2 cysts are present only during the warm season and type 1 cysts are present during the cold season. Temperature represents the environmental factor involved in induction, maintenance and termination of the cyst. We also obtained evidence that A. volubilis is able to perform both diapause and cryptobiosis, even overlapping the two phenomena. The induction phase of tardigrade encystment can be compared to the induction phase of insect diapause, also indicating an involvement of endogenous factors in tardigrade encystment. As in insect diapause, tardigrade encystment can be considered a diapausing state controlled by exogenous and endogenous stimuli.
恶劣的环境条件会限制生存、生长和繁殖，或者这些条件会诱导出以休眠表示的静止阶段。缓步动物是少数能够进行两种休眠形式的动物门类之一：静止和滞育。不同形式的隐生现象（静止）广泛存在且研究充分，而对于包囊化（滞育）的适应性意义却很少有人关注。我们的目标是确定参与缓步动物包囊化过程的环境因素和信号刺激。我们研究的是真缓步纲的缠绕双节缓步虫，这是一种能够产生两种类型包囊（1型和2型）的物种。我们进行了实验室实验以及对一个自然种群的包囊动态进行了长期研究。实验室实验表明，4月采集的活跃缓步动物主要产生2型包囊，而11月采集的动物主要产生1型包囊，这表明不同的反应是它们采集时生理状态的函数。两种类型包囊的动态呈现相反的季节性趋势：2型包囊仅在温暖季节出现，1型包囊在寒冷季节出现。温度是参与包囊诱导、维持和终止的环境因素。我们还获得了证据表明缠绕双节缓步虫能够进行滞育和隐生，甚至这两种现象会重叠。缓步动物包囊化的诱导阶段可以与昆虫滞育的诱导阶段相比较，这也表明内源性因素参与了缓步动物的包囊化过程。与昆虫滞育一样，缓步动物的包囊化可以被认为是一种由外源性和内源性刺激控制的滞育状态。
