Naraki Yuka, Hiruta Chizue, Tochinai Shin
Department of Natural History Sciences, Hokkaido University, Kita-ku, Sapporo, Hokkaido, Japan.
Zoolog Sci. 2013 Aug;30(8):619-25. doi: 10.2108/zsj.30.619.
Many organisms have the ability to alter their development in the presence of predators, leading to predator-induced defenses that reduce vulnerability to predation. In the water flea Daphnia pulex, small protuberances called 'neckteeth' form in the dorsal neck region in response to kairomone(s) released by predatory phantom midges (Chaoborus larvae). Although previous studies suggested that kairomone sensitivity begins when chemoreceptors begin to function during embryogenesis, the exact critical period was unknown to date. In this study, we investigated the period of kairomone sensitivity and the process of necktooth formation in D. pulex through extensive treatments with pulses of kairomone(s). First, we described the time course of embryogenesis, which we suggest should be used as the standard in future studies. We found the kairomone-sensitive period to be relatively short, extending from embryonic stage 4 to postembryonic first instar. We observed cell proliferation and changes in cell structure in response to the kairomone treatment, and propose a model for necktooth formation. Preliminary LiCl treatment suggests the Wnt signaling pathway involved in crest formation as a candidate for the molecular mechanism underlying this process. Our study provides basic insight toward understanding the mechanisms underlying adaptive polyphenism in D. pulex.
许多生物在有捕食者存在的情况下能够改变自身发育，从而产生捕食者诱导防御，降低被捕食的易感性。在水蚤（大型溞）中，其颈部背侧区域会因捕食性幽蚊（幽蚊幼虫）释放的信息素而形成名为“颈齿”的小突起。尽管先前的研究表明，在胚胎发育过程中化学感受器开始发挥作用时，信息素敏感性就开始了，但迄今为止确切的关键时期尚不清楚。在本研究中，我们通过用信息素脉冲进行广泛处理，研究了大型溞对信息素的敏感时期以及颈齿形成过程。首先，我们描述了胚胎发育的时间进程，建议在未来研究中将其作为标准。我们发现信息素敏感时期相对较短，从胚胎第4阶段延伸至胚后第一龄期。我们观察到细胞增殖以及细胞结构因信息素处理而发生的变化，并提出了一个颈齿形成模型。初步的氯化锂处理表明，参与嵴形成的Wnt信号通路是这一过程潜在分子机制的候选者。我们的研究为理解大型溞适应性多型现象的潜在机制提供了基本见解。
