Denver R J
Department of Biology, The University of Michigan, Ann Arbor, Michigan, 48109-1048, USA.
Gen Comp Endocrinol. 1998 Jun;110(3):326-36. doi: 10.1006/gcen.1998.7082.
Tadpoles of several amphibian species have been shown to accelerate metamorphosis when their ponds dry. To understand the proximate mechanisms that mediate the developmental response to pond drying, I analyzed changes in endocrine activity in tadpoles of the Western spadefoot toad (Scaphiopus hammondii) exposed to experimental water volume reduction in the laboratory. Tadpoles exposed to a declining water level accelerated metamorphosis compared with tadpoles raised in a constant high water environment. The acceleration of development was associated with the precocious elevation of whole-body contents of the hormones that control metamorphosis, the thyroid hormones thyroxine (T4) and triidothyronine (T3), and the interrenal steroid corticosterone (CORT). The precocious activation of the thyroid system preceded external morphological change (i.e., increase in hind limb length, developmental stage) by 3 days. To test if tadpoles are capable of responding rapidly to water volume reduction, mid-prometamorphic tadpoles (Gosner Stage 37-38) were raised in a constant high water environment (10 L) and then transferred to either 1 or 10 L. Tadpoles transferred to 1 L exhibited significant metamorphic changes by 48 h after transfer. In addition, dramatic elevations in whole-body T4, T3, and CORT contents were evident at this time point. Thus, the metamorphic response to pond drying is likely driven by the activation of the thyroid and interrenal axes, the hormones of which control metamorphosis. Furthermore, this response is rapid, occurring within 48 h after exposure to the desiccating environment.
已有研究表明，几种两栖动物的蝌蚪在池塘干涸时会加速变态发育。为了解介导对池塘干涸发育反应的近端机制，我分析了在实验室中经历实验性水量减少的西部锄足蟾（Scaphiopus hammondii）蝌蚪的内分泌活动变化。与在恒定高水位环境中饲养的蝌蚪相比，暴露于水位下降环境中的蝌蚪加速了变态发育。发育加速与控制变态发育的激素——甲状腺激素甲状腺素（T4）和三碘甲状腺原氨酸（T3）以及肾上腺皮质类固醇皮质酮（CORT）的全身含量早熟升高有关。甲状腺系统的早熟激活比外部形态变化（即后肢长度增加、发育阶段）提前3天。为了测试蝌蚪是否能够对水量减少做出快速反应，将处于前变态中期的蝌蚪（戈斯纳37 - 38期）饲养在恒定高水位环境（10升）中，然后转移到1升或10升的环境中。转移到1升环境中的蝌蚪在转移后48小时内出现了明显的变态变化。此外，此时全身T4、T3和CORT含量显著升高。因此，对池塘干涸的变态反应可能是由甲状腺和肾上腺轴的激活驱动的，其激素控制着变态发育。此外，这种反应很快，在暴露于干燥环境后48小时内就会发生。
