Gomez-Mestre I, Tejedo M, Ramayo E, Estepa J
Departamento de Biología Evolutiva, Estación Biológica de Doñana, CSIC, Avda. Maria Luisa s/n, Pabellón de Perú, 41013 Sevilla, Spain.
Physiol Biochem Zool. 2004 Mar-Apr;77(2):267-74. doi: 10.1086/378143.
Water salinity represents an environmental stress for many species. Amphibians are particularly sensitive because they are generally poor osmoregulators, and most species are completely absent from brackish and saline environments. We experimentally examined the effect of different salinity levels on larvae of the toad Bufo calamita L., a species that occupies freshwater ponds but can also breed in brackish ponds. Two independent experiments are reported here. In both experiments, tadpoles under saline conditions (ranging between 85 and 200 mOsm) showed a slower developmental rate, metamorphosing between 4 and 9 d later than the controls. Bufo calamita tadpoles reared in brackish water increased their osmolality and solute concentration (mainly sodium and chloride), decreased their levels of glucose, and decreased the total protein content, all measured from whole-animal extracts. Although most larval anurans are strictly ammoniotelic until the completion of metamorphosis, a few species exposed to dehydrating environments have evolved the ability to use urea as an osmolyte during the larval phase. The data presented here reveal that although B. calamita seems to be yet another exception to the rule of larval strict ammoniotelism, the tadpoles are not able to use urea as an osmolyte and rely on sodium-chloride balance instead. Preliminary immunoassays of thyroid hormone content suggest a possible decrease in hormone levels induced in water salinity conditions that correlate with a decreased developmental rate.
水体盐度对许多物种而言是一种环境压力。两栖动物尤其敏感，因为它们通常是较差的渗透压调节者，而且大多数物种完全不存在于半咸水和咸水环境中。我们通过实验研究了不同盐度水平对蟾蜍（Bufo calamita L.）幼体的影响，该物种栖息于淡水池塘，但也能在半咸水池塘中繁殖。本文报道了两项独立实验。在这两项实验中，处于盐度条件下（范围在85至200毫渗量）的蝌蚪发育速度较慢，变态时间比对照组晚4至9天。在半咸水中饲养的Bufo calamita蝌蚪提高了其渗透压和溶质浓度（主要是钠和氯），降低了葡萄糖水平，并降低了总蛋白含量，所有这些都是从全动物提取物中测得的。尽管大多数蛙类幼体在变态完成之前严格以氨为含氮排泄物，但一些暴露于脱水环境的物种已经进化出在幼体阶段将尿素用作渗透溶质的能力。此处呈现的数据表明，尽管Bufo calamita似乎是幼体严格氨排泄规则的又一个例外，但蝌蚪无法将尿素用作渗透溶质，而是依赖氯化钠平衡。甲状腺激素含量的初步免疫测定表明，在与发育速度降低相关的水体盐度条件下，激素水平可能会下降。
