We investigated for the first time, the seasonal patterns of iono- and osmotic responses of the Souss Valley tortoises, , in an arid steppe-land of west-central Morocco, a year-round (2011–2012). The mean body mass condition index varied significantly over time, with significantly higher values in males in summer and autumn 2011. All the plasma variables (osmolality and sodium, potassium, chloride, and urea concentrations) varied significantly among seasons, increasing during the summer dry period and decreasing after rainstorms. Osmolality and solute concentrations in voided urine were more variable than in plasma, with more pronounced decreases related to rainfall events. Soluble potassium was the major cation in voided urine. Potassium concentration decreased markedly following rainfall events, and rapidly increased in late summer and autumn 2011, when some green plants were available. As spring progressed and tortoises gained body mass while feeding on hydrated vegetation, urine osmolalities decreased, and then re-increased during the dry summer period, becoming essentially iso-osmotic with plasma. When summer thundershowers dropped rain, tortoises drank water, voided concentrated bladder urine, and stored dilute urine; body mass, plasma and urine concentrations returned to hydrated levels. Tortoises exhibited a tolerance to osmotic stressors that allowed them to osmoregulate opportunistically in their arid environments via allostasis, a process that allows maintaining homeostasis through change. When bladder urine becomes iso-osmotic to plasma, tortoises tolerate increases in osmolality and concentrations of plasma solutes. The success of facultative osmoregulation and variable ‘allostasis’ would depend on the occurrence of summer rain events as a source of drinking in osmotically stressed tortoises.

中文翻译：

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摩洛哥中西部干旱草原上的苏斯谷陆龟 Testudo graeca graeca 对渗透应激源季节变化的适应：动态平衡与稳态

我们首次调查了摩洛哥中西部干旱草原上苏斯河谷陆龟全年（2011-2012）离子和渗透反应的季节模式。平均体重状况指数随时间变化显着，2011 年夏季和秋季男性的值显着较高。所有血浆变量（渗透压以及钠、钾、氯和尿素浓度）随季节变化显着，在夏季干燥期间增加期间，暴雨后逐渐减少。排泄尿液中的渗透压和溶质浓度比血浆中的变化更大，与降雨事件相关的下降更明显。可溶性钾是排尿中的主要阳离子。降雨事件后，钾浓度显着下降，并在 2011 年夏末和秋季迅速上升，此时出现了一些绿色植物。随着春天的到来，陆龟在吃水合植物的同时体重增加，尿液渗透压下降，然后在干燥的夏季期间重新增加，与血浆基本等渗。当夏季雷阵雨下雨时，乌龟会喝水，排出浓缩的膀胱尿，并储存稀释的尿液；体重、血浆和尿液浓度恢复到水合水平。陆龟表现出对渗透压应激源的耐受性，这使它们能够在干旱环境中通过动态平衡进行渗透调节，这一过程允许通过变化来维持体内平衡。当膀胱尿液与血浆等渗时，陆龟可以忍受血浆渗透压和血浆溶质浓度的增加。兼性渗透调节和可变“平衡”的成功取决于夏季降雨事件的发生，作为渗透应激陆龟的饮水来源。