Kidney functional morphology variations between spring and winter in the Saharan male lizard Uromastyx acanthinura (Sauria, Agamidae), with special reference to body water economy.

To better understand the adaptive mechanisms in Uromastyx acanthinura to the seasonal variations in the arid environment, the present study aimed to explore the kidney functional morphology involved in body water economy. These investigations were carried out by the histological, histochemical and immuno-histochemical methods using conventional light microscopy. The glomeruli number is estimated at 2000 per kidney. The glomeruli size is rather small and decreases significantly in winter. Interestingly, the proximal convoluted tubule (PCT) is long and divided into two different segments which is one of the particularities of this species. Both of the distal convoluted tubule (DCT), connecting tubule (CnT) and collecting duct (CD) epithelium contains mucous cells. The nature and intensity of these mucous secretions vary according to seasons. The evident hypertrophy of the secondary collecting duct (SCD) and tertiary collecting duct (TCD) epithelium is related to the high secretory activity during spring, corresponding to the sexual segment of kidney (SSK). Labeling with anti α-smooth muscle actin-1 showed a thick layer of mucularis surrounded the entire CD. Also, the mesangium of glomeruli contains myofibroblasts. All these renal structural characteristics involved in body water economy may be considered as an adaptive mechanisms of U. acanthinura to resist to dehydration and cope with seasonal variations in the arid environment.