Seasonal flexibility of kidney structure and factors regulating water and salt in Eremias multiocellata.

Although sodium and water reabsorption by the kidney plays a major role in maintaining body fluid homeostasis, the seasonal response of renal morphology and the factors involved in water and salt regulation are not well known, especially in reptiles. Eremias multiocellata is a typical desert-dwelling lizard. Here, we compared water and salt regulation of E. multiocellata in winter (hibernation), spring (emerging from hibernation), and summer (active) according to histomorphometry and the expression of genes such as those encoding aquaporins (AQP1, AQP2, AQP3), the Na+-Cl- cotransporter (NCC), the Na+-K+-2Cl- cotransporter (NKCC2), renin (Ren), angiotensin II receptor type 2 (AT2R), and endothelial nitric oxide synthase (eNOS) in the kidneys. The results showed that the area of Bowman's capsule and the glomerular density were lower in winter compared to summer and spring, and the lumen size of the DCT, PCT, and IS was greater in spring than in summer. Compared to summer and spring, the expression of AQP1, AQP3, NCC, NKCC2, Ren, and eNOS was significantly decreased in winter, whereas the expression of AQP2 and AT2R remained high. These results indicate that E. multiocellata balances its water budget via morpho-functional changes in different seasons. Although renal function was temporarily attenuated during winter, the regulation of aquaporins genes was not synchronous, indicating the complexity and particularity of water and salt regulation in desert lizards when facing the constraints of harsh environmental conditions, seasonal variations, and hibernation. These results will enrich the understanding of water and salt regulation mechanisms in desert reptiles.

Biomimetic lizard robot for adapting to Martian surface terrain.

The exploration of the planet Mars still is a top priority in planetary science. The Mars surface is extensively covered with soil-like material. Current wheeled rovers on Mars have been occasionally experiencing immobilization instances in unexpectedly weak terrains. The development of Mars rovers adaptable to these terrains is instrumental in improving exploration efficiency. Inspired by locomotion of the desert lizard, this paper illustrates a biomimetic quadruped robot with structures of flexible active spine and toes. By accounting for spine lateral flexion and its coordination with four leg movements, three gaits of tripod, trot and turning are designed. The motions corresponding to the three gaits are conceptually and numerically analyzed. On the granular terrains analog to Martian surface, the gasping forces by the active toes are estimated. Then traversing tests for the robot to move on Martian soil surface analog with the three gaits were investigated. Moreover, the traversing characteristics for Martian rocky and slope surface analog are analyzed. Results show that the robot can traverse Martian soil surface analog with maximum forward speed 28.13 m s-1turning speed 1.94° s-1and obstacle height 74.85 mm. The maximum angle for climbing Martian soil slope analog is 28°, corresponding slippery rate 76.8%. It is predicted that this robot can adapt to Martian granular rough terrain with gentle slopes.