A comparative behavioural and structural study of rain-harvesting and non-rain-harvesting agamid lizards of Anatolia (Turkey)

Some lizards living in arid or semi-arid habitats have developed a specific adaptation to capture and drink water. This adaptation, rain-harvesting, occurs when water is carried through interscalar channels between integumental scales to the mouth, the point where water is ingested. We investigated whether this special water-drinking adaptation is utilized in four species of agamid lizards living in Turkey Stellagama stellio (Linnaeus, 1758), Paralaudakia caucasica (Eichwald, 1831), Trapelus lessonae (De Filippi, 1865) and Phrynocephalus horvathi (Mehely, 1894). Using histological and scanning electron microscopic methods, we found that P. horvathi has the integumental adaptations to rain-harvest water; however, S. stellio and P. caucasica do not. Determination of the rain-harvesting condition in T. lessonae will require further research. In all four species, honeycomb-shaped micro-structures cover dorsal scale surfaces, and in P. horvathi, a complex capillary system involving scale hinges was documented. In experiments with captive animals, which included putting dyed water drops onto the integument, we found that even the species that do not have ability to rain-harvest can collect water on their integuments. But in these species the water does not move into their mouth. Our new findings of rain-harvesting in P. horvathi are compared with published data to show that this specific adaptation has evolved convergently with other agamids and with iguanids. Also water flow within the scale hinge system of P. horvathi is directional, towards the head.