Ultrastructural observations suggest that lipid material of lizard digital pads derives from degenerating cells in the inter-scale region

Abstract

Ultrastructural observations suggest that lipid material of lizard digital pads derives from degenerating cells in the inter-scale region. Acta Zoologica (Stockholm). Production of epidermal lipids in lizards occurs in mesos- and alpha-layers, including those present in gecko adhesive pads. Lipid material is present over the setae and spatulae of adhesive pads where adhesion takes place. Lipids are hypothesized to influence the process of adhesion keeping hydrophobic the spatula that contacts the substrate. The origin of lipids in pad lamellae that are lost as footsteps during gecko movements is unknown. To maintain setae lipid-coated requires a large and continuous supply of lipids and the most likely source is an epidermal region rich in lipids. Ultrastructural observations show that lipid material is released from sloughed mesos and alpha-cells in the inter-scale region of the lamellae. It is hypothesized that lipids passively move from the hinge region and reach the outer lamella surface. Lipids may also derive from frictional damage of the thin alpha-cells located in the hinge regions during pad extension for climbing or moving on the substrate. The discharged lipid material is likely pushed out from the hinge region by progressive accumulation of secreted material. The present hypothesis presents a simple model illustrating lipid movement from inter-scale regions that coat the setae, contributing to the indicated influence of lipids on spatula adhesion.