Can Geckos Increase Shedding Rate to Remove Fouling?

Abstract

All vertebrates shed the outer layer of their epidermis, usually continuously, but squamate reptiles shed periodically, losing large pieces of this layer at once. While the cellular processes leading to loss of the outer epidermal layer, or shedding, in squamates have been studied in detail, few studies have examined the factors associated with shedding frequency. Shedding is an obligate event, linked to somatic growth and the regeneration of damaged or worn epidermal areas. Another proposed role for periodic shedding in squamates is the removal of ectoparasites and fouling substances stuck on the epidermis. It is unclear whether the removal of ectoparasites and fouling substances is completely passive, only mediated by a fully obligate shedding cycle, or if shedding can be mobilized directly in response to parasite attachment or fouling. To test these hypotheses, we first assessed whether shedding reduced the adherence of parasites to the skin of six different species of geckos by counting mites on the outer epidermis before and after shedding events. Next, we assessed whether shedding was triggered by fouling. Using four species of geckos, we applied artificial substances (marker pen [Sharpie^TM], and wood glue [polyvinyl acetate]) to the outer layer of the epidermis and recorded the time between shedding events (shedding interval) compared to unmanipulated controls. There was a clear decrease in parasite loads after shedding events, confirming that shedding reduces adherence of parasites. Our experiments with artificial substances applied to the outer epidermis showed that most gecko species did not change their shedding intervals, regardless of skin-fouling treatment. <i>Hemidactylus frenatus</i>, however, decreased their shedding interval in response to the application of wood glue. Thus, we found that parasites, if present, are removed by shedding, and external fouling can trigger shedding at least in one species of gecko.