LILLYWHITE, H.B.; TU, M.C.: First Ecdysis Increases Skin Resistance to Evaporative Water Loss in Newborn Snakes
Aquatic-terrestrial transitions associated with nativity present numerous physiological challenges for terrestrial vertebrates, one being the requirement to limit excessive losses of water due to evaporation. Epidermal water barriers comprised of lipids prevent excessive water loss in the adults of most species, but little is known about developmental mechanisms that establish or regulate these barriers. Newborn snakes typically shed their epidermis within a few days following birth, and behavioral changes are associated with this event. We employed 20 newly hatched California king snakes (Lampropeltis getula) to test the hypothesis that the first ecdysis is important for establishing the epidermal barrier to cutaneous water loss (CWL). We measured CWL within three days of hatching and again at three days following the first ecdysis (9-14 days post hatching). Rates of CWL were quantified using a RH/Dew Point meter to measure water vapor density in partially saturated air flowing through an acrylic tube with and without a snake present. Each snake was anesthetized to eliminate movements and to minimize respiratory water loss. Boundary layer resistance was negligible in the conditions of our experiments. We found that CWL was significantly lower (37.1 � 1.2 vs. 66.1 � 4.3 µg/cm2*h), and skin resistance higher (1118.2 � 37.9 vs. 596.0 � 31.6 s/cm), following the first ecdysis (P<0.0001). Such changes might explain the reclusive behaviors of newborn snakes and might also terminate parental care of newborn pit vipers that disperse away from parents following the first ecdysis. We are investigating this phenomenon in pit vipers as well as the likelihood that increases in cutaneous resistance are related to the deposition of lipids within the epidermis.
