Effects of Sheel Closure on Water Loss in the Sonoran Mud Turtle, Kinosternon sonoriense

Abstract

Semi-aquatic turtles of the genus Kinosternon have two well-developed hinges in the plastron which permit the shell to be closed following withdrawal of the head and limbs. Species having broad, extensive plastrons are able to close their shells more completely than those with reduced plastrons, and some species exhibit a clinal increase in relative plastron size that correlates positively with increased degree of terrestrialism (Iverson, 1978). Complete shell closure should be adaptive in retarding dehydration during terrestrial exposure because such closure sequesters the more permeable epidermis of the soft parts and leaves exposed to the atmosphere only the less permeable epidermis of the shell (Spotila and Berman, 1976; Seidel and Reynolds, 1980). Seidel and Reynolds (1980) attributed the lower evaporative water loss rates they measured for Kinosternon alamose and Kinosternon integrum than for Kinosternon flavescens and Kinosternon hirtipes to the ability of the former species to completely close their shells. However, this hypothesis remains tentative because it is not known to what