Water Relations of Chelonian Eggs

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Abstract
Eggs of painted turtles (Chrysemys picta) absorb water across that portion of the eggshell in contact with the substrate and simultaneously lose water by transpiration from that part of the eggshell exposed to air inside the nest chamber. Depending upon the rates of influx and efflux, eggs may experience increases or decreases in mass during incubation, or mass may remain essentially constant between oviposition and hatching. Water exchanges are especially sensitive to such factors as substrate water potential, relative surface exposed to the nest atmosphere, hydraulic conductance of the eggshell, and conductance of the eggshell to water vapor. Hatchlings emerging from eggs absorbing and storing large quantities of water are heavier than hatchlings emerging from eggs taking up smaller quantities of water from the substrate. Furthermore, water absorption equal to, or in excess of, water loss by transpiration assures that the original shape of the egg will be preserved, thereby guaranteeing that sufficient space is available within the egg for normal development of the embryo.