Conductance and Structure of Eggs of Adelie Penguins, Pygoscelis Adeliae, and Its Implications for Incubation’

Structure and conductance of eggshells of Adelie Penguins, Pygoscelis adeliae, were studied to address the question: How is the eggshell adapted to cope with the extreme aridity of the Antarctic, and in particular, what is the significance and function of the organic cuticle on the eggshell? Adelie Penguin shell structure has a basic avian pattern with relatively straight, unbranched pores that are occluded by an organic cuticle on the outside of the shell. Mean shell conductance of 15.4 mg.day-l .Torr-’ of six intact eggs is significantly lower than one would predict on the basis of fresh egg mass, and conductance after cuticle removal (18.6 mg day-l. Torr+) from three eggs is significantly higher. Theoretical consideration of tensions of 0, and CO, in intact eggs and cuticle-removed eggs indicates that, whereas 0, tensions inside the egg may not be stressful to the embryo prior to hatching if the cuticle remained intact throughout incubation, CO, tensions may be. We conclude that the cuticle reduces loss of water during the early part of incubation, but that its erosion during incubation increases conductance thereby maintaining CO, tensions close to levels expected in eggs of this size. Calculations of functional pore radius from conductance measures for cuticle-removed eggs are almost identical to real mean pore radius measured from pore casts.