Shell Conductance, Daily Water Loss, and Water Content of Puna Teal Eggs

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Abstract
Characteristics of Puna teal (Anas versicolor puna) eggs laid at 4,150 m in the Peruvian Andes were compared with those of similarly sized eggs laid by other Anas species at sea level Mean eggshell conductance to water vapor (GH₂O, corrected to 760 Torr) was reduced below the average of most of the sea-level controls, but not to the same extent as the reduction in barometric pressure at the breeding site. In contrast to findings of previous studies, the reduction in GH₂O was not significant in three of four comparisons. Since the diffusion coeficient for water vapor increases inversely with barometric pressure, water loss during incubation was high, but relative water content of the eggs did not vary significantly during incubation. Variation in shell conductance was most likely due to alteration in the number of pores rather than to size. The characteristics of montane Puna teal eggs appear to reflect selection by conflicting requirements for preventing excessive loses of water vapor and CO₂ and for maximizing O₂ availability to the embryo.