Meeting Abstract
In birds, the last step of egg formation is deposition of eggshell which provides a physical barrier for embryos. A match among eggshell characteristics, embryonic demand for gas exchange through pores, loss of water through pores, and environmental condition are critical in proper embryonic development as the metabolic rate of embryos and the demand for greater gas exchange both increase when embryos develop under high temperatures. Recent studies have shown that eggshell characteristics are under natural selection in birds which recently colonized new environments with different temperature and humidity compared to ones in the source population. However, maternal control of eggshell characteristics in response to environmental changes is largely unknown. We hypothesized that eggs whose mothers were exposed to heat while young would have greater pore densities and lower thicknesses to allow for greater gas transfer with the outside air. Towards the end, the goals of this study were to investigate whether thermal environment of mothers as juveniles and/or right before egg laying determined the eggshell thickness and pore density of the eggs they lay. Captive zebra finch females were divided into 4 groups in a fully factorial design where females experienced control (22C) or mild heat (38C) for 28 days during the juvenile period and control (22C) or high heat (42C) for 3 consecutive days as an adult. We found that only the pore density was subject to the thermal environment of the mother, with mothers exposed to heat treatment both as juveniles and adults producing eggs with the greatest pore density, and surviving offspring exhibiting greater pore densities. These results suggest that mothers have the ability to adjust eggshell characteristics so eggs are better adapted to the predicted thermal environment.
