Meeting Abstract

22.1  Thursday, Jan. 3  Effects of Increased Yolk Corticosterone on Embryonic and Yolk Hormone Levels Throughout Incubation JOHNSTON, GIH*; SHAFFERY, HM; MOORE, MC; Arizona State University gjohnston@asu.edu

Recent studies have shown that steroids of maternal origin can be sequestered in egg yolk. However, what happens to these steroids during embryonic development is still unclear. How do yolk and embryonic hormone levels change during incubation, and are these hormone profiles altered according to maternal contribution of hormones? In this study we examined both the yolk and embryonic profiles for testosterone, estrogen, and corticosterone (CORT) in the tree lizard, Urosaurus ornatus. We compared the hormone profiles of eggs from females who were treated with CORT, and thus laid eggs with increased yolk CORT, to those from unmanipulated females. Eggs were tested on days 10, 20, and 30 of incubation, where the average incubation time is 34 days. We found that egg yolk from unmanipulated females had low CORT levels throughout most of incubation, with a sharp increase on day 30 which may help facilitate hatching. Surprisingly, we found that there was a large significant drop in yolk CORT from the treated eggs such that they were indistinguishable from controls by day 10 of incubation. Hence, even though the eggs were initially loaded with CORT, these high levels were gone at an early stage before 1/3 of incubation was completed. However, on day 30 egg yolk from treated females had less CORT than controls. This blunting of the CORT spike before hatching may explain why previous studies have found that offspring from treated mothers hatch later than controls. These data demonstrate how dynamic hormone levels can be throughout incubation.