Corticosterone stimulates hatching of late-term tree lizard embryos

Abstract

The regulation of hatching in oviparous animals is important for successful reproduction and survival, but is poorly understood. We unexpectedly found that RU-486, a progesterone and glucocorticoid antagonist, interferes with hatching of viable tree lizard (Urosaurus ornatus) embryos in a dosedependent manner and hypothesized that embryonic glucocorticoids regulate hatching. To test this hypothesis, we treated eggs with corticosterone (CORT) or vehicle on Day 30 (85%) of incubation, left other eggs untreated, and observed relative hatch order and hatch time. In one study, the CORT egg hatched first in 9 of 11 clutches. In a second study, the CORT egg hatched first in 9 of 12 clutches, before vehicle-treated eggs in 10 of 12 clutches, and before untreated eggs in 7 of 9 clutches. On average, CORT eggs hatched 18.2h before vehicle-treated eggs and 11.6h before untreated eggs. Thus, CORT accelerates hatching of near-term embryos and RU-486 appears to block this effect. CORT may mobilize energy substrates that fuel hatching and/or accelerate lung development, and may provide a mechanism by which stressed embryos escape environmental stressors.

Hormonally mediated maternal effects shape offspring survival potential in stressful environments

“…Accordingly, the observed cortisol-induced eVects may represent an adaptive mechanism by which mothers communicate information about the prevailing environment to their oVspring to ensure their immediate survival. Similar hormonally mediated maternal eVects that induce a transition between life stages to avoid deadly conditions or deteriorated environments have been demonstrated in mammals, amphibians and reptiles (Denver 1997;Crespi and Denver 2005;Weiss et al 2007), illustrating the beneWcial eVects of maternal glucocorticoids in shaping the neuroendocrine responses of oVspring, albeit at the potential cost of reduced Wtness later in life.…”

Stress and Reproduction in Reptiles

“…Radder et al (2008) posited that the observed premature oviposition by CORT-treated females might be adaptive in terms of protecting the eggs from the possible harmful effects of CORT. The implication of this finding is that tree lizards are unlikely to develop to fullterm in extremely high-CORT environments (Weiss et al, 2007). There is also evidence that super-physiological levels of CORT present in egg yolk at the time of oviposition reduce hatching success in U. stansburiana (Johnston & Moore, unpublished data; Lucas & Weiss, unpublished data; both cited in Weiss et al, 2007), a finding that was attributed to the gross detrimental effects of CORT on the embryo rather than on the hatching event itself (Weiss et al, 2007).…”

“…At oviposition, CORT-treated females had significantly higher CORT levels (mean ¼ 246.2 ng/ml) than did control females (79.0 ng/ml), although CORT levels in the egg yolk of offspring were unaffected by maternal treatment. There is also evidence that super-physiological levels of CORT present in egg yolk at the time of oviposition reduce hatching success in U. stansburiana (Johnston & Moore, unpublished data; Lucas & Weiss, unpublished data; both cited in Weiss et al, 2007), a finding that was attributed to the gross detrimental effects of CORT on the embryo rather than on the hatching event itself (Weiss et al, 2007). On the other hand, in the side-blotched lizard, U. stansburiana, treatment of gravid females with a low dose (imitated high-end baseline physiological levels) or a high dose (imitated stress-related levels; i.e., equal to or greater than double baseline levels) of CORT delivered from implants did not accelerate or delay the timing of egg laying .…”

“…The effects of treating oviposited eggs with CORT rather than treating gravid females have been studied in the tree lizard, U. ornatus (Weiss et al, 2007). The rationale behind this study was the unexpected finding that RU-486, a P 4 and glucocorticoid antagonist, when given to nearly full-term embryos adversely affected hatching success in a dose-dependent manner.…”

“…The rationale behind this study was the unexpected finding that RU-486, a P 4 and glucocorticoid antagonist, when given to nearly full-term embryos adversely affected hatching success in a dose-dependent manner. Based on this discovery, Weiss et al (2007) suggested that CORT produced in the embryo in response to environmental stressors might mobilize the energy stores needed to fuel hatching and/or to stimulate lung maturation and thus accelerate the timing of hatching in U. ornatus. These investigators found that oviposited eggs that were treated with CORT on day 30 of incubation hatched significantly sooner than vehicle-treated eggs and untreated eggs.…”