WEISS, SL; JOHNSTON, G; MOORE, MC; Arizona State Univ, Tempe; Arizona State Univ, Tempe; Arizona State Univ, Tempe: Corticosterone stimulates hatching of tree lizard embryos

The regulation of hatching behavior in oviparous animals is important for successful reproduction, but is poorly understood. We have been investigating the endocrine regulation of hatching behavior in oviparous tree lizards. Based on our previous results that (1) RU-486, a progesterone- and glucocorticoid-receptor antagonist, interferes with hatching of viable lizard embryos and (2) lizard embryos secrete glucocorticoids during pre-hatching development (Jennings et al, 2000), we hypothesized that endogenous glucocorticoids stimulate embryonic hatching behavior. To test this hypothesis further, in 2003 we treated pairs of eggs from 12 clutches with either corticosterone (CORT) or vehicle on day 30 of incubation and observed relative hatch times. Tree lizards normally hatch around day 35 of incubation. The CORT treated egg hatched first in 9 of 12 clutches. In 2004, we used a video camera to more closely time hatching and we included an additional group of untreated eggs. Vehicle treatment alone does not stimulate hatching, as vehicle-treated eggs hatched before untreated eggs in only 3 of 10 clutches. The CORT egg hatched first in 9 of 12 clutches, hatched before vehicle-treated eggs in 10 of 13 clutches, and hatched before untreated eggs in 7 of 9 clutches. We standardized time to hatch by assigning the �first hatch� of each clutch to 0 min. On average, CORT, vehicle, and control eggs hatched at 58, 1055, and 736 min respectively (P<0.01). Combined, these data suggest that CORT is involved in stimulating the behavior required for hatching to occur. CORT may help to mobilize the energy substrates required to support this strenuous activity and/or it may provide a mechanism by which stressed embryos can hatch earlier to try to escape a stressor, similar to what has been described for amphibian metamorphosis.