Steroid levels in frog eggs: Manipulations, developmental changes, and implications for maternal steroid effects

Abstract

Exposure to maternally derived steroids during embryonic development can elicit phenotypic effects in the resulting offspring. Studies of maternal steroid effects, especially rich in mammals and birds, have offered exciting insights into the evolution of maternal effects in vertebrates. To extend this literature, we quantified levels of steroids in the eggs of four neotropical dendrobatid frogs that lay terrestrial clutches, a reproductive strategy that has evolved multiple times in amphibians.Building on our observational results, we then manipulated levels of pregnenolone and progesterone in eggs of one species and examined how this affected steroid levels during development. Eggs of all four species had detectable steroids levels, with progestogens being more abundant than androgens and glucocorticoids. Estrogens could not be detected. Immersion of frog eggs in a solution containing pregnenolone and progesterone resulted in elevated levels of both steroids early in development, but levels declined and were similar to those in unmanipulated eggs by the end of development. Treated eggs also exhibited a transient increase in levels of steroids that can be produced from pregnenolone and progesterone. Overall, our findings demonstrate that frog eggs contain steroids similar to what has been observed in other egg-laying vertebrates. During development, steroid levels are dynamic, further suggesting developing embryos regulate exposure to maternal steroids. These results set the stage for investigating the causes and consequences of maternal steroid effects in frogs.

Tadpole plasticity shapes the potential benefits of egg feeding to poison frog parents

“…Feeding both focal species with heterospecific “trophic eggs” removed any potential advantages one focal species might enjoy by consuming eggs produced by conspecific females. These eggs are qualitatively similar in size to those of both Ranitomeya , but differences in their nutritional content and/or other maternal effects (e.g., steroids: Paitz & Dugas, 2022) might affect tadpoles of the two species differently, and in unknown ways.…”

The effects of preformed vitamin A and provitamin A carotenoid supplementation on tadpoles of the poison frog Phyllobates vittatus

“…Tadpoles are uniformly dark brown on the dorsal side, and are lighter brown ventrally, and gradually develop orange dorsolateral stripes, starting around Gosner stage 37 (Gosner, 1960). Metamorphosis occurs approximately 10 weeks after hatching (Paitz & Dugas, 2022; Savage, 2002; R. Márquez pers. obs.…”