Influence of oviposition-inducing hormone on spawning and mortality in the endangered Panamanian golden frog (Atelopus zeteki)

Authors: BRONSON, ELLEN - Maryland Zoo; GUY, EMMET - Mississippi State University; MURPHY, KEVIN - Maryland Zoo; BARRETT, KEVIN - Maryland Zoo; KOUBA, ANDREW - Mississippi State University; POOLE, VICKY - Fort Worth Zoo; KOUBA (VANCE), CARRIE - Mississippi State University

Submitted to: BMC Zoology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2021
Publication Date: 5/22/2021
Citation: Bronson, E., Guy, E.L., Murphy, K.J., Barret, K., Kouba, A.J., Poole, V., Kouba 9vance), C.K. 2021. Influence of oviposition-inducing hormone on spawning and mortality in the endangered Panamanian golden frog (Atelopus zeteki). BMC Zoology. 6(17), pp.1-14. https://doi.org/10.1186/s40850-021-00076-8.
DOI: https://doi.org/10.1186/s40850-021-00076-8

Interpretive Summary: There are two problems frequently encountered in assisted breeding of animals; first is that females with eggs often do not express them, and second, that a female with eggs may undergo a fatal condition of egg binding and sepsis. This project aimed to develop induced ovulation and health management protocols using different doses of egg inducing hormones and determining latency periods and the effects of pulsed hormone sequences in promoting egg laying while simultaneously avoiding egg-associated mortality in valuable females. Using amphibians as a model to birds and fish species of interest in agriculture and aquaculture, we demonstrate hormone application significantly decreased mortality rates of gravid females compared to those that remained untreated by correcting egg binding that contributes to the detrimental health effects from extended breeding efforts. Moreover, sharing information with the community that the death rate is not a function of hormone administration is valuable for adoption of these techniques. The knowledge generated from this reproductive study has helped develop best management practices for the application of hormone therapy and assisted reproductive technologies for the critically endangered amphibians with application to agriculturally and medically important species. Future research is needed to determine if alternative hormones can increase egg production rates while further decreasing mortality.

Technical Abstract: With Panamanian golden frogs (Atelopus zeteki; PGFs) likely extirpated from the wild, ensuring longterm sustainability of captive populations is crucial in order to conserve this critically endangered species. Unfortunately, PGFs display a unique reproductive behavior involving a prolonged period of amplexus leading to challenges in their successful captive propagation. The Maryland Zoo in Baltimore has observed high levels of mortality during the breeding season and suboptimal reproductive success leading to the use of hormone stimulation to aid in reproduction and health management. This project aimed to develop induced ovulation and health management protocols by (1) evaluating different doses of gonadotropin releasing hormone analogue (GnRHa), (2) comparing the efficacy of GnRHa and GnRHa + metoclopramide, (3) determining latency periods and the effects of pulsed hormone sequences; and (4) establish if mortality is impacted by hormone therapy. Female PGFs (n = 174) were given GnRHa either in various concentrations (Experiment 1) or combined with metoclopramide (Experiment 2), and oviposition success, latency, and mortality were measured as binary response variables. Results: Overall, the use of exogenous hormones significantly decreased mortality when compared to the control data of natural egg-laying females. GnRHa doses of 0.05 µg/g body weight produced similar ovulation rates compared to higher doses, and the addition of metoclopramide did not increase oviposition success compared to GnRHa alone. Lastly, results indicate the majority of female PGFs will release eggs within 48 h following the initial pulse of hormones with a small percentage ovipositing after a second pulse.Conclusion: Findings from this study will benefit captive management of PGFs by documenting the increased survival of females when given hormone stimulation and defining appropriate GnRHa doses and expected latency to spawning.