Evaluation of different temporal periods between hormone-induced ovulation attempts in the female Fowler’s toad Anaxyrus fowleri

Authors: GUY, EMMET - Mississippi State University; MARTIN, MICHELLE - University Of Memphis; KOUBA, ANDREW - Mississippi State University; COLE, JUDITH - University Of Memphis; VANCE, CARRIE - Mississippi State University

Submitted to: Conservation Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2019
Publication Date: 12/11/2019
Citation: Guy, E., Martin, M., Kouba, A., Cole, J., Vance, C. 2019. Evaluation of different temporal periods between hormone-induced ovulation attempts in the female Fowler’s toad Anaxyrus fowleri. Conservation Physiology. 8(1):1-8.

Interpretive Summary: Seasonal patters in animal breeding behavior, endocrinology and fecundity can have profound consequences in total reproductive output. Overcoming seasonal limits in reproductive cyclity would provide enhanced control over annual cycles in animal reproduction. Using our model vertebrate species we can examine the link between season and the response period between breeding events. Using Quantum-dot nanoparticles conjugated to reproductive hormones we can follow the seasonal expression of hormone receptors and their responses to repeated stimuli in ovarian cycling. in living systems and real time. Several anuran species undergo a second wave of egg production soon after breeding which could be exploited to increase numbers of offspring. In this study, non-hibernated Fowler’s toads produced fertilizable oocytes after a four month refractory period without significantly impacting the number of ovulating females, total egg production, or egg quality.

Technical Abstract: Many amphibian species reinitiate the processes of preparing for reproduction (e.g. oogenesis) soon after breeding indicating hormone-induced ovulation could potentially be achieved out-of-season, which would lead to higher annual fecundity compared to mono-seasonal breeding. Such strategies would be beneficial to captive breeding programs for threatened species that are short-lived, have aging populations, or need large numbers of offspring to meet reintroduction goals for species recovery. Unfortunately, little is known regarding how female anurans respond to multiple ovulation events within a year, which could lead to higher annual fecundity compared to mono-seasonal breeding. Thus, we evaluated the effect of temporal period between exogenous hormone stimulation events on egg production using the Fowler’s toad Anaxyrus fowleri as a model species. Female toads (n = 21) were administered hormone therapy twice in one year with toads randomly assigned to a treatment of either a 4, 8, or 12 month recovery period between hormone stimulations. Ovulation was induced using two priming doses of human Chorionic Gonadotropin (100 IU; hCG) 72 hours apart, followed by a resolving dose of hCG (500 IU) plus gonadotropin releasing hormone analog (GnRHa; 15 µg) given 24 hours after the second priming injection. Measured response variables include the number of females ovulating after treatment, total number of eggs produced, and percent fertilization, neurula, and tadpole development. No significant treatment effects were observed for any response variable (p > 0.05). Findings from this study suggest hormone therapy can be administered in a bufonid species every 4 or 8 months withoutsignificantly affecting the number of ovulating females, egg production, fertilization, neurulation, or tadpole development. By collecting gametes out-of-season or multiple times throughout the year, captive breeding programs could potentially increase tadpole production for reintroductions as well as extend the breeding window in captivity.