Sperm quality metrics exhibit annual fluctuations in a critically endangered amphibian managed under human care

Abstract

The Puerto Rican crested toad (PRCT) is Puerto Ricos only endemic toad and has undergone rapid population decline within the last 40 years. As a hedge against extinction, captive assurance colonies have been established at several zoological institutions for breeding and reintroduction. However, reproductive output has remained low, despite the use of hormone therapies to attempt to bypass missing abiotic cues and stimulate reproductive behaviors. This low output necessitates a better understanding of natural fluctuations in gamete, specifically sperm, quality in captive individuals. To generate an understanding of natural gametic cycles in captive PRCTs, we administered male PRCTs (n = 86) housed under natural temperature and photoperiod cycles with exogenous hormones monthly for one year. Samples were analyzed for motility and concentration to assess variations in sperm quality by month. Spermiation was successfully stimulated every month, but quality fluctuated; sperm motility was highest in June and July, while sperm concentration was highest in December, January, and March. These results indicate that, while hormones can be utilized to stimulate gamete production in PRCTs year-round, sperm quality is not consistent. Furthermore, the seasonal occurrence of peak sperm production of captive males differed from natural peaks reported for wild PRCTs. Our results illustrate the need for more biologically informed strategies for breeding of at-risk anuran populations.