title: Informing Management Strategy for the Relict Leopard Frog (Rana onca): Insights Into Breeding Biology and an Attempt to Improve Augmentation Success Through Pre-Exposure and Clearance of an Emerging Amphibian Pathogen
Creators: name: Rivera, Rebeca
Publisher: name: University of Nevada, Las Vegas
publisherIdentifier: https://ror.org/0406gha72
publisherIdentifierScheme: ROR
Year: 2023

description: The Relict Leopard Frog, Rana onca, is a species of conservation concern that suffered a decline sometime during the 20th century. Even after two decades of intensive management, the species currently only occupies 20 spring sites in southern Nevada and northwestern Arizona. The causes for the historical decline are mostly speculative, but relate to habitat loss, introduced predators, and emergent disease. Since 2001, R. onca has been under an intensive conservationprogram managed by a multiagency conservation team. There are several objectives specified in the program including the need to investigate the biology of the species and incorporate findings into management strategies. Presented in this thesis are two research projects intended to inform management of R. onca, including a life history assessment of breeding biology, and a proof-of concept assessment aimed at improving survival of headstarted frogs in a landscape where an emergent amphibian pathogen is present.
The first project, on the breeding biology of R. onca, was initiated because there was limited information on the topic, with only a few summaries published in the literature and other information buried in relatively inaccessible government reports. Data on breeding biology were accumulated from 19 years of headstarting, translocation, and population monitoring efforts. To add new insights and clarify previous perspectives, this information was synthesized and assessed to determine breeding seasonality, egg mass size, time to hatching, time to metamorphosis, and time to reproductive maturity. In an iterative process, the knowledge gained on breeding biology was incorporated over time to improve the conservation program for the species.
The historical decline of R. onca may have been facilitated by the emergence of the amphibian disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd). The second project was a proof-of-concept to determine if pre-exposure to Bd followed by clearance of infections (pre-exposure and clearance) improved survival in headstarted R. onca
used to augment a population where the pathogen was present. The study incorporated 229 headstarted frogs separated into two groups, a group that underwent pre-exposure and clearance, and a control group treated identically but exposed to a sham inoculum. The groups were released to a study site where Bd was present and then monitored for subsequent infection and survival over 18 months. Mark-recapture and generalize additive modeling were used to analyze field data. Infection prevalence and intensity across treatment groups were predicted by survey date and air temperature, with Bd infections in frogs showing strong seasonal trends. The pre-exposure group had improved resistance at important points in time and showed a trend of moderately higher survival then the control group, although the difference in survival was not
statistically supported. The findings from this research inform managers on the practicality of using pre-exposure and clearance on headstarted R. onca intended for release at sites with Bd, as well as provides insight into the potential dynamics of this amphibian pathogen in the southern Nevada region.