Assessments of genetic and reproductive health in Canada’s endangered Oregon Spotted Frog (Rana pretiosa)

Abstract

Zoological institutions are increasingly relied upon for ex situ management of species at risk, with conservation breeding and reintroduction programs providing both assurance against extinction and a reliable source of offspring to reinforce wild population sizes. Ex situ efforts face many challenges, however. One often overlooked challenge is balancing genetic priorities, like retaining genetic diversity and reducing inbreeding, with reproductive priorities, like mate compatibility and reliable breeding, both of which are required for a successful program. Like many amphibians, the Oregon Spotted Frog (Rana pretiosa) is highly threatened in its native habitat and ongoing conservation breeding and reintroduction programs are experiencing limited success; the genetic sustainability of these populations remains unassessed. In this study, I evaluated the genetic health of both zoo and wild populations of R. pretiosa in Canada and investigated some potential causes of the ongoing ex situ reproductive failures associated with egg binding. I found that zoos have maintained stable genetic metrics relative to their wild sources, but ongoing collections from wild populations should be reassessed due to low genetic diversity available therein. No clear causes of egg binding were elucidated but I found older female frogs (> 3 years old) who became egg bound generally had a higher body mass than conspecifics, while body mass did not differ in females becoming egg bound in their first breeding season (2-3 years old). This suggests frogs should be monitored for egg binding and changes in body condition differently depending on their age. Overall, there were no significant differences in genetic or reproductive health across the three zoo conservation breeding populations, but scaled mass index was significantly lower in the zoo with larger holding tanks and less genetic management: a reminder of the importance of husbandry and environment in conservation breeding program outcomes. The costs and benefits of strict genetic management vs. a more communal breeding approach should be carefully considered in light of these results. Along with more cohesion, communication is required between all involved institutions to have an effective impact on the conservation of Oregon Spotted Frogs in Canada, the recommendations discussed here have applicability to amphibian ex situ programs worldwide.