Assessments of genetic and reproductive health in Canada’s endangered Oregon Spotted Frog (Rana pretiosa)
Date
2023-08-04
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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.