Master of Science degree with a major in Biology
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The life history of a species is described in terms of its growth, longevity, and reproduction. Unsurprisingly, life history traits are known to vary in many taxa across environmental gradients. In the case of amphibians, species at high elevations and latitudes tend to have shorter breeding seasons, shorter activity periods, longer larval periods, reach sexual maturity at older ages, and produce fewer and larger clutches per year.
The Coastal Tailed Frog (Ascaphus truei) is an ideal species for the study of geographic variation in life history because it ranges across most of the Pacific Northwest from northern California into British Columbia, and along its range it varies geographically in larval period and morphology. During a California Department of Fish and Wildlife restoration project in the Trinity Alps Wilderness, I had incidental captures of Coastal Tailed Frog larvae and adults. To date, no population across the species’ range has been described above 2000m. These populations in the Trinity Alps range from 150m to over 2100m in elevation, and those that are in the higher part of the range are likely living at the species’ maximum elevational limit.
In this study, I examined size, growth, larval period, size at sexual maturity, and longevity of A. truei across populations along an elevational gradient in the Klamath Mountains of northern California. I calculated growth rates and movement by individually marking tadpoles and post-metamorphic frogs with visual implant elastomer (VIE), then tracking them from May through October of 2018. I described the length of the larval period using length-density histograms to visualize larval cohorts, I determined size at sexual maturity using secondary sexual characteristics of post-metamorphic frogs, and I determined longevity using skeletochronology.
I found that the larval period of A. truei in the Klamath Mountains of northern California ranges from two years in low and mid-elevations, to at least three years in high elevations. I also found decreased body size and increased growth rates of tadpoles with increasing elevation. Post-metamorphic frogs grew at similar rates as previously described coastal California populations. There was high site fidelity and significantly greater movement during the months of June and August in post-metamorphic animals. Frogs in the high elevations are capable of great longevity, with a maximum observed age estimated at eight years post-metamorphosis.
The high elevation populations described here have the longest larval period documented in California. This study also provides the first field estimates of larval growth rates and the first longevity estimates of post metamorphic frogs in California. Future laboratory experiments will be necessary to separate phenotypic plasticity of life history traits from true genetic differences between A. truei populations in the Klamath Mountains of northern California, as potential explanations for the variation seen.
Journal of Wildlife Management
Macedo, Adrian Daniel, "Life history of the coastal tailed frog (Ascaphus truei) across an elevational gradient" (2019). HSU theses and projects. 330.