Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Wildlife and Fisheries Resources
James T. Anderson
Sarah K. Woodley
Amy B. Welsh
James A. Thompson
Habitat creation is an important tool for conservation to counteract habitat loss and degradation. Vernal pools are susceptible to destruction due to limited detection, protection, and regulation. These wetlands provide fishless breeding habitat for many amphibian species including spotted salamanders (Ambystoma maculatum) in eastern North America. Determining whether created vernal pool habitat is successful is often determined by demographic data of colonizing populations. I suggest that hormone levels, population genetics, and disease prevalence can improve our understanding of population health in created habitat. The goal of this dissertation was to assess the health of spotted salamander larvae in created vernal pools quantified by corticosterone levels, genetic diversity and structure, and ranavirus prevalence. I also wanted to determine if there were habitat characteristics impacting these parameters to inform future construction techniques and produce habitat conducive to healthy colonizing amphibian populations.
I examined whether habitat traits influenced corticosterone levels of salamander larvae in created vernal pools. The strongest model predicting corticosterone levels included larval total length, pool-water temperature, year sampled, and pool diameter. Annual variation in corticosterone levels and habitat characteristics, and positive associations with water temperature and salamander body size highlighted the importance of controlling for external influences. The negative association between pool diameter and corticosterone indicated that larvae in larger pools (up to 12.75-m maximum diameter) were less stressed and potentially healthier.
Water-borne hormone sampling is relatively new to amphibians, so I attempted to biologically validate the method for spotted salamanders by comparing water-borne and plasma corticosterone concentrations of the same individuals. There were differences in corticosterone concentrations between larvae, metamorphs, and adults, but there were no correlations between water-borne and plasma concentrations for any of the age groups. The two sampling methods have different units of measurement which might affect the association between the two.
I evaluated the genetic structure and genetic diversity of spotted salamander larvae in created vernal pools. I also examined whether local habitat characteristics at the pool level influenced effective number of breeders, relatedness, or genetic diversity. The youngest pools exhibited genetic differentiation, founder’s effect, and low effective number of breeders. Effective number of breeders was positively associated with pool age, vegetation cover, pool diameter, and sample size. Pool cover and vegetation cover was also negatively associated with relatedness. Allelic richness and expected heterozygosity did not have strong environmental predictors.
I surveyed spotted salamander larvae in created vernal pools for ranavirus prevalence and measured viral load in individual larvae. I tested associations between ranavirus prevalence and viral load and habitat characteristics, genetic diversity, corticosterone levels, and body size. I detected ranavirus in 62% of pools in 84 of 1,128 larvae (7%). Prevalence at pools ranged from 0–63%. Salamanders infected with ranavirus had greater total length, which was also positively correlated with viral load. There were no associations between ranavirus prevalence or viral load and habitat characteristics, salamander genetic diversity, relatedness, effective number of breeders, or corticosterone levels.
These results indicate larger pool diameter (up to 12.75 m) and greater vegetation cover are important habitat traits to consider when creating vernal pool habitat for spotted salamanders. This research demonstrates that effective number of breeders can increase and genetic differentiation can decrease within 4–5 years of pool creation, a sign of rapid colonization and potential population establishment. The widespread occurrence of ranavirus in created pools illustrates the risk of disease exposure in newly created habitat; even with the generally low prevalence among salamanders in the majority of pools. The correlation between ranavirus and salamander total length could be a reflection of differences in susceptibility through developmental stages or increased risk of exposure over time.
This study contributes to the growing body of knowledge on the association between habitat quality and corticosterone levels and genetic diversity of amphibians. The disease surveillance will add a species and county record for West Virginia, contribute to current distribution maps, and document disease prevalence levels in created habitat. The results of this dissertation will help inform current management and future site selection and habitat creation by highlighting important habitat characteristics for spotted salamanders. Finally, this research illustrates the value of incorporating interdisciplinary approaches to assess the success of habitat creation and colonizing wildlife populations.
Millikin, Alice R., "Population Health of Spotted Salamanders (Ambystoma maculatum) in Created Vernal Pools: an Integrative Approach" (2019). Graduate Theses, Dissertations, and Problem Reports. 7461.
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