Amphibians are influenced by climate change, but we do not have a clear understanding of how changes in temperature, precipitation, or both, may influence amphibian larvae in temperate regions. Do amphibian larvae have similar developmental responses to increased temperature and increased drying rates of wetlands - both plausible effects of climate change? What influence do the interactive effects of temperature and drying have on the relationships between the larval responses themselves (e.g., survival, body size, and time to metamorphosis)? To address these questions, we studied larval responses of two amphibian species, wood frogs (<em>Lithobates sylvaticus</em>) and spring peepers (<em>Pseudacris crucifer</em>), to simulated warming and drying in experimental ponds. Over 13 weeks, we manipulated temperature and water levels in ponds to produce 4 treatments: control, drying, warming, and drying + warming. Our manipulations created warming treatments that were on average 2 ° C higher than controls, and our drying treatments decreased in water depth by 2.5 cm each week compared to warming and control treatments that held a consistent amount of water. In both species, warming treatments resulted in significantly earlier timing of metamorphosis, and drying treatments resulted in significantly reduced body size. We saw a negative relationship between body size and time to metamorphosis (i.e., individuals that metamorphosed faster generally had larger body sizes), indicating an unexpected decoupling of the typical positive relationship between time to- and size at metamorphosis. The strength of the relationship between responses also varied by treatment for wood frogs but not spring peepers, indicating that the responses of larval amphibians to climate change may vary among species. Our study reveals complex relationships among larval survival, body size, and time to metamorphosis and highlights the need for considering not only the role of interacting climate-related pressures on amphibians but also the mechanisms underlying coupling of larval responses to these pressures. We encourage future research and discussion on a better understanding of why different climate pressures caused different responses, and if these patterns may be consistent in other aquatic species. / Master of Science / Across the globe, shifts in temperatures and the availability of freshwater habitats due to climate change are presenting challenges as well as opportunities for many species, particularly those that rely on freshwater habitats to complete their life cycle. Climate change is leading to warmer water temperature and accelerated drying of wetlands and ponds. Warming and drying often occur simultaneously, yet our understanding of how warming and drying may interact and affect sensitive aquatic species is limited. Amphibians with an aquatic life stage (for example, frog tadpoles) are particularly vulnerable to the effects of climate change on wetlands and ponds because they must transform from swimming larvae to land-dwelling adults before aquatic habitats dry out. Warming and drying help amphibian larvae determine when to start that process, called metamorphosis. For this reason, amphibian larvae in aquatic habitats are especially vulnerable to shifts in water temperature and the timing of drying. In this thesis, I explore how warming and drying influence amphibian survival, body size, and time to metamorphosis. To better understand the responses of amphibian larvae to warming and drying, I tested the effects of warming and drying on three response variables: amphibian survival, body size, and time to metamorphosis. I used two different species, wood frogs and spring peepers, to determine whether frogs' responses vary among species. I created an artificial pond experiment where I filled large tanks to represent natural ponds in a controlled, outdoor setting. In these artificial ponds, I measured wood frog and spring peeper growth under experimentally increased water temperatures and accelerated drying levels over 13 weeks. I found a negative relationship between body size and time to metamorphosis, suggesting individuals who spent less time in the water as larvae were more likely to be larger than individuals who spent more time in the water as larvae. Additionally, ponds with higher larval survival were associated with larger body size and a shorter time to metamorphosis. Warmer water temperatures led to a shortened time to metamorphosis but did not always lead to higher body sizes. Accelerated drying did not lead to a shortened time to metamorphosis, but it did lead to smaller body sizes in both species compared to control and warming ponds. Overall, I found complex relationships among larval responses with the directions of responses varying between treatments and species. This highlights the need for considering the role of climate-related changes in the environment (warming and drying) as well as the interactions between specific larval responses to those environmental changes. By understanding how warming and drying influence amphibian larval success, we can make a more direct link between climate change and its effects on aquatic larvae. Incorporating the responses between survival, body size, and time to metamorphosis to gain a more complete understanding of amphibian larval responses to the changing climate is an important step toward conserving and protecting freshwater aquatic species.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110743 |
| Date | 17 December 2020 |
| Creators | Shadle, Elizabeth Jane |
| Contributors | Biological Sciences, Mims, Meryl C., Hopkins, William A., Lance, Stacey L., Belden, Lisa Kay |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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