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The Effects of Elevated Water Conductivity on Larval Eastern Hellbender (Cryptobranchus a. alleganiensis) Survival, Development, Locomotor Performance, and Physiology

Mathes, Samuel Casey
http://orcid.org/0009-0001-5766-9640
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1713449863713479

Abstract Details

2024, Master of Science (MS), Ohio University, Biological Sciences (Arts and Sciences).
Eastern Hellbenders (Crytobranchus a. alleganiensis) have suffered enigmatic, range- wide declines over the past decades. Persisting populations are skewed towards larger, older adults, suggesting that reduced recruitment is responsible for these declines, with degraded water quality, specifically elevated conductivity, implicated as a main contributor. Successful fertilization and the resilience of eggs under high conductivity conditions suggest deleterious effects during larval development. We experimentally assessed the effects of chronic exposure to elevated conductivity (1000 μS/cm) on wild Eastern Hellbender larvae hatched in a lab, as well as the effects of switching from low conductivity (100 μS/cm) to high, and vice versa, on Eastern Hellbenders during early larval development. We assessed mortality over 72 days post-hatching, with half of the larvae switched from their original conductivity treatments to the other over five days beginning at 33 days post-hatching. Chronic exposure to elevated conductivity resulted in significant mortality. Additionally, switching larvae from low conductivity to high resulted in increased mortality, while switching larvae from high conductivity to low increased survival. We also assessed larval morphology and swimming performance and found significant negative effects of chronic exposure to elevated conductivity on both body mass and multiple measures of morphology (length and width). We observed similar effects in animals switched from low conductivity to high, while switching animals from high conductivity to low resulted in only marginally increased mass and morphological measures, demonstrating their inability to compensate for initially depressed growth rates even after being returned to more optimal conditions. Despite altered size and morphology, elevated conductivity did not impact locomotor performance, though switching conductivities, regardless of direction, did result in increased burst distance. We measured whole-body cortisol at the end of the experiment as a measure of overall stress and found no differences across treatment groups, potentially due to the incomplete formation of the hypothalamic-pituitary-adrenal (HPA) axis during early larval development. We also measured lipid peroxidation, a marker of oxidative stress, and while not significant, we did observe increased lipid peroxidation in larvae chronically exposed to elevated conductivity. Furthermore, switching larvae from low conductivity to high similarly increased lipid peroxidation, while switching larvae from high conductivity to low resulted in decreased lipid peroxidation. In a preliminary analysis designed to explore the mechanisms underlying the inhibited growth we observed in larvae exposed to elevated conductivity, we leveraged transcriptomic information from the Chinese Giant Salamander (Andrias davidianus) to quantitatively evaluate the expression of growth-related genes in Eastern Hellbenders. While not significant, we observed consistently downregulated growth hormone (gh), growth hormone receptor (ghr), and prolactin receptor (prlr) messenger RNA (mRNA) transcripts in larvae chronically exposed to elevated conductivity. Additionally, these transcripts were consistently upregulated in larvae switched from high conductivity to low, and conversely, downregulated in those switched from low conductivity to high, suggestive of some effect of conductivity in modulating the expression of these growth conferring genes, possibly independent of hypothalamic control. The results of this study suggest that elevated conductivity has profound effects on larval Eastern Hellbenders and should be considered a critical metric relating persistence of self-sustaining populations to water quality.
Shawn Kuchta (Advisor)
Viorel Popescu (Committee Member)
Kelly Johnson (Committee Member)
106 p.
Biology; Conservation; Ecology; Endocrinology; Freshwater Ecology; Molecular Biology; Morphology; Organismal Biology; Wildlife Conservation
Eastern Hellbender; conductivity; larvae; survival; growth; development; locomotor performance; physiology; morphology; salinity; stress; cortisol; lipid peroxidation; recruitment; salamander; amphibian

Recommended Citations

Citations

  • Mathes, S. C. (2024). The Effects of Elevated Water Conductivity on Larval Eastern Hellbender (Cryptobranchus a. alleganiensis) Survival, Development, Locomotor Performance, and Physiology [Master's thesis, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1713449863713479

    APA Style (7th edition)

  • Mathes, Samuel. The Effects of Elevated Water Conductivity on Larval Eastern Hellbender (Cryptobranchus a. alleganiensis) Survival, Development, Locomotor Performance, and Physiology. 2024. Ohio University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1713449863713479.

    MLA Style (8th edition)

  • Mathes, Samuel. "The Effects of Elevated Water Conductivity on Larval Eastern Hellbender (Cryptobranchus a. alleganiensis) Survival, Development, Locomotor Performance, and Physiology." Master's thesis, Ohio University, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1713449863713479

    Chicago Manual of Style (17th edition)

ohiou1713449863713479
© 2024, all rights reserved.
This open access ETD is published by Ohio University and OhioLINK.
Release 3.2.12