Date of Award:

5-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Susannah S. French (Committee Chair) Karen H. Beard (Committee Co-chair)

Committee

Susannah S. French

Committee

Karen H. Beard

Committee

Steven C. Hess

Abstract

The coqui frog (Eleutherodactylus coqui) is an invasive species in Hawai‘i, and has spread across much of the island. While elevational temperature differences are thought to restrict the coqui’s spread, it is unclear if they have resulted in changes to the coqui’s physiology and microhabitat use as it has expanded into higher elevations.

We first sought to determine if the coqui’s substrate use and baseline physiology differs between elevations. We found that frogs at high elevation were found closer to the forest floor and used different substrates than frogs from low and mid-elevations. This change in microhabitat use is likely in response to air temperature which tends to be warmer close to the ground at high elevation. We also found that two energy stores increased with elevation, likely to help coqui frogs cope with energetic demands of colder, less ideal temperatures. Taken together, our first study suggests the coqui’s microhabitat use and physiology does change in response to elevation.

Our second study concerned the thermal tolerance of the coqui frog in relation to elevation. We collected frogs from different elevations and tested their cold tolerance, glucose levels, and stress after three days in captivity to test for baseline elevational differences. We collected a second group of frogs and kept them in a cold- or warm-treatment for three weeks, after which we tested the same traits as above to assess the coqui’s acclimation ability according to elevation. Frogs from high elevations in the three-day group had greater cold tolerance than low elevation frogs. Cold-treated frogs in the three-week group had greater cold tolerance than warm-treated frogs. Glucose increased with elevation and was higher in cold-treated frogs after the three-week period, suggesting glucose is important for coping with cold temperatures. Finally, females had higher glucose and cellular damage than males in the three-day group. Our results indicate that coqui are more cold tolerant at high elevations, and can readily acclimate their thermal tolerance to cold temperatures, suggesting expansion into higher elevation habitats is possible.

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