Award Date

5-15-2026

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Life Sciences

First Committee Member

Frank van Breukelen

Second Committee Member

Jef Jaeger

Third Committee Member

Sean Neiswenter

Fourth Committee Member

Allyson Hindle

Fifth Committee Member

Haroon Stephen

Number of Pages

126

Abstract

The relict leopard frog (Rana onca) once ranged across drainages in southern Nevada, northwestern Arizona, and southwestern Utah. Following a decline, the species only persisted in a few geothermally influenced hot springs, which led to the perspective that hot springs were high-quality habitat. Rana onca has been under intensive, multiagency management and the species has been translocated to establish additional populations, including at cold-water sites. Three research studies are presented into the thermal physiological ecology of R. onca with the aim of informing conservation strategy. The research was focused at a thermally influenced hot spring and a cold-water spring to allow for comparisons between these temperature regimes.

The first study (Chapter II) evaluates the thermal ecology of adult R. onca by continuously monitoring body temperature in the wild across nearly two years. Temperature preference of adult frogs was assessed in the laboratory. Frogs did not differ in temperature preference between the sites or seasons. Despite these results, the thermal profiles of frogs in the field at the hot site were 2.5°C higher in winter and 5.7°C higher in summer then frogs at the cold site. In summer, frogs at the hot site appeared to seek the lowest possible temperatures available to them, although these frogs were unable to reach lower temperatures preferred in the laboratory. Frogs at the cold site, in comparison, were able to maintain cooler, preferred temperatures. In winter, frogs used two strategies when overwintering, active and relatively inactive, identified through variability and differences in body temperatures. Frogs with low variability in body temperatures (inactive frogs) appeared to thermally conform to cold-waters at both the hot and cold sites through most of winter. Other frogs remained active and feeding in many cases.

In the second study (Chapter III), oxygen consumption rate (VO2) of adult frogs was measured at ecologically relevant temperatures as a proxy for energy demand. The VO2 data were used to develop temperature coefficients that allowed extrapolations of values to the body temperatures from the field data collected in the first study. The models were then used to quantify differences in seasonal energy demands of frogs between the hot and cold sites. Winter feeding and adult seasonal body condition were also evaluated. The frogs at the hot site had energy demands that were 1.14-fold higher in winter and 1.27-fold higher in summer compared to those at the cold site. Frogs at both sites were found to feed during winter, with no difference in the mass of prey consumed between sites. Frogs at the hot site were smaller in size with significantly lower body conditions than those at the cold site. This difference provides support for the perspective that the hot site required higher energy investment in physiological maintenance at the expense of energy for reserves, growth, and likely reproduction.

The third study (Chapter IV) provides research into the thermal physiological ecology of early life stages. Water temperatures of breeding pools were monitored when egg masses and tadpoles were present. Energy demands were then modeled using these water temperatures and VO2 of individual eggs and tadpoles measured in the laboratory. Modeled energy demands showed differences of 1.30 to 2.72-fold higher for eggs in the warm pools then the cold pools. The values for tadpoles were 1.45 to 2.43-fold higher. Field observations suggest that R. onca tadpoles may no longer be able to reach metamorphosis from the warmest pool.

Information from these studies can be used by managers of R. onca to evaluate the overall thermal quality and quantity of habitat at hot springs. The findings can also inform on target temperatures when expanding or creating microhabitats at important hot spring sites, thus providing favorable energetic conditions for development, growth, and survival of R. onca. The findings also inform on the scale of potential impacts to R. onca populations from predicted regional temperature increase due to climate change.

Keywords

Body temperature; energy demands; hot spring; overwintering; Rana onca; thermoregulation

Disciplines

Biology | Environmental Sciences | Medical Physiology | Physiology | Terrestrial and Aquatic Ecology

File Format

PDF

File Size

1693 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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