Award Date

1-1-2007

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Committee Member

Frank van Breukelen

Number of Pages

78

Abstract

Compared with other terrestrial vertebrates, amphibians are generally less tolerant of thermal extremes. The Mojave Desert has ambient temperatures outside the proposed thermal tolerance zone of its mort abundant amphibian, the Red-spotted toad (Bufo (Anaxyrus) punctatus). Few data have been presented regarding the thermal ecology of these animals, including their thermal histories and proposed strategies to avoid temperature extremes. Previous studies suggest B. punctatus avoids extreme thermal exposure and adult toads experience body temperature (Tb) below a proposed critical thermal maximum (CTmax) of 35°C, and can maintain Tb at 25°C during the winter. Further, previous studies indicate a CTmax for tadpoles of 33°C. A reassessment of the thermal ecology of Red-spotted toads was warranted based on personal observations reported in this thesis; I recorded environmental and/or Tb of Red-spotted toads across their entire life history: eggs, tadpoles, juveniles and adults. In the field, eggs and tadpoles may encounter water temperatures as high as ~40°C. Juveniles can experience Tb as high as 42.2°C. Adult toads experience Tb as high as 39.1°C. These observations were combined with experimental determination of CTmax across life history statges: the CTmax of tadpoles was variable, but decreased as development progressed; adult toads exhibit a CTmax as high as 45.2 +/- 1.0°C. I documented thermal preferences (Tp) of tadpoles and adults. In contrast to other studies of the effect of ontogeny on preferred temperature, Tp, of Red-spotted toads remains fairly constant across development. I documented developmental time from egg deposition to metamorphosis at 18 days in the summer and 47 days in the spring---both periods are less than the previously described 60-day developmental period. Finally, I present preliminary data on apparent basking-like behavior of late stage tadpoles in the field; Despite seemingly high and presumably stressful environmental temperatures, Red-spotted toads do not generally live on the verge of thermal tolerance. However, later stage tadpoles may encounter potentially lethal temperatures. The collected data document the thermal ecology of Red-spotted toads and contradict previously assumed limits that may not have been experimentally-derived. These data may allow informed decision making in land use and conservation efforts by better defining an important ecological parameter in a species that may be subjected to increased pressures by human activity and climatic change.

Keywords

Bufo; Ecology; History; Life; Punctatus; Red; Spotted; Thermal; Toad

Controlled Subject

Ecology; Physiology

File Format

pdf

File Size

2201.6 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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