Date of Award

January 2013

Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Paul V. Cupp

Department Affiliation

Biological Sciences

Abstract

The Critical Thermal Maxima (CTMax) is a measure of upper thermal tolerance. The physiological response upon reaching CTMax is similar across taxa, making CTMax useful in comparative studies. The CTMax defines the ecological lethal temperature of an organism and has been used to predict the effects of global climate change. CTMax was determined for adults and first instar nymphs of three species of tropical cockroaches: Blaptica dubia, Eublaberus posticus, and Blaberus discoidalis. Adult cockroaches were acclimated to temperatures of 10°C, 15°C, 20°C, 25°C, 31°C and 37°C for a period of seven days. Blaptica dubia was the only species to survive the acclimation period at temperatures of 10°C and 37°C. All three species survived at 15°C, 20°C, 25°C and 31°C and at each temperature there were significant differences in CTMax between two or more species. The average CTMax values at 25°C were significantly different between all species, Blaptica dubia (47.82°C ± 0.53°C), Eublaberus posticus (45.57°C ± 0.42°C) and Blaberus discoidalis (44.49°C ± 0.44°C).

Across acclimation temperatures, the response of the CTMax varied within each species. Blaptica dubia exhibited a significantly higher CTMax value at 37°C than all other acclimation temperatures (49.18°C ±0.80°C) and Eublaberus posticus had significantly higher CTMax values at 15°C (46.89°C ± 0.35°C) and 31°C (47.27°C ± 0.64°C). Blaberus discoidalis did not exhibit any significant changes in CTMax at any acclimation temperature.

First instar nymphs of each species were acclimated at 25°C. Eublaberus posticus nymphs (44.77°C ± 1.01°C) had significantly different CTMax values than adults. No significant differences in CTMax were detected between first instar nymphs and adults in Blaptica dubia and Blaberus discoidalis.

The rate of the acclimation response was tested in Blaptica dubia for roaches acclimated at 10°C for a period of seven days then exposed to 37°C. The reverse response was also tested. CTMax values significantly increased when cockroaches acclimated to 10°C (47.06°C ± 0.63°C) were exposed to 37°C for a period of six hours (49.18°C ± 1.13°C), after 96 hours (48.38°C ± 0.79°C) CTMax values returned to those at 10°C. Animals acclimated at 37°C and moved to 10°C showed no changes in CTMax values.

The findings of this study suggest that tropical cockroaches are limited in their ability to shift their upper thermal tolerance when exposed to novel acclimation temperatures. The CTMax values determined in this study are consistent with previous studies of cockroach CTMax and can be applied to future modeling of the effects of climate change.

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