Date of Award

Spring 5-5-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Advisor

Danielle L Levesque

Second Committee Member

Kristina Cammen

Third Committee Member

José Meireles

Additional Committee Members

Andrew Rominger

Nishad Jayasundara

Abstract

Endothermy allows species to decouple body temperature from environmental
temperatures but does not equate to endothermic species maintaining those constant temperatures. Instead, heterothermy fluctuating body temperatures, both in and outside of torpor is common and allows endotherms to expand the limits of thermoneutrality. Thermolability is likely to be more common in the tropics and subtropics, where species live within or above their thermoneutral zone. My dissertation research focused on the heterothermic-homeothermic continuum, specifically quantifying where on the continuum different species fall at certain times and why those species have evolved to be at those points. I quantified the thermal profile of Sundamys muelleri, a tropical, nocturnal rodent. S. muelleri increased evaporative water loss and subcutaneous body temperature at ambient temperatures of 33°C, indicating an upper thermal limit, although metabolic rate showed no increase up to the highest ambient temperature (38.2°C), suggesting this species will tolerate future climatic changes. I then studied the extremely thermally-labile Tenrec ecaudatus. Although there was a wide range of intraindividual variability in metabolic rate and body temperature at both the higher and lower ambient temperatures, I identified a lower thermal limit thermoneutrality of 19.1°C. I then investigated how detailed climate variables may affect thermolability in Chiropteran species across biogeographical zones. I quantified how thermolability phenotypes in bats are globally distributed but found no relationship between thermoregulatory variables of body temperature and lower thermal limits and climatic variables. The unique thermoregulatory adaptations in Chiroptera gives us insights into the physiology and evolution of thermolability in endotherms. Finally, I focused on thermolability at the limits of thermoneutrality in Rodentia, the most diverse and specious clade of Mammalia. Body temperatures at the upper limits of thermoneutrality and the differential between the upper limit and the body temperature at that limit increase with latitude. However, the thermoneutral zone was wider for species with ranges at latitudes closer to the equator than the poles. Lower latitude species have lower temperatures at upper thermal limits and maintain their body temperatures closer to those limits. Through my research we can see how thermolability is shaped by evolutionary history, phylogeny, biogeographical patterns, and climate.

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