Does ultraviolet radiation affect the thermoregulation and waking behaviour of the Eastern Dwarf Chameleon, Bradypodion ventrale?

Abstract

As ectotherms, reptiles bask in sunlight to regulate their body temperature. However, recent studies show that reptiles may be actively basking for ultraviolet light (UV) rather than temperature regulation. I aimed to assess whether UV influenced the thermoregulation and waking behaviour of the Eastern Dwarf Chameleon, Bradypodion ventrale. Three experiments were conducted in the laboratory: A UV-only gradient, an inversed gradient and a correlated gradient. The UV-only gradient was conducted to assess whether B. ventrale could actively regulate its UV exposure and whether females selected for higher UV exposures than male chameleons. The inversed and correlated gradients were conducted to assess whether B. ventrale was willing to lower and raise its body temperature below and above the species-specific preferred body temperature (Tpref), respectively, to maintain higher UV exposure. The experiments were conducted across all four seasons to account for any seasonal fluctuations in temperature and photoperiod. I found that B. ventrale can actively regulate its UV exposure and prioritised UV regulation over maintaining Tpref. However, chameleons were only willing to lower their body temperature below Tpref to maintain UV regulation and not willing to raise body temperatures above Tpref. Due to equipment limitations, it was unclear as to whether there was a difference in UV exposure preference between male and female chameleons. Once the influence of temperature was added, seasonal differences were found between the selected body temperatures of chameleons, suggesting that the physiology of B. ventrale is influenced by seasonal fluctuations in environmental temperature. Field observations were conducted to assess whether UV exposure, body temperature or predation pressure influenced the first movements of B. ventrale at sleep sites. Observations were made across all seasons to account for shifts in temperature and photoperiod. Chameleons were observed in the early mornings, from approximately 40 minutes before sunrise. When chameleons began shifting position or moving at their sleep site, the time of day, body temperature, ambient temperature and UVI were measured at the perch. I found that neither UV exposure, nor body temperature, nor predation influenced the first movements of B. ventrale. However, observations indicated that light may strongly influence the waking behaviour of B. ventrale, although this is still to be adequately assessed. Bradypodion ventrale were willing to raise body temperatures above Tpref for only short periods, meaning they could benefit from increasing environmental temperatures as they may not have to bask as long for thermoregulation and vitamin D3 synthesis. The influence of UV exposure on thermoregulation in the laboratory is not easily translated into nature as there may be other factors influencing thermoregulatory behaviour. Thus, future studies should consider conducting more field ii studies regarding UV exposure in this species to assess the influence of UV on temperature regulation properly. It is also suggested that future studies consider the influence of light on the waking behaviour of B. ventrale, specifically light from urban areas at night. This study provides the first record of active regulation of UV exposure in a dwarf chameleon from the Bradypodion genus, gives insight into how thermoregulation is affected by the presence of UV, and vice versa, in a laboratory setting and contributes to the growing field of research on the importance of UV exposure in reptiles.Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 202