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Thermal biology of the spotted snow skink, Niveoscincus ocellatus, in a warming world

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Yuni, LP (2016) Thermal biology of the spotted snow skink, Niveoscincus ocellatus, in a warming world. PhD thesis, University of Tasmania.

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Abstract

Thermal environment vary geographically and over time and they can have direct and
indirect effects on natural populations, especially in ectotherms. Ectotherms rely on their
thermal environment for thermoregulation, and the body temperatures they are able to
maintain affect their physiological processes such as locomotor performance,
developmental and growth rates, and energy expenditure. This thesis focusses on the
thermal flexibility of a widely distributed ectothermic species, the spotted snow skink
(Niveoscincus ocellatus) along an altitudinal gradient and across seasons to understand
population-specific responses to different environmental conditions which may be
important in allowing the species to occupy divergent thermal habitats. Further, I use this
as a base to predict some of the potential effects of future climate change on this species
(and ectotherms more generally).
I began by investigating the thermal biology (field active body temperature and
thermal preference in the laboratory) across seasons in three populations of the spotted
snow skink, Niveoscincus ocellatus, living along an altitudinal gradient in Tasmania. I
demonstrated that the field active body temperature of N. ocellatus is dependent on its
thermal environment but that the thermoregulation strategy might vary among populations
of this species to respond to the variation in thermal environments at their localities. After
establishing their thermal preferences in the laboratory that did not vary with site or
season, I showed that N. ocellatus met their thermal preference along the altitudinal
gradient and in all seasons, with an exception for the high altitude population in autumn.
Their ability to meet their preferred body temperatures despite geographic and seasonal
variation in thermal opportunities is important in allowing them to inhabit a wide range
distribution area.
Since the field active body temperature in N. ocellatus depended on their thermal
environments, I then focussed on other key physiological traits, namely on locomotor
performance, energy expenditure, and date of birth that might be affected by the variation
in the field active body temperatures in this species. I focused on the altitudinal and
seasonal variation in the relationship between locomotor performance (sprint speed and
endurance) and temperature in this species with particular focus on thermal optimum (Topt)
and performance breadth (B80). Geographic variation was found in locomotor performance
of N. ocellatus. The high altitude population had lower thermal optimum (Topt) and a wider
performance breadth (B80) due to a lower limit of B80 than populations at the lower altitudes. The higher limit of B80, however, remained consistent among populations. These
shifts toward lower Topt and lower limit of B80 reflect the conditions they experience at the
high altitude compared to the lower altitude sites. This reflects divergence in temperatures
at which they are likely to be active at the lower sites when they emerge and prior to
reaching their optimal temperatures. In contrast, higher temperatures can easily be avoided
through thermoregulation and thus selection acts less strongly on this trait. There was also
evidence of a seasonal shift in the relationship between temperature and locomotor
performance which suggests a capacity for plastic responses in these traits – however this
was only evident for B80 of endurance. However, the strong site effect and the absence of
widespread seasonal signals suggest local adaptation to local climatic conditions.

Item Type: Thesis (PhD)
Keywords: Thermal flexibility, temperature, lizards, Niveoscincus, locomotor performance, energy expenditure, date of birth, thermoregulation
Copyright Information:

Copyright 2016 The Author

Date Deposited: 26 Oct 2016 03:52
Last Modified: 26 Oct 2016 03:52
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