Thermal adaptation in the lizard Cordylus oelofseni : physiological and behavioural responses to temperature variation

Basson, Christine Helene (2013-12)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: As ectotherms, lizards are particularly vulnerable to changes in the thermal landscape and face extinction risk if they lack the capacity to rapidly adapt or behaviourally mitigate increasingly altered thermal environments. Theoretical models that predict lizards‟ response to climate change often fail to take into account the thermal characteristics of the microenvironment, the ability of lizards to behaviourally buffer climate variation in the habitat and the plastic nature of both behaviour and physiology over ecologically relevant time-scales. Here, I address this major knowledge gap using two separate research chapters in an experimental physiology approach. In Chapter 1, I investigated the temperature-dependence and plasticity of resting metabolic rate, water-loss rate and preferred body temperature of Cordylus oelofseni at several temporal scales (within and between seasons) and incorporated field observations to acquire a better understanding of this species‟ adaptive potential to buffer thermal changes in the habitat. Cordylus oelofseni showed plasticity of both behaviour and physiology in response to thermal acclimation, but relied on distinct strategies depending on the time-scale investigated. These results highlighted the complexity of underlying mechanisms used by these organisms to buffer temperature variation. In Chapter 2, I used an experimental approach to examine the energetic costs of thermoregulation in C. oelofseni and test the cost-benefit model of thermoregulation. This model‟s primary prediction states that lizards should thermoregulate carefully only when the associated costs are low. Using four enclosures that simulated different thermal qualities (temporal and spatial distributions of operative temperatures) in the habitat, I found limited support for the cost-benefit model. Lizards in the low-quality heterogeneous enclosures invested the same energetic effort and thermoregulated with similar overall accuracy as lizards in the high-quality heterogeneous enclosure. The costs incurred were not necessarily energetic, but reflected missed opportunities (e.g. less time to forage), something that, along with important interaction effects with body mass, deserves further attention when testing this model. Together, these results illustrate the importance of incorporating ecological reality at various time and spatial scales in order to make relevant predictions regarding the fate of lizards with projected climate change.

AFRIKAANSE OPSOMMING: As ektotermiese diere, is akkedisse veral sensitief vir veranderinge in die termiese landskap en staar uitsterwingsrisiko in die gesig as hulle nie die vermoë het om vinnig aan te pas of gedragsveranderinge te maak in omgewings wat toenemend verwarm nie. Teoretiese modelle wat akkedisse se reaksie op klimaatsverandering voorspel, neem dikwels nie die termiese eienskappe van die mikro-omgewing, die vermoë van akkedisse om met gedragsveranderinge klimaat variasie in die habitat te buffer en die plastieke aard van beide gedrag en fisiologie oor ekologies relevante tydskale in ag nie. Hier bespreek ek hierdie groot kennisgaping met behulp van twee afsonderlike navorsingshoofstukke in 'n eksperimentele fisiologie benadering. In Hoofstuk 1 het ek ondersoek ingestel na die temperatuur-afhanklikheid en plastisiteit van rustende metaboliese tempo, waterverlies tempo en voorkeur liggaamstemperatuur van Cordylus oelofseni by verskeie tydskale (binne en tussen seisoene) en inkorporeer veld waarnemings om 'n beter begrip te verkry van hierdie spesie se aanpasbare potensiaal om termiese veranderinge in die habitat te buffer. Cordylus oelofseni het plastisiteit van beide gedrag en fisiologie in reaksie op hitte-akklimatisering getoon, maar staatgemaak op verskillende strategieë, afhangende van die tyd-skaal wat ondersoek is. Hierdie resultate beklemtoon die kompleksiteit van die onderliggende meganismes wat gebruik word deur hierdie organisme om temperatuur verandering te buffer. In Hoofstuk 2 het ek 'n eksperimentele benadering gebruik om die energiekoste van termoregulering in C. oelofseni te ondersoek en die kostevoordeel model van termoregulering te toets. Hierdie model se primêre voorspelling verklaar dat akkedisse slegs versigtig moet termoreguleer wanneer die gepaardgaande koste laag is. Deur gebruik te maak van vier afskortings wat verskillende termiese eienskappe gesimuleer het (tyd en ruimtelike verspreiding van operatiewe temperature) in die habitat, het ek beperkte ondersteuning gevind vir die koste-voordeel model. Akkedisse in die lae-gehalte heterogene afskortings het dieselfde energieke moeite belê en getermoreguleer met soortgelyke algehele akkuraatheid as akkedisse in die hoë-gehalte heterogene kamp. Die kostes wat aangegaan is, is nie noodwendig energiek nie, maar weerspieël geleenthede wat gemis is (bv. minder tyd om kos te soek), iets wat, saam met belangrike interaksie effekte met liggaamsmassa, verdere aandag verdien wanneer hierdie model getoets word. Tesame illustreer hierdie resultate die belangrikheid van die integrasie van ekologiese werklikheid op verskillende tyd en ruimtelike skale, om relevante voorspellings oor die lot van akkedisse met geprojekteerde klimaatsverandering te kan maak.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95471
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