Doctoral Degrees (Botany and Zoology)

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Browsing Doctoral Degrees (Botany and Zoology) by Subject "Agama -- Ecology"

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    Thermal physiology, behaviour and fitness in the lizard Agama atra: exploring inter-individual variation in the context of environmental change
    (Stellenbosch : Stellenbosch University, 2020-03) Alujevic, Karla; Clusella-Trullas, Susana; Logan, Michael; Streicher, Jeffrey; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Individuality in a wide range of fitness-related traits has been well documented in both vertebrates and invertebrates. Examining variation in ecologically relevant traits, and the functional integration of these traits, is a crucial step in understanding the evolution of complex phenotypes in nature. With selection acting on individual phenotypic variation, understanding the links between fitness related traits and their temperature dependence should provide insight into the maintenance of different ‘life-strategy’ phenotypes in different natural contexts. This thesis investigated intra-population variation in thermal dependence of physiological and behavioural traits as well as the linkages between intra-population phenotypic variation and microclimate in the southern rock agama lizard (Agama atra). Selection simultaneously acts upon suites of traits that interact to form multivariate phenotypes. Nevertheless, individual measures of performance are often examined in isolation. To identify patterns of inter-individual variation within and across traits, I examined patterns of variation in the thermal sensitivity of ecologically important physiological and performance traits (resting metabolic rate, water loss rate, sprint speed, running endurance and bite-force), in southern rock agamas. Results suggest that physiological and performance traits appear to exist as a complex phenotype and provide first evidence for the presence of correlations between individual thermal sensitivities of physiological and performance traits. Next, I investigated if behavioural traits are grouped within personality types in A. atra. The integration between thermal performance and personality has recently been incorporated within the thermal-behavioural syndrome (TBS) with the premise that thermal physiology drives individual behaviour. To test this hypothesis, I explored the relationship between behavioural traits (personality) and thermal performance, following the prediction of TBS. While the presence of both ‘behavioural types’ and ‘thermal types’ was found, the direction of correlations within TBS was mediated by body mass. The most comprehensive paradigm explaining the prevalence of animal personality is the pace- of-life-syndrome (POLS). Mixed support for the integration of traits within POLS in ectotherms could be attributed to the effect of abiotic factors that have the potential to mediate the relationship between physiological, performance and behavioural traits. To address this, I tested the effect of temperature on the covariation between physiology, performance and personality (i.e. POLS). Despite theoretical predictions, (thermal sensitivity of) resting metabolic rate did not drive variation in sprint speed and personality in the southern rock agama. However, thermal plasticity of boldness covaried with sprint speed plasticity in large males. Behavioural strategies are the primary mechanism by which many ectothermic species cope with the temperature change in their environments. Animals occupying territories with high frequencies of favourable thermal microclimates should incur lower thermoregulatory costs, and therefore, be able to invest more time into other important ecological tasks. To test these predictions, I investigated how thermal quality (estimated as the overlap between individual optimal thermal performance range and available operative temperatures within respective territories) affects accuracy of thermoregulation and behaviour of males in the study population. Results of this field study show that thermal quality of individual territories drives variation in body temperature, accuracy of thermoregulation and signalling behaviour of males in a population of southern rock agama lizards. An outstanding question of this research is how the interplay between thermal properties of territories, thermal performance characteristics and individual personality may shape the fitness of these lizards. To understand the mechanisms that shape organism fitness, this project aimed to estimate reproductive success of A. atra lizards using ddRAD sequencing and pedigree analyses, and link these results to individual thermal and behavioural ecology. While this approach offered various analytical challenges that require further research, preliminary analyses suggest the presence of substantial genetic variation and SNP heterozygosity in the study population. In addition, observed differences in mean pairwise genetic distances are consistent with physiological and performance traits being heritable. The results of these analyses thus far are encouraging for linking inter-individual variation in thermal physiology, performance, behaviour and territory thermal quality to individual reproductive output. This holistic approach will aid in understanding the mechanisms underlying lizard fitness but also how selection might drive adaptive evolution of thermal traits of ectotherms in the context of environmental change.