Oxygen limitation and thermal tolerance: a comparison of pulmonate and patellogastropod limpets
- Authors: Kankondi, Sebbi
- Date: 2017
- Subjects: Thermal tolerance (Physiology) , Limpets -- Physiology , Limpets -- Effect of temperature on , Oxygen consumption (Physiology)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7570 , vital:21274
- Description: Since the scientific community anticipates a general change in the global climate, it has become increasingly important to develop predictive models which encompass mechanisms to generate reliable forecasts of the effects this change on ecological communities and processes. To this end, the oxygen- and capacity- limited thermal tolerance (OCLTT) theory has been developed as a link between various physiological processes, the thermal aspect of climate change and the associated shifts at different levels of biological organization. This study set out to assess the general applicability of the OCLTT theory in eurythermal pulmonate and patellogastropod limpets, whose distributions overlap on the high shore rocks of the warm temperate, south-east coast of South Africa.This was done by determining their microhabitat use, median lethal temperatures and cardiac, Arrhenius breakpoint temperatures as measures of their upper thermal tolerance limits, in both air and water. The main hypotheses of the study were that the pulmonate limpets would be more common than the patellogastropods in warmer microhabitats during low tide and would have higher thermal limits than the patellogastropods in air and vice versa in water. This was based on the assumption that the two limpet groups have different capabilities of oxygen consumption in air and water, due to differences in their respiratory organs and that this would be reflected in their thermal tolerances based on predictions made by the OCLTT. This assumption was important because oxygen consumption was not measured in this study. Previous research (e.g. Garrity, 1984), showed that a thermal stress gradient exists among rocky intertidal microhabitats. From most to least thermally stressful the gradient is horizontal surfaces> slopes> vertical surfaces> tide pools> crevices. The current study found that, while the pulmonate limpets, Siphonaria capensis and S. serrata, preferred rock pools, sloped, vertical and horizontal rock surfaces, the patellogastropod limpets, Cellana capensis and Scutellastra granularis, preferred rock pools and vertical rock surfaces. Furthermore, the pulmonate limpets were only common on horizontal rock surfaces where specific ameliorating conditions would have mitigated thermal stress there. In addition, C. capensis had similar thermal tolerance limits to the pulmonate limpets in air and the pulmonate limpets had similar and/or higher thermal tolerance limits compared to S. granularis in water. This indicates that the pulmonate limpets did not necessarily prefer warmer microhabitats than the patellogastropod limpets and that there were no differences in the collective upper thermal tolerance limits between the two limpet groups in either medium.Consequently, there was no indication from this study that an assumed superior capacity for oxygen supply translates into greater thermal tolerance and that the hypotheses based on the OCLTT were not supported. Although this was an indirect test of the OCLTT theory, I conclude that this study does not support the notion of its general applicability and that mechanisms other than those outlined by the OCLTT theory may help explain the patterns of thermal limitation observed in the current study.
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- Date Issued: 2017
Metabolic energy relations in the Eastern Cape Angulate Tortoise (Chersina Anguluta)
- Authors: Setlalekgomo, Mpho Rinah
- Date: 2010
- Subjects: Eastern Cape angulate Tortoise , Oxygen consumption (Physiology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10690 , http://hdl.handle.net/10948/1400 , Eastern Cape angulate Tortoise , Oxygen consumption (Physiology)
- Description: The daily oxygen consumption (VO2) pattern, the effects of varying ambient temperatures, season and mass on the resting oxygen consumption (RVO2) of Chersina angulata of the Eastern Cape were investigated. The RVO2 was measured using flow-through respirometry and specific resting oxygen consumption (sRVO2) calculated. To determine the daily pattern in the VO2 of C. angulata, the tortoises were acclimated in an environmentally controlled room (ECR) to an ambient temperature of 26 ± 1°C and a light regime of 14 hours of light and 10 hours of darkness (14L:10D) for at least a week prior to the RVO2 measurements. The RVO2 was measured at a constant temperature of 26 ± 1°C, and at three different light regimes, namely: 14L:10D, constant darkness (DD) and constant light (LL). There were no significant effects of mass or gender on the sRVO2 of the tortoises used. Rhythms in the sRVO2 were detected under all three light regimes. The amplitudes of the rhythm were largest at 14L:10D, followed by DD and smallest at LL regime. The persistence of the rhythmic pattern under constant conditions suggests the existence of an endogenous circadian rhythm in the sRVO2 for adult C. angulata. To test for the effect of ambient temperature on the sRVO2 of adult C. angulata, the tortoises were acclimated to 22 ± 1°C and a 14L:10D light regime prior to the RVO2 measurements. RVO2 was measured at eight experimental temperatures; 14°C, 18°C, 22°C, 26°C, 30°C, 35°C, 38°C and 40°C. The sRVO2 was not influenced by gender and increased with experimental temperatures, but this did not happen consistently over the whole range of temperatures tested. A plateau, possibly a thermal preferendum zone, was detected within the temperature range of 26 - 38°C. Determination of seasonal effect on the sRVO2 of adult C. angulata was accomplished by acclimating tortoises to standard summer and winter conditions. Seasonal effects were tested in the appropriate seasons. Winter experiments were conducted in winter and summer experiments conducted in summer. The RVO2 was measured at experimental temperature 14°C, 18°C and 22°C. In addition RVO2 of iv winter-acclimated tortoises was also measured at 10°C. The sRVO2 increased significantly with increasing temperature within the temperature range tested. No distinct pattern was observed in the seasonal acclimation of adult C. angulata. The metabolic rate-temperature curves of the summer and the winter-acclimated tortoises cross each other. Season and temperature had no significant effects on the mass-scaling exponent of the sRVO2. The exponent ranged from 0.48 to 0.73 within the temperature range of 22 - 38°C. Below and above this temperature range, the exponent ranged from 1.47 to 1.67. An inverse relationship was observed between sRVO2 and body mass over the temperature range of 22 - 38°C. At 14°C and 18°C, sRVO2 increased with body mass, while at 10°C and at 40°C the slope was 1.01.
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- Date Issued: 2010