Abstract
Freshwater environments are known to support highly diverse ecosystems and provide fundamental resources for the survival of humans, such as water for drinking, farming, and irrigation. Despite the obvious importance of freshwater resources for both humans and aquatic ecosystems, they are severely threatened by anthropogenic activities and are vulnerable to climate change. Climate change is expected to cause an increase in river temperatures and variability in weather patterns, resulting in increased temperature fluctuation in aquatic systems. Aquatic organisms have an optimal temperature range for metabolic functioning which, depending on the taxon, may be narrow (stenothermal) or wide (eurythermal). Research into the thermal tolerance of aquatic organisms, particularly invertebrates, is gaining ground internationally, but in the Southern Hemisphere the field is still in its infancy, particularly so for southern Africa. To help rectify the knowledge gap, this study aims to, firstly, establish baseline information on the thermal tolerance of a widespread eurythermal mayfly, Baetis harrisoni Barnard, secondly, to assess the influence of thermal history on thermal tolerance for various populations of this species, thirdly, to determine seasonal variation in thermal tolerance within populations, fourthly, to compare thermal resilience among male and female individuals and fifthly, to determine whether thermal tolerance is related to body size. To achieve these aims, B. harrisoni individuals were collected from various streams around the Gauteng province of South Africa during different seasons of the year. In the laboratory, collected individuals were subjected to either the Critical Thermal Maximum (CTM) or Incipient Lethal Temperature (LT50) technique to assess acute and chronic responses to thermal stress, respectively. Most of the data from the LT50 experiments supported the hypothesis that thermal history (background median stream temperature) is positively related to thermal tolerance, but this was not the case for the CTM experiments, which yielded inconsistent results in this regard...
M.Sc. (Zoology)