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The influence of thermal history on upper thermal limits of two species of riverine insects: the stonefly, Aphanicerca capensis, and the mayfly, Lestagella penicillata

Dallas, Helen F.
Hydrobiologia 2016 v.781 no.1 pp. 95-108
Diplopoda, Ephemeroptera, Plecoptera, heat tolerance, insects, rivers, spring, summer, water temperature, South Africa
The upper thermal limits of two cold-water stenotherms: the mayfly, Lestagella penicillata (Teloganodidae), and the stonefly, Aphanicerca capensis (Notonemouridae), were determined from six rivers in the Western Cape, South Africa. Limits were estimated using the Critical Thermal Method (expressed as Critical Thermal maximum) and the Incipient Lethal Temperature method (expressed as Incipient Lethal Upper Limit). Hourly water temperatures recorded in these rivers were used to characterise thermal signatures. Median CTₘₐₓ and 96 h ILUT varied significantly amongst rivers for both species (≤5.7°C for CTₘₐₓ and ≤4.0°C for 96 h ILUT) and variation was similar for both species. Differences in water temperature amongst rivers during the experimental period (spring) were insufficient (<2.0°C) to confirm the relationship between upper thermal limits and thermal history, expressed as an averaging statistic derived from in situ water temperatures. Greatest thermal range was over the warm summer period (>8.0°C) and it is likely that this is when thermal history may influence thermal limits. Maximum Weekly Allowable Temperature thresholds averaged for all rivers were lower for A. capensis (17.0°C) compared to L. penicillata (19.0°C). Both species have life cycles that allow them to avoid the thermally stressful summer period.