Temperature responses vary between riffle beetles from contrasting aquatic environments

Area of Science:

• Ecology
• Environmental Science
• Aquatic Biology

Background:

• Organisms in stable ecosystems are predicted to have narrow environmental tolerances.
• Previous studies on invertebrates in spring habitats have yielded inconclusive results regarding this prediction.
• Riffle beetles (family: Elmidae) are common in various aquatic environments.

Purpose of the Study:

• To investigate the effects of elevated temperatures on four species of riffle beetles native to Texas.
• To compare the thermal tolerance profiles of spring-associated species with more cosmopolitan surface stream species.
• To determine if spring-associated species exhibit stenothermal (narrow temperature tolerance) profiles.

Main Methods:

• Dynamic and static assays were used to assess the performance and survival of four elmid species under increasing temperatures.
• Metabolic rates of the four species were measured in response to thermal stress.
• Species included two spring-associated (Heterelmis comalensis, Heterelmis cf. glabra) and two surface stream species (Heterelmis vulnerata, Microcylloepus pusillus).

Main Results:

• Heterelmis comalensis, a spring-associated species, was found to be the most sensitive to thermal stress.
• Microcylloepus pusillus, a cosmopolitan surface stream species, demonstrated the least sensitivity to thermal stress.
• While both spring-associated species showed increased metabolic rates with rising temperatures, Heterelmis comalensis exhibited a narrower thermal tolerance than Heterelmis cf. glabra.

Conclusions:

• The results support the hypothesis that spring-associated riffle beetles have stenothermal tolerance profiles.
• Species inhabiting stable spring ecosystems (H. comalensis, H. cf. glabra) are more sensitive to thermal stress than widespread surface stream species (M. pusillus).
• Variations in thermal tolerance among spring specialists may be influenced by local climatic and hydrological conditions.