Thermal biology of aquatic insects in alpine lakes: Insights from diving beetles

Abstract

High mountain areas are especially vulnerable to global warming, as they ex-perience faster temperature changes than lowlands in a climate change con-text. Notably, increased temperatures and frequency of extreme flooding anddroughts, and the consequent decrease in ice cover and water availability fluctua-tions, will induce important physical changes in alpine freshwater systems. Thus,assessing thermal limits and exploring overwintering strategies of aquatic alpineinsects is pivotal to understanding how aquatic communities of high-mountainfresh waters will respond to climate change. However, knowledge on these topicsis still scarce for aquatic alpine insects.2. Here, the thermal biology of adults of five diving beetle species from alpinelakes located in the Sierra Nevada mountain range (southern Iberia) was stud-ied. Cold tolerance was measured estimating the supercooling point (SCP), lowerlethal temperature (LLT), tolerance to ice enclosure and to submersion, whereasheat tolerance was assessed from the heat coma temperature and upper lethaltemperature.3. All of the species survived ice enclosure for 3 h. Furthermore, three of the studiedspecies had SCPs higher than their LLTs, suggesting that they could be freeze-tolerant. All species except Agabus nevadensis also were tolerant to submersion,which could be a key adaptation for overwintering underwater below the icecover as adults, reducing risk from freezing conditions in the air. The species didnot differ significantly in their upper thermal limits, which were similar to those ofother dytiscids from lower altitudes.4. Overall, our results suggest that increasing temperatures is not expected to bethe most important threat for the water beetle populations in Sierra Nevada, butrather the colonisation of alpine lakes by lowland dytiscids in a warmer climatescenario.