How aquatic insects cope with cold temperatures is poorly understood. This is particularly true for high-elevation species, which often experience a seasonal risk of freezing. In the Rocky Mountains, nemourid stoneflies (Plecoptera: Nemouridae) are a major component of mountain stream biodiversity and are typically found in streams fed by glaciers and snowfields, which are rapidly receding due to climate change. Predicting the effects of climate change on mountain stoneflies is difficult because their thermal physiology is largely unknown. We investigated cold tolerance of several alpine stoneflies (Lednia tumana, Lednia tetonica, and Zapada spp.) from the Rocky Mountains, USA. We measured the supercooling point (SCP) and tolerance to ice enclosure of late-instar nymphs collected from a range of thermal regimes. SCPs varied among species and populations, with the lowest SCP measured for nymphs from an alpine pond, which was much more likely to freeze solid in winter than flowing streams. We also show that L. tumana cannot survive being enclosed in ice, even for short periods of time (h) at relatively mild temperatures (-0.5°C). Our results indicate that high-elevation stoneflies at greater risk of freezing may have correspondingly lower SCPs, and despite their common association with glacial meltwater, these stoneflies appear to be living near their lower thermal limits.



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© 2021 Brigham Young University

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Western North American Naturalist

Supplementary Material 1.pdf (2231 kB)
Two size classes of Lednia tumana present in a quantitative September 60 WESTERN NORTH AMERICAN NATURALIST (2021), VOL. 81 NO. 1, PAGES 54–62 sample of the macroinvertebrate community from Lunch Creek, Montana, USA.

Supplementary Material 2.pdf (245 kB)
Daily mean temperatures for the 3 streams included in this study with a complete year of temperature data. Wind Cave and Skillet Glacier data are from 2016 to 2017. Lunch Creek was measured in 2013–2014.

Supplementary Material 3.pdf (21 kB)
Additional details about the populations used in this study (e.g., latitude and longitude) as well as experimental conditions (e.g., holding period, sample size).

Supplementary Material 4.pdf (2439 kB)
Stonefly nymph length versus supercooling point (SCP) and boxplots of body length by species.

Supplementary Material 5.pdf (16 kB)
Tukey-adjusted differences in supercooling point (SCP) for pairs of populations.