For many terrestrial species, habitat associations and range size are dependent on
physiological limits, which in turn may influence large-scale patterns of species
diversity. The temperature range experienced by individuals is considered to shape
the breadth of the thermal niche, with species occupying temporally and/or geographically
stable climates tolerating a narrow temperature range. High-elevation environments
experience large temperature fluctuations, with frequent periods below 0 °C, but Grylloblatta
(Grylloblattodea: Grylloblattidae) occupy climatically stable microhabitats within
this region. Here we test critical thermal limits and supercooling points for five
Grylloblatta populations from across a large geographic area, to examine whether the
stable microhabitats of this group are associated with a narrow thermal niche and
assess their capacity to tolerate cold conditions. Thermal limits are highly conserved
in Grylloblatta, despite substantial genetic divergence among populations spanning
1500 m elevation and being separated by over 500 km. Further, Grylloblatta show exceptionally
narrow thermal limits compared to other insect taxa with little capacity to improve
cold tolerance via plasticity. In contrast, upper thermal limits were significantly
depressed by cold acclimation. Grylloblatta maintain coordinated movement until they
freeze, and they die upon freezing. Convergence of the critical thermal minima, supercooling
point and lower lethal limits point to adaptation to a cold but, importantly, constant
thermal environment. These physiological data provide an explanation for the high
endemism and patchy distribution of Grylloblatta, which relies on subterranean retreats
to accommodate narrow thermal limits. These retreats are currently buffered from temperature
fluctuations by snow cover, and a declining snowpack thus places Grylloblatta at risk
of exposure to temperatures beyond its tolerance capacity.