DOI: 10.5061/dryad.m63xsj49q
title: Acclimation to moderate temperatures can have strong negative impacts on heat tolerance of arctic arthropods

description: The Arctic is impacted by some of the fastest temperature changes observed
 on Earth, but the impact on terrestrial arthropod fauna is unclear. Acute
 physiological thermal limits of terrestrial ectotherms from high latitudes
 often exceed the local air temperatures, suggesting that they may be able
 to cope with increasing temperatures. However, knowledge of how arctic
 terrestrial arthropods cope with elevated temperatures for longer periods
 is lacking. Here we investigate how acclimation temperature and exposure
 time affect the acute physiological heat tolerance of five terrestrial
 arthropod species (Neomolgus littoralis, Megaphorura arctica, Nysius
 groenlandicus, Psammotettix lividellus, and Nabis flavomarginatus)
 immediately after collection in arctic and sub-arctic
 habitats. We show that although acute heat tolerances are
 relatively high, even exposure to moderate (temperature span assessed ca.
 3-29°C) acclimation temperatures for 24 hours have strong negative effects
 on heat tolerance for four of the five species. Similarly, exposure time
 negatively affected heat tolerance, depending on species and temperature.
 Together our results suggest that exposure to even moderately elevated
 temperatures for periods of 24 h or even shorter can lead to lower acute
 heat tolerance for cold-adapted terrestrial arthropod species from
 sub-Arctic and Arctic regions. Consequently, climate change leading to
 extended periods of mildly elevated temperatures may have strong negative
 effects on these species. We argue that this aspect is currently
 overlooked when assessing the ability of arthropods from Arctic and
 sub-Artic regions to cope with climate changes as such predictions are
 typically based on acute heat tolerance estimates and with the assumption
 of beneficial acclimation responses.
description: <strong><em>Microhabitat
 temperatures</em></strong> Temperature
 loggers were placed at the sites where the animals were collected. At Ny
 Ålesund, two SmartButton loggers (SmartButton, ACR System Inc.) were
 placed in and on gravel at the beach to record the thermal environment
 (every 5 minutes) where individuals of <em>N. littoralis</em>
 were caught, and at a protected and an exposed tundra area,
 representative. At Narsarsuaq, air temperature and ground-level
 temperature at the collection site were continuously recorded (every 15
 minutes) using TMS-4 dataloggers (TMS-4, TOMST, Czech Republic) to record
 the thermal environment in which the individuals were caught.
 <strong><em>Thermal
 tolerance</em></strong> Two assays were
 used to measure heat tolerance in the present study: 1) critical thermal
 maximum temperature (CTmax), where the specimens were exposed to gradually
 increasing temperatures and the temperature at which they entered heat
 coma was recorded, and 2) heat knockdown time (HKDT), where the specimens
 were exposed to a constant, stressful temperature, and the time until heat
 coma was recorded. <em>Thermal maximum
 temperature (CTmax)</em> CTmax was established
 for the Svalbard species (<em>N. littoralis</em> and
 <em>M. arctica</em>) using Elara 3.0 (IoTherm, Laramie, WY), a
 portable fully programmable heating/cooling anodized aluminum stage
 designed to maintain precision temperatures (Oyen et al., 2016).
 Individuals were individually placed in a 24-well plate drilled in 5mm
 acryl (each well had a diameter of 15 mm), with a bottom made of 1mm
 aluminum, and a lid made of 5mm acryl. The plate was subsequently placed
 on a thermoelectric plate of Elara 3.0. The plate was insulated from room
 air within a polystyrene box (16 (W)X 18.5 (L) X 19 (H) cm and 2.5 cm
 thick). Using a metal frame, a camera with an 8mm lens (Basler USB 3.0)
 (Basler Inc, Exton, PA) was mounted on top of the cooler allowing
 recording of the behaviour of animals during thermal exposure using the
 Basler camera Pylon Viewer (version 5.1.0.12681) software. The individuals
 were exposed to the following temperature profile: 10 min at 10°C and
 subsequently the temperature was increased by 0.2 ± 0.01°C
 min<sup>−1</sup>. Heat tolerance estimates were based on
 manual observations of behaviour using video recordings and the time of
 the last movement was assumed to constitute their CTmax. During each run,
 a temperature logger (SmartButton, ACR System Inc.) was placed on the
 thermoelectric plate of the Elara 3.0 and used to calculate
 CTmax. <em>Heat knockdown time
 (HKDT)</em> For the Greenlandic species
 (<em>N. groenlandicus</em>, <em>N.
 flavomarginatus</em>, and <em>P. lividellus</em>), 5 ml
 vials containing field-collected individuals were mounted to a rack and
 submerged into a temperature-controlled water bath (PolyScience MX
 Immersion Circulator: MX-CA12E) maintained at 48.3°C for <em>N.
 groenlandicus</em>, at 44.4°C for <em>N.
 flavomarginatus</em>, and at 46.1°C for <em>P.
 lividellus</em>. The individuals were then observed and stimulated
 with flashes of light and gentle tapping on the vial caps with a metal
 rod. The time until movement ceased was recorded for each individual. We
 used heat knockdown temperatures that resulted in HKDT lower than 60
 minutes for each species. For Svalbard species
 (<em>N. littoralis</em> and <em>M. arctica</em>),
 HKDT was obtained using Elara 3.0 (IoTherm, Laramie, WY), where
 <em>N. littoralis</em> was exposed to a constant temperature
 of 40.5°C and <em>M. arctica</em> at 30.0°C. The heat
 tolerance estimates were based on manual observations of behaviour using
 video recordings and the time of the last movement to constitute their
 HKDT. During each run, a SmartButton temperature logger (SmartButton, ACR
 System Inc.) was placed on the thermoelectric plate of the Elara 3.0 to
 establish realised heat knockdown temperatures.
description: # Acclimation to moderate temperatures can have strong negative impacts on
 heat tolerance of arctic arthropods
 [https://doi.org/10.5061/dryad.m63xsj49q](https://doi.org/10.5061/dryad.m63xsj49q) ## Description of the data and file structure The data consists of an Excel file with the following sheets: 1\) Readme (sheet 1). 2\) Heat tolerance data (sheet 2; Svalbard CTmax): Critical thermal maximum temperature (CTmax; °C), where the specimens were exposed to gradually increasing temperatures, and the temperature at which they entered heat coma was recorded. Two species from Svalbard (*Neomolgus littoralis, Megaphorura arctica).* 3\) Heat tolerance data (sheet 3-4; Acclimation Svalbard and Greenland): The effect of moderate acclimation temperatures (°C) and exposure times on upper thermal limits (HKDT: heat knockdown time; minutes) of five arctic arthropods: *Neomolgus littoralis, Megaphorura arctica, Nysius groenlandicus*, *Psammotettix lividellus*, and *Nabis flavomarginatus* immediately after collection in the Arctic (Svalbard) and sub-Arctic (Southern Greenland). 4\) Microhabitat temperatures (sheets 5-6; Microhabitat temp Svalbard and Greenland): Temperature loggers were placed at the sites where the animals were collected. At Ny Ålesund, two SmartButton loggers (SmartButton, ACR System Inc.) were placed in and on gravel at the beach to record the thermal environment (every 5 minutes) where individuals of *N. littoralis* were caught, and at a protected and an exposed tundra area, representative. At Narsarsuaq, air temperature and ground level temperature at the collection site were continuously recorded (every 15 minutes) using TMS-4 dataloggers (TMS-4, TOMST, Czech Republic) to record the thermal environment in which the individuals were caught.