Landscape effects on the thermotolerance of carabid beetles and the role of behavioral thermoregulation

Abstract

Physiological thermotolerance and behavioral thermoregulation are central to seasonal cold adaptation in ectothermic organisms. For species with enhanced mobility, behavioral responses may be of greater importance in the cold stress response. Employing the carabid beetles as a study organism, the current study compared physiological thermotolerance and behavioral thermoregulation in carabid species inhabiting cereal fields in different landscape contexts, from fine grain heterogeneous "complex" landscapes to homogenous "simple" landscapes. Physiological thermotolerance was determined via measurement of the CT_min and chill coma temperature. Behavioral responses to cold temperature exposure were determined employing a purpose built arena, and thoracic temperature measured to estimate the efficacy of the behavior as a form of behavioral thermoregulation. Results revealed an influence of landscape composition on the cold tolerance of carabid beetles, although species differed in their sensitivity to landscape intensification. A reduced effect of landscape on the thermotolerance of larger carabid beetles was observed, thought to be the consequence of greater mobility preventing local acclimation to microclimatic variation along the landscape intensification gradient. Investigation into behavioral thermoregulation of the 3 largest species revealed burrowing behavior to be the main behavioral response to cold stress, acting to significantly raise carabid body temperature. This finding highlights the importance of behavioral thermoregulation as a strategy to evade cold stress. The use of behavioral thermoregulation may negate the need to invest in physiological thermotolerance, further offering explanation for the lack of landscape effect on the physiological thermotolerance of larger carabids.

Keywords: agroecosystems; local adaptation; physiological thermal tolerance; plasticity; winter resistance.

Fig. 1

Observation arena developed to study carabid behavioral thermoregulation. The doubled‐walled nature of the arena, in conjunction with a secondary circuit built into the base, enabled the circulation of ethylene glycol from a programmable alcohol bath around the cylinder to control the temperature experienced within the arena. The floor of the arena was divided into 4 different substrates: (1) wheat grown in potting compost at a density of 15 blades of wheat and approximately 15 cm in height; (2) bare potting compost; (3) bare potting compost in which 3 holes of 1 cm in width and depth were drilled; and (4) potting compost with an artificial shelter. Dimensions are provided in mm.

Fig. 2

Carabid cold tolerance as measured by CT_min (±SE) sampled in the 3 landscape types: complex (comp), intermediate (inter), and simple (simp) considering all sampling seasons. Species are ordered by size, from smallest to largest. Each pairwise comparison between group level was calculated using a log‐rank test using the pairwise_survdiff function in R. Asterisks indicate significant P values: *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001.