The role of body mass in limiting post heat-coma recovery ability in terrestrial ectotherms

Abstract

Under global warming, animal species show shrinking body size responses, cascading deep changes in community structure and ecosystem functions. Although the exact physiological mechanisms behind this phenomenon remain unsolved, smaller individuals may benefit from warming climate more than larger ones. Heat-coma, a physiological state with severe consequences on locomotion ability, is often considered as an "ecological death" scenario under which individuals are unable to escape and exposed to predation, further heat injury, and other hazards. Species are expected to increasingly encounter heat-coma temperature thresholds under warming climate, and body size may be an important trait for thermoregulation in particular for ectotherms. The relationship between heat-coma and shrinking body size remains, however, unclear. Yet, recovery after short-term heat-coma is possible, but little is known about its importance in thermal adaptation and how organismal size correlates with post heat-coma recovery. Here, using ants as a model system, we firstly examined the fate of heat-comatose individuals under field conditions to quantify the ecological benefits of post heat-coma recovery. Then, we quantified ants' recovery ability after heat-coma using a dynamic thermal assay in the laboratory and asked if thermal resilience varies between species with different body mass. Our results confirm that heat-coma represents an inherent ecological death where individuals failed to recover from coma suffer strong predation pressure. Additionally, following phylogenetic signals inclusion, organisms with small mass were more likely to recover, supporting the temperature-size rule in thermal adaptation and recent studies showing a decrease in body size composition of ectotherm community under warmer climatic conditions. Body size as a fundamental trait in ecology thus affects ectotherm survival under thermal stress, which may drive species body size adaptations and community composition under future warming scenarios.

Keywords: ecophysiology; fitness; heat shock; recovery; thermal resilience.