How hot is too hot? Metabolic responses to temperature across life stages of a small ectotherm.

To understand how global warming will impact biodiversity, we need to pay attention to those species with higher vulnerability. However, to assess vulnerability we also need to consider the thermoregulatory mechanisms, body size and thermal tolerance of species. Studies addressing thermal tolerance on small ectotherms have mostly focused on insects, while other arthropods such as arachnids remain understudied. Here, we quantified the physiological thermal sensitivity of the pseudoscorpion Dactylochelifer silvestris using a respirometry setup with a ramping temperature increase. Overall, we found that D. silvestris has a much lower metabolic rate than other organisms of similar size. As expected, metabolic rate increased with body size, with adults having larger metabolic rates, but the overall metabolic scaling exponent was low. Both the temperature at which metabolism peaked and the critical thermal maxima were high (above 44°C) and comparable to those of other arachnids. The activation energy, which characterizes the rising portion of the thermal sensitivity curve, was 0.66 eV, consistent with predictions for insects and other taxa in general. Heat tolerances and activation energy did not differ across life stages. We conclude that D. silvestris has low metabolic rates and a high thermal tolerance, which would likely influence how all stages and sexes of this species could endure climate change.