The affordable laboratory of climate change: devices to estimate ectotherm vital rates under projected global warming

Abstract

Determining organisms’ responses to novel temperatures is relevant from ecological, evolutionary, and conservation perspectives. Here, we have validated designs and included biological examples for three affordable devices to estimate thermal responses of ectotherms: (1) a water bath that can be programmed to increase temperatures to estimate an organismal critical thermal maximum (CTmax), (2) a miniature portable refrigerator to estimate an organism's critical thermal minimum (CTmin), and (3) inexpensive growth chambers that maintain constant temperatures or simulate dynamic environmental temperature patterns. We tested the reliability of the CTmax device at temperature increase rates of 1° and 2°C/min. Observed temperatures deviated 0.01°C and 0.02°C from target temperatures, respectively. The CTmin device easily attained target temperatures via manipulation of the input voltage. The maximum deviation from target temperatures in environmental chambers programmed to maintain constant temperatures between 10°C and 30°C was 0.8°C. Environmental chambers programmed to simulate temperature profiles of tropical rain and montane forests deviated from target temperatures by a maximum of −0.5°C to 0.9°C. Examples of applications show that (1) tropical insects at high elevations are less tolerant to high temperatures than insects in lowland forests, (2) nocturnal ants display lower CTmax and CTmin than diurnal ant species, and (3) experiments in growth chambers show high mortality of high-elevation insect species when exposed to temperatures that typify lowland forests, and high mortality of lowland insect species when exposed to temperatures that typify high elevations. The devices described in this study can be mass-produced inexpensively and are currently being used in laboratories in the United States, Mexico, and Costa Rica. The main goal of this project is to encourage the construction of affordable devices and the use of standardized methodologies to create a global network of researchers studying thermal responses in diverse taxa and geographic locations.