Thermotactic Decision-Making in Aquatic Invertebrates: High-Resolution Behavioral Analysis of Ecotoxicological...

Thermotaxis, the directed movement of organisms in response to temperature gradients, represents a fundamental behavioral strategy in ectothermic species. Here we present a fully programmable thermoelectric platform designed for high-throughput analysis of thermotactic behaviors in a small aquatic model species. The platform integrates microcontroller-controlled Peltier elements with closed-loop feedback and automated infrared-based tracking to generate stable thermal gradients or binary zones for high-throughput behavioral analysis. Validation experiments using groups of 25 individuals of Daphnia carinata demonstrated clear thermal preferences, with animals preferentially occupying the 22 °C zone for ∼70% of the trial duration under binary conditions and ∼40% under gradient conditions. Behavioral responses rapidly followed dynamic zone-swapping and were aligned with thermal changes, indicating nonrandom movement. Environmental variables, including population density, feeding status, and genetic background, also influenced thermal preference behaviors. Pharmacological inhibition of TRPA1 and TRPM3 produced temperature-specific behavioral shifts. Finally, proof-of-concept ecotoxicological assays showed that short-term (12 h) acute exposure to neuroactive pollutants, including diazepam and chlorpyrifos, significantly perturbed thermal preference behaviors and locomotor activity. These results establish thermotaxis as a sensitive behavioral end point for ecotoxicology and provide a versatile platform for temperature-driven studies in aquatic taxa.