Cold trapped - Correcting locomotion dependent observation biases in thermal preference of Drosophila

Sensing environmental temperatures is essential for the survival of ectothermic organisms. In Drosophila , two methodologies are used to study temperature preferences (T P ) and the genes involved in thermosensation: two-choice assays and temperature gradients. Whereas two-choice assays reveal a relative T P , temperature gradients can identify the absolute T P . One drawback of gradients is that small ectothermic animals are susceptible to cold-trapping: a physiological inability to move at the cold area of the gradient. Often cold-trapping cannot be avoided, biasing the resulting T P to lower temperatures. Two mathematical models were previously developed to correct for cold-trapping. These models, however, focus on group behaviour which can lead to overestimation of cold-trapping due to group aggregation. Here we present a mathematical model that estimates the behaviour of individual Drosophila in temperature gradients. The model takes the spatial dimension and temperature difference of the gradient into account, as well as the rearing temperature of the flies. Furthermore, it allows quantifying cold-trapping, reveals true T P , and differentiates between temperature preference and tolerance. Online simulation is hosted at http://igloo.uni-goettingen.de. The code can be accessed at https://github.com/zerotonin/igloo .