Behavioral/Systems/Cognitive Navigational Decision Making in Drosophila Thermotaxis

Amechanistic understanding of animal navigation requires quantitative assessment of the sensorimotor strategies used during naviga-tion and quantitative assessment of how these strategies are regulated by cellular sensors. Here, we examine thermotactic behavior of the Drosophila melanogaster larva using a trackingmicroscope to study individual larval movements on defined temperature gradients.We discover that larval thermotaxis involves a larger repertoireof strategies thannavigation in smaller organisms suchasmotile bacteria and Caenorhabditis elegans. Beyond regulating run length (i.e., biasing a randomwalk), theDrosophila melanogaster larva also regulates the size and direction of turns to achieve andmaintain favorable orientations. Thus, the sharp turns in a larva’s trajectory represent decision points for selecting new directions of forward movement. The larva uses the same strategies to move up temperature gradients during positive thermotaxis and to move down temperature gradients during negative thermotaxis. Disrupting positive thermotaxis by inacti-vating cold-sensitive neurons in the larva’s terminal organweakens all regulation of turning decisions, suggesting that information from one set of temperature sensors is used to regulate all aspects of turning decisions. The Drosophila melanogaster larva performs thermo-taxis by biasing stochastic turning decisions on the basis of temporal variations in thermosensory input, thereby augmenting the likelihood of heading toward favorable temperatures at all times