Data from: History dependence in insect flight decisions during odor tracking

Natural decision-making often involves extended decision sequences in
response to variable stimuli with complex structure. As an example, many
animals follow odor plumes to locate food sources or mates, but turbulence
breaks up the advected odor signal into intermittent filaments and puffs.
This scenario provides an opportunity to ask how animals use sparse,
instantaneous, and stochastic signal encounters to generate goal-oriented
behavioral sequences. Here we examined the trajectories of flying fruit
flies (Drosophila melanogaster) and mosquitoes (Aedes aegypti) navigating
in controlled plumes of attractive odorants. While it is known that mean
odor-triggered flight responses are dominated by upwind turns, individual
responses are highly variable. We asked whether deviations from mean
responses depended on specific features of odor encounters, and found that
odor-triggered turns were slightly but significantly modulated by two
features of odor encounters. First, encounters with higher concentrations
triggered stronger upwind turns. Second, encounters occurring later in a
sequence triggered weaker upwind turns. To contextualize the latter
history dependence theoretically, we examined trajectories simulated from
three normative tracking strategies. We found that neither a purely
reactive strategy nor a strategy in which the tracker learned the plume
centerline over time captured the observed history dependence. In
contrast, “infotaxis”, in which flight decisions maximized expected
information gain about source location, exhibited a history dependence
aligned in sign with the data, though much larger in magnitude. These
findings suggest that while true plume tracking is dominated by a reactive
odor response it might also involve a history-dependent modulation of
responses consistent with the accumulation of information about a source
over multi-encounter timescales. This suggests that short-term memory
processes modulating decision sequences may play a role in natural plume
tracking.