Abstract
Sensitivity to temporal information and the ability to adjust behavior
to the temporal structure of the environment should be phylogenetically
widespread. Some timing abilities, such as sensitivity to circadian
cycles, appear in a wide range of invertebrate and vertebrate taxa
1,2. Interval timing--sensitivity to the duration of time intervals--has,
however, only been shown to occur in vertebrates 3,4. Insect pollinators
make a variety of decisions that would appear to require the ability
to estimate elapsed durations. We exposed bumble bees to conditions
in which proboscis extension was reinforced after a fixed duration
had elapsed or after either of two fixed durations had elapsed. Two
groups of bees were trained with a short duration (either 6 s or
12 s) and a long duration (36 s) in separate experimental phases
(independent timing groups), whereas two other groups were trained
with a short duration (either 6 s or 12 s) and long duration (36
s) always intermixed unpredictably (multiple timing groups). On long
intervals, independent timing groups waited longer than mixed timing
groups to generate the first response and responded maximally near
the end of the interval. Multiple timing groups waited the same amount
of time on average before generating the first response on both long
and short intervals. On individual trials, multiple timing groups
appeared to time either the long duration only or both the short
and long durations: most trials were characterized by a single burst
of responding that began between the short and long duration values
or by two bursts of responding with the first burst bracketing the
short value and the second burst beginning in anticipation of the
long value. These results show that bumble bees learn to time interval
durations and can flexibly time multiple durations simultaneously.
The results indicate no phylogenetic divide between vertebrates and
invertebrates in interval timing ability.
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