Continuous Radar Tracking Illustrates the Development of Multi-destination Routes of Bumblebees

Joseph L Woodgate,Ka S Lim,Lars Chittka,James C Makinson,Andrew M Reynolds

doi:10.1038/s41598-017-17553-1

Joseph L Woodgate, Ka S Lim + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-17553-1

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Abstract

Animals that visit multiple foraging sites face a problem, analogous to the Travelling Salesman Problem, of finding an efficient route. We explored bumblebees’ route development on an array of five artificial flowers in which minimising travel distances between individual feeders conflicted with minimising overall distance. No previous study of bee spatial navigation has been able to follow animals’ movement during learning; we tracked bumblebee foragers continuously, using harmonic radar, and examined the process of route formation in detail for a small number of selected individuals. On our array, bees did not settle on visit sequences that gave the shortest overall path, but prioritised movements to nearby feeders. Nonetheless, flight distance and duration reduced with experience. This increased efficiency was attributable mainly to experienced bees reducing exploration beyond the feeder array and flights becoming straighter with experience, rather than improvements in the sequence of feeder visits. Flight paths of all legs of a flight stabilised at similar rates, whereas the first few feeder visits became fixed early while bees continued to experiment with the order of later visits. Stabilising early sections of a route and prioritising travel between nearby destinations may reduce the search space, allowing rapid adoption of efficient routes.

Highlights

The development of trapline routes in bees has been examined by recording the sequence of visits to flowers to infer the rules underlying route formation[3,9,10,11,12,13,15,16,17,18,19]
In the only study of trapline foraging at a large spatial scale to date, Lihoreau et al.[20] found that bees developed a repeatable trapline on a pentagonal feeder array, following the route which required the shortest possible flight path; this was the route that would result from use of a nearest-neighbour heuristic, where an agent always travels to the closest as-yet-unvisited location
Previous studies into multi-destination route formation have focussed on sequences of feeder visits but researchers have not been able to track the ontogeny of actual flight paths of their subjects[3,9,10,11,12,15,16,17,18,19,20]

Summary

Introduction

The development of trapline routes in bees has been examined by recording the sequence of visits to flowers to infer the rules underlying route formation[3,9,10,11,12,13,15,16,17,18,19]. Lihoreau et al developed a traplining heuristic model using a process of iterative improvement based on the overall length of each route tried[20,24], which reproduced a number of results seen in the behaviour of real bees[24], but predicted there are certain spatial configurations for which bees cannot form stable traplines that minimise travel distance, including the conflicting array used by Ohashi et al.[12]. In the only study of trapline foraging at a large spatial scale to date, Lihoreau et al.[20] found that bees developed a repeatable trapline on a pentagonal feeder array, following the route which required the shortest possible flight path; this was the route that would result from use of a nearest-neighbour heuristic, where an agent always travels to the closest as-yet-unvisited location (see Fig. 1). Because the distances and number of feeders were the same as those used by[20], any differences in performance must be attributable to the spatial configuration of the feeders

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