British researchers believe they have unlocked the mystery of how bumblebees plan their route between the most nectar-laden flowers while travelling the shortest distances, a puzzle that has long vexed academics.
New research from University of London’s School of Biological and Chemical Sciences explored the movement of bumblebees as they collected nectar from five artificial flowers varying in reward value.
The research into optimizing routes based on distance and the size of potential rewards, led by Dr. Mathieu Lihoreau and published in the British Ecological Society’s Functional Ecology, is reminiscent of Traveling Salesman problem in mathematics, first formulated in 1930 but still one of the most intensively studied problems in optimization, according to Pysorg.com.
“Animals which forage on resources that are fixed in space and replenish over time, such as flowers which refill with nectar, often visit these resources in repeatable sequences called trap-lines,” Lihoreau said. “While trap-lining is a common foraging strategy found in bees, birds and primates we still know very little about how animals attempt to optimize the routes they travel.”
In the well-known Traveling Salesman problem the salesman must find the shortest route that allows him to visit all locations on his route, co-author Dr. Nigel Raine said. “Computers solve it by comparing the length of all possible routes and choosing the shortest. However, bees solve simple versions of it without computer assistance using a brain the size of grass seed.”
The team was able to gain insight into how the bumblebees’ strategy for securing nectar by setting up a bee nest-box and tagging each bumblebee with number to allow them to follow their behaviour when allowed to visit five artificial flowers which were arranged in a regular pentagon.
“When the flowers all contain the same amount of nectar bees learned to fly the shortest route to visit them all,” Lihoreau said. “However, by making one flower much more rewarding than the rest we forced the bees to decide between following the shortest route or visiting the most rewarding flower first.”
Interestingly, the bees decided that if visiting the high-reward flower added only a small increase in travel distance, they switched to visiting it first, according to Pysorg.com. However, when visiting the high reward added a substantial increase in travel distance they did not visit it first.
The results revealed a trade-off between either prioritising visits to high reward flowers or flying the shortest possible route. Individual bees attempted to optimise both travel distance and nectar intake as they gained experience of the flowers, Pysorg.com added.
“We have demonstrated that bumblebees make a clear trade-off between minimising travel distance and prioritising high rewards when considering routes with multiple locations,” concluded co-author Professor Lars Chittka.
“These results provide the first evidence that animals use a combined memory of both the location and profitability of locations when making complex routing decisions, giving us a new insight into the spatial strategies of trap-lining animals,” he added.