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How Bumblebees Tackle the Travelling Salesman Problem
29 June 2011
It is a mathematical puzzle which has vexed academics and travelling salesmen alike, but new research published in the British Ecological Society’s Functional Ecology, reveals how bumblebees effectively plan their route between the most rewarding flowers while travelling the shortest distances.
The research, led by Dr Mathieu Lihoreau from Queen Mary, University of London, explored the movement of bumblebees, Bombus terrestris, as they collected nectar from five artificial flowers varying in reward value.
“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,” said Dr Lihoreau, “While trap-lining is a common foraging strategy found in bees, birds and primates we still know very little about how animals attempt to optimise the routes they travel.”
Research into optimising routes based on distance and the size of potential rewards is reminiscent of the well known Travelling Salesman problem in mathematics, which was first formulated in 1930, but remains one of the most intensively studied problems in optimisation.
“The Travelling Salesman must find the shortest route that allows him to visit all locations on his route,” explained co-author Dr Nigel Raine, “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 set up a bee nest-box, marking each bumblebee with numbered tags 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,” said Dr Lihoreau. “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.”
In a feat of spatial judgement the bees decided that if visiting the high reward flower added only a small increase in travel distance, they switched to visiting it first. 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.
“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.”
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Notes for Editors
This study is published in the British Ecological Society's Functional Ecology. Media wishing to receive a PDF of this article may contact Lifesciencenews@wiley.com
Full citation: Lihoreau M, Chittka L, Raine NE, "Trade-off between travel distance and prioritization of high reward sites in trap-lining bumblebees", Functional Ecology, Wiley-Blackwell, July 2011, DOI: 10.1111/j.1365-2435.2011.01881.x
URL Upon publication: http://doi.wiley.com/10.1111/j.1365-2435.2011.01881.x
The work has been funded by the Wellcome Trust, Biotechnology and Biological Sciences Research Council, Engineering and Physical Sciences Research Council.
About the Author:
Mathieu Lihoreau is a postdoctoral researcher now working at the University of Sydney (formerly at Queen Mary, University of London). He has worked on the social ecology of a wide range of insects including cockroaches, bumblebees and locusts.
Lars Chittka is Professor of Sensory and Behavioural Ecology at Queen Mary, University of London. He has more than 20 years research experience with bees, working on their sensory systems, navigation, cognition and communication.
Nigel Raine is Senior Lecturer in Animal Behaviour at Royal Holloway University of London (formerly at Queen Mary, University of London). He has worked extensively on bee behaviour and pollination, particularly on how learning helps bees adapt to their environment and find the best flowers.
Author Interview:
Siān Halkyard, Communications Manager (Science and Engineering), Queen Mary, University of London, 020 7882 7454
About the Journal:
Functional Ecology publishes original papers in organismal ecology, including physiological ecology, behavioural ecology and evolutionary ecology, and their implications for community and ecosystem patterns and processes. Papers may describe experimental, comparative or theoretical studies on any types of organism. Work that is purely descriptive, or that focuses on population dynamics (without investigation of the underlying factors influencing population dynamics) will not be accepted unless it sheds light on those specific areas mentioned above.
http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2435
Functional Ecology is published by Wiley-Blackwell for the British Ecological Society. Contents lists are available at www.functionalecology.org
The British Ecological Society is a learned society, a registered charity and a company limited by guarantee. Established in 1913 by academics to promote and foster the study of ecology in its widest sense, the Society has 4,000 members in the UK and abroad. Further information is available at www.britishecologicalsociety.org
About Queen Mary, University of London:
Queen Mary, University of London is one of the UK's leading research-focused higher education institutions with some 16,000 undergraduate and postgraduate students.
Amongst the largest of the colleges of the University of London, Queen Mary's 3,000 staff deliver world-class degree programmes and research across three faculties: Science and Engineering; Humanities and Social Sciences and the School of Medicine and Dentistry.
Queen Mary, as a member of the 1994 Group of research-focused universities, has made a strategic commitment to the highest quality of research, but also to the best possible educational, cultural and social experience for its students. The College is unique among London's universities in being able to offer a completely integrated residential campus, with a 2,000-bed award-winning Student Village on its Mile End campus.
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