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Color changing sand fleas flummox predatory birds

Sand fleas have a remarkable ability to change colour in order to match dramatically different backgrounds, according to a new study

University of Exeter

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IMAGE: The researchers studied a species of sand flea (or mole crab) (Hippa testudinaria), which lives on the beaches of Ascension island. They showed that the brightness and the coloration of... view more

Credit: Alice Lown / Martin Stevens

Sand fleas have a remarkable ability to change colour in order to match dramatically different backgrounds, according to a new study from the University of Exeter and the Ascension Island Government Conservation Department.

The research found that sand fleas from the remote British Overseas Territory of Ascension Island change their colour to match the beaches they wash up on, which vary widely in colour and brightness from black to light yellow.

Sand fleas occupy the swash zone of sandy beaches where they are exposed to a range of visually-guided predators, including shorebirds and crabs. To simulate this situation the study, published in the Royal Society journal Biology Letters, used cutting edge camera technology to view the camouflaged sand fleas through the eyes of predatory birds.

Dr Martin Stevens from the Centre for Ecology and Conservation at the University of Exeter's Penryn Campus said: "As far as we know, this is the first time that research has demonstrated through the eyes of a predator how individual animals from the same population can tune their camouflage to match different backgrounds. Most previous studies have relied on human assessments of appearance, but predators often see the world very differently to humans. Our work shows how animals living in a small geographic area can modify their appearance over time to match their respective environment."

Dr Sam Weber from Ascension Island Government said: "We first noticed the close colour matching of sand fleas to their environment during research into the turtles that nest on Ascension's shores. However, it was only after teaming up with colleagues at the University of Exeter that the full extent and sophistication of the camouflage became apparent."

Unlike many populations of animals that undergo genetic changes over numerous generations and improve their camouflage against the environment, sand fleas from the different beaches begin life as a planktonic larval stage and so are likely to come from the same gene pool. They then wash up on any beach, and so genetic adaptation to any specific beach colour is very unlikely. Instead they must change colour to match their own beach and they apparently do this as they moult, growing closer to the beach colour as they develop into adults.

The sand fleas, also known as mole crabs, were photographed in the lab along with sand from their respective beaches. The images were transformed to correspond to an avian visual system using software specially designed by the team to determine how camouflaged the fleas would appear to a predatory bird. The results showed that the sand fleas matched the colour and brightness of the beaches they lived on, affording them camouflage against predators.

Future work will focus on the underlying mechanisms involved in developmental changes in colouration, including the role of visual feedback and cellular processes.

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The research received funding from the Biotechnology and Biological Sciences Research Council (BBSRC), the Darwin Initiative and Ascension Island Government.

Phenotype-Environment Matching in Sand Fleas by Martin Stevens, Annette C. Broderick, Brendan J. Godley, Alice E. Lown, Jolyon Troscianko, Nicola Weber, and Sam B. Weber is published in Biology Letters.

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About the University of Exeter

The University of Exeter is a Russell Group university and in the top one percent of institutions globally. It combines world-class research with very high levels of student satisfaction. Exeter has over 19,000 students and is ranked 7th in The Times and The Sunday Times Good University Guide league table, 10th in The Complete University Guide and 9th in the Guardian University Guide 2015. In the 2014 Research Excellence Framework (REF), the University ranked 16th nationally, with 98% of its research rated as being of international quality. Exeter was The Sunday Times University of the Year 2012-13.

The University has four campuses. The Streatham and St Luke's campuses are in Exeter and there are two campuses in Cornwall, Penryn and Truro. The 2014-2015 academic year marks the 10-year anniversary of the two Cornwall campuses. In a pioneering arrangement in the UK, the Penryn Campus is jointly owned and managed with Falmouth University. At the campus, University of Exeter students can study programmes in the following areas: Animal Behaviour, Conservation Biology and Ecology, English, Environmental Science, Evolutionary Biology, Geography, Geology, History, Human Sciences, Marine Biology, Mining and Minerals Engineering, Politics and International Relations, Renewable Energy and Zoology.

The University has invested strategically to deliver more than £350 million worth of new facilities across its campuses in the past few years; including landmark new student services centres - the Forum in Exeter and The Exchange at Penryn - together with world-class new facilities for Biosciences, the Business School and the Environment and Sustainability Institute. There are plans for another £330 million of investment between now and 2016.

http://www.exeter.ac.uk/cornwall

About the University of Exeter's Centre for Ecology and Conservation (CEC)

Staff at the Centre for Ecology and Conservation, based on the Penryn Campus, undertake cutting-edge research that focusses on whole organism biology. The CEC has three interlinked research groups: Behaviour, Ecology and Conservation, and Evolution which constitute 40 academics and over 100 early career researchers. It engages widely with businesses, charities and government agencies and organisations in Cornwall, the Isles of Scilly and beyond to translate its research into societal impact. Staff at the CEC deliver educational programs to some 500 undergraduate and 100 postgraduate students.

A new £5.5 million Science and Engineering Research Support Facility (SERSF) is currently under construction at the Penryn Campus. The facility will bring pioneering business, science and engineering together and will provide space for the growing CEC alongside the University of Exeter Business School, which is expanding into Cornwall, and the University's Marine Renewables team.

The University of Exeter and Falmouth University are founding partners in the Combined Universities in Cornwall (CUC), a unique collaboration between six universities and colleges to promote regional economic regeneration through Higher Education, funded mainly by the European Union (Objective One and Convergence), the South West Regional Development Agency and the Higher Education Funding Council for England, with support from Cornwall Council.

http://biosciences.exeter.ac.uk/cec/

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