The native crayfish suffers from two parasites; plague, which is carried by the American invader, as well as porcelain disease which makes the native crayfish sluggish and suppresses their appetite before eventually killing them a few years later.
Yorkshire is one of the last strongholds of the white-clawed crayfish, which is being driven out of Britain's waterways by its hardier American cousin, introduced to Britain in the 1970s for fish farming. The advance of the signal crayfish over its native rival has implications for the biodiversity of Britain's rivers as the diversity of prey is reduced and the invaders' appetite for fish eggs causes a decline in the fish population.
Although the white-clawed crayfish is listed as an endangered species in Britain, the reasons for its decline and the American species' success have not been well understood. Now, researchers from the University of Leeds' Faculty of Biological Sciences have been trying to work out why the signal crayfish has been gaining the upper hand, and how this information might be used in conservation projects.
Their study, published in the online journal PLoS One, compares how quickly the two different species deal with food. The American signal crayfish ate up to 83 per cent more food per day than did their native cousins. The research also showed that white-clawed crayfish are much more choosy about what they eat, preferring particular types of prey, while the signals eat equal amounts of all prey. The white-clawed crayfish are also affected by a common parasite, porcelain disease, which affects their ability to catch prey, leading affected crayfish to eat 30% less. The American signal crayfish, on the other hand, seem unaffected by the parasite.
Dr Alison Dunn, of the Faculty of Biological Sciences, at the University of Leeds, who led the study, explains: "The signals eat much more compared with the native crayfish. But the situation is exacerbated by a parasite which essentially changes the native's behaviour - the white-clawed crayfish can't eat or handle as much food as the signal, because the parasite weakens its muscles."
"The huge appetites of the signal crayfish can have a massive effect on the whole ecosystem," adds Dr Dunn. "In particular it affects biodiversity because there is a reduction in the numbers of prey. In some Yorkshire rivers, for example, the fish population has declined because signal crayfish are eating large numbers of fish eggs."
Dr Dunn believes studying the effects of parasites on host species can offer vital clues about species conservation.
"Parasites are a fascinating and vital part of any ecosystem and you have to consider their effects when looking at biological invasions," she says. "We hope our findings will help us make predictions about how this invader might spread and help with management strategies."
Humans too can play a part in protecting the white-clawed crayfish by understanding how invading species spread. The signal crayfish is able to move overland of its own accord, but may also be inadvertently moved around in, for example, damp fishing gear.
"We need to be much more careful about how we move animals and plants around from habitat to habitat, and raise public awareness about these issues," says Dr Dunn.
The research was funded by the Natural Environment Research Council, in partnership with the Environment Agency. It is one of many projects run by the Yorkshire Dales Environment Network www.yden.leeds.ac.uk , set up to care for and manage the Yorkshire Dales.
Jessica Kwok and Ronaldo Ichiyama, International Spinal Research Trust (Feb 2018), £94,450
Dave Lewis and Colleagues in South Africa, HEFCE Global Challenge Research (Jan 2018), £48,000
Sarah Calaghan, Ed White, John Colyer, Isuru Jayasinghe, BHF (Jan 2018), £128,308
Christine Foyer and Alison Baker, HEFCE GCRF Grant (Jan 2018), £71,158
Alison Baker, Yun Yung Gong and Lindsay Stringer and ICRISAT India, HEFCE GCRF Grant (Jan 2018), £27,000
Graham Askew, Simon Walker, BBSRC (Jan 2018), £699,781
Jennifer Tomlinson, Royal Society (Jan 2018), £512,801
Alison Dunn, NERC (Dec 2017), £18,000
Jennifer Tomlinson, Royal Society-Research Fellows Enhancement Award (Dec 2017), £94,681
Helen Miller, AB AGri Grant (Dec 2017), £73,600
Simon Walker, Royal Society Enhancement Award (Dec 2017), £10,000
Carrie Ferguson, Bryan Taylor, Harry Rossiter, The Physiological Society (Dec 2017), £7,392
Ralf Richter, Royal Society (Dec 2017), £6,000
Christine Foyer, British Council Newton Fund (Dec 2017), £49,840
Adrian Whitehouse and colleagues in School of Chemistry and University of Liverpool, MRC (Nov 2017), £622,319
Michelle Peckham, Neil Ransom, MRC (Nov 2017), £495,159
Dave Lewis, British Council India (Nov 2017), £22,540
Hannah Dugdale, Royal Society (Nov 2017), £15,000
Elton Zeqiraj, Royal Society (Nov 2017), £15,000
Shaunna Burke, Cancer Research UK Innovation Grant (Nov 2017), £20,000
Alex O'Neill and colleagues in Chemistry, BBSRC (Nov 2017), £431,865
Jessica Kwok, Wings for Life (Nov 2017), £87,365
Tom Bennett, BBSRC (Oct 2017), £523,679
Neil Ranson, Darren Tomlinson, BBSRC (Oct 2017), £494,318
Nikita Gamper, BBSRC (Oct 2017), £490,426
Amanda Bretman and colleagues from UEA, NERC (Oct 2017), £430,886
Juan Fontana, Rosetrees Trust consumables grant (Oct 2017), £22,500
Helen Miller, DSM Nutritional Products AG (Sep 2017), £69,988
Neil Ranson, Juan Fontana, Mark Harris, Michelle Peckham, Ralf Richter, Peter Stockley, Patricija Van Oosten-Hawle and colleagues in Engineering, FMH and MAPS, Wellcome Trust Equipment Call (Sep 2017), £418,000
Jamie Johnston, Physiological Society (Sep 2017), £10,000
Frank Sobott, Adrian Goldman, Mark Harris, Andrew Macdonald, Stephen Muench, Sheena Radford and colleagues in FMH and MAPS, Wellcome Trust Equipment Call (Aug 2017), £415,000
Ralf Richter, David Brockwell, Eric Hewitt, Jessica Kwok, Emanuele Paci and MAPS/FMH, BBSRC (Jun 2017), £600,000
Eric Blair, Adrian Whitehouse, Nicola Stonehouse, Alison Baker, Richard Bayliss, Joan Boyes, Ryan Seipke, Sally Boxall and MAPS/FMH, BBSRC (Jun 2017), £376,000
Stefan Kepinski, Yoselin Benitez-Alfonso, Tom Bennett, Michelle Peckham, BBSRC (Jun 2017), £331,000
Roman Tuma, Lars Jeuken, Paul Millner, Sheena Radford, Peter Stockley and MAPS/FMH, BBSRC (Jun 2017), £222,000
Vas Ponnambalam, Darren Tomlinson, Stephen Wheatcroft, BHF (May 2017), £107,878
Graham Askew in collaboration with Bangor University, BBSRC (Mar 2017), £477,383
Stephen Muench, BBSRC (Mar 2017), £132,945
Nic Stonehouse, MRC (Mar 2017), £906,341
Bill Kunin, Steve Sait, BBSRC (Mar 2017), £602,831
Adrian Goldman, EU (Mar 2017), £546,576
Sheena Radford, Wellcome Trust (Mar 2017), £1,836,482
Tom Bennett, Royal Society (Mar 2017), £15,000
Jamie Johnston, Royal Society (Mar 2017), £15,000
Beatrice Filippi, Royal Society (Mar 2017), £15,000