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Great attachment on slippery ground
Scientists of Kiel University analyse attachment in flowing waters
It’s a well-known problem: When biofilm grows on river stones and pebbles, they become extremely slippery. Scientists of Kiel University have discovered that for small animals, this effect is reversed. The so-called biofilm, a slimy film consisting of algae, bacteria and other organic matter, provides insects and their larvae with additional hold. Especially in flowing waters such as streams and riverson this is decisive for the colonization of smooth substrates exposed to strong currents. These findings were published in the renowned scientific magazine „Journal of the Royal Society Interface“, on December 18, 2013.
A series of tests with the larvae of the freshwater mayfly Epeorus assimilis have proven that the biofilm is not only important for the insects as a source of food, but also in questions of attachment. The team of scientists, consisting of bio-physicist Alexander Kovalev and biologists Stanislav Gorb, Jan Michels, Jochen Koop and Petra Ditsche, have found that, in contrast to humans or vehicles, insects are able to apply their attachment mechanisms on slippery biofilm. Even though the larvae’s claws are not able to cling to primary smooth surfaces, they can penetrate the slimy biofilm and interlock their claws with organisms inside of the biofilm. Moreover, the high viscosity of the biofilm strengthens the insects’ ability to resist the current. “It’s like sticking your feet in honey”, explains Dr. Petra Ditsche, member of the work group Functional Morphology and Bio-Mechanics at Kiel University.
In the laboratory, artificial substrates with various levels of roughness were produced – ranging from extremely smooth to extremely rough. The scientists let biofilm grow over a subset of these substrates. Following this process, the overgrown substrates were compared with the bare substrates of the same type. The surface structure was measured by confocal laser scanning microscopy (CLSM) and analysed to quantify roughness. Indentation measurements were used to determine the biophysical characteristics of biofilm, such as elasticity and hardness. The larvae’s ability to hold onto the substrate was tested in an artificial flume. This test determined the maximum speed at which the larvae were able to cling to a certain kind of substrate. Further, the claws’ retention force (such as friction and clamping) was tested. For this purpose, the scientists fixed specimens of dissected claws on a specific force sensor. The claws were oriented in a natural position and pulled parallel to the particular substrate by a micromanipulator, while forces were recorded.
These tests have shown that it is important to consider the biofilm when analysing attachment in aquatic environments because it changes the characteristics of substrates considerably. In the case of the mayfly larvae examined, the attachment forces were stronger on substrates covered with biofilm. That was particularly the case with substrates that were smooth, as well as the ones that displayed only slight roughness. All of them did not provide sufficient surface irregularities for interlocking of the claw. For this reason biofilm should be taken into consideration as a relevant factor influencing attachment on a surface. This applies not only to sessile organisms but also for mobile animals.
Moreover, these findings can inform future work in other fields, such as antifouling research or the development of artificial attachment devices for underwater purposes.
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SEM image of the tarsal claw of E assmilis fore leg. Photo/Copyright: Petra Ditsche
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Underwater image of E assimilis. Photo/Copyright: Petra Ditsche
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Work Group „Functional Morphology and Biomechanics“, at the Institute of Zoology:
Journal of the Royal Society Interface:
Dr. Petra Ditsche
Friday Harbor Laboratories
University of Washington
620 University Road
Friday Harbor, WA, 98250
Email: pditsche@UW.edu, firstname.lastname@example.org
Prof. Dr. Stanislav Gorb
Functional Morphology and Biomechanics
Institute of Zoology
Christian-Albrechts-Universität zu Kiel
Am Botanischen Garten 1-9
phone.: +49 (0) 431/880 4859
Ditsche P, Michels J, Kovalev A, Koop J, Gorb S. 2014 More than just slippery: the impact of biofilm on the attachment of non-sessile freshwater mayfly larvae. J. R. Soc. Interface 20130989.
Press, Communication and Marketing, Dr. Boris Pawlowski
Address: D-24098 Kiel, phone: +49 (0431) 880-2104, fax: +49 (0431) 880-1355
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Text / Redaktion: Sebastian Maas