Predator avoidance: The highly flexible and context dependent escape decisions in Fiddler crabs
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1
The University of Western Australia, School of Animal Biology, The UWA Oceans Institute, Australia
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2
University of Melbourne, Zoology Department, Australia
Crabs have proven to be a valuable model system for the study of the neural control of the ‘escape response’(1). Their main advantages are that they allow study of their escape responses both under natural field conditions, as well as under controlled laboratory conditions, and that we are able to trace the neural pathways that lead to escape responses in behaving animals. We present here results from laboratory experiments in fiddler crabs that exploit this versatility in order to test to what extent escape responses are shaped by the physical and behavioural context in which the animal finds itself.
The compound eyes of fiddler crabs offer little accurate information about the level of threat posed by objects moving in the crabs’ environment. As a consequence, fiddler crabs have been shown to use a range of different strategies to decide when to run towards the safety of their burrow when attacked. In their natural environment, the crabs respond very early - when the retinal image of a predator still appears very small and moves very slowly. At this point, crabs respond to retinal motion and flicker – response criteria that are safe, but do not accurately reflect the risk posed by the moving objects. This contrasts sharply with reports from laboratory experiments, where other crab species respond much later – at larger apparent sizes – and where crabs time their escape decision according to more informative decision criteria, such as the increases in angular size of the stimulus during its approach. The lobula giant neurons that are thought responsible for the escape decision have been described in detail(2).
Here we present results from laboratory experiments in fiddler crabs (Uca vomeris) to show that, under laboratory conditions, these crabs change their escape criteria from those used when they are tested in their natural environment. The crabs respond significantly later in the lab than in field experiments, use different response criteria and run directly away from the approaching object. The results further confirm that the decision when to escape from a predator is highly context dependent and different criteria are used in different situations. It is likely that the same lobula giant neurons underlie both laboratory and natural responses. How such context dependency is implemented on the neural level, however, remains to be determined.
(1) Hemmi JM & Tomsic D (2011). The neuroethology of escape in crabs: from sensory ecology to neurons and back. Curr Opin Neurobiol doi: 10.1016/j.conb.2011.11.012
(2) Medan V, Oliva D & Tomsic D (2007). Characterization of lobula giant neurons responsive to visual stimuli that elicit escape behaviors in the crab chasmagnathus. J Neurophysiol, 98, 2414-2428.
Acknowledgements
ARC Centre of Excellence Program
ARC Future Fellowship (FT110100528)
Keywords:
context,
Decision Making,
Escape,
fiddler crabs,
predation,
Vision
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Sensory: Vision
Citation:
Hemmi
JM and
VanAsten
T
(2012). Predator avoidance: The highly flexible and context dependent escape decisions in Fiddler crabs.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00371
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Received:
01 May 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Jan M Hemmi, The University of Western Australia, School of Animal Biology, The UWA Oceans Institute, Perth, WA, 6009, Australia, jan.hemmi@uwa.edu.au