Visual sensitivity across the fiddler crab eye
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1
The University of Western Australia, School of Animal Biology & The UWA Oceans Institute, Australia
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2
The Australian National University, Research School of Biology, Australia
Despite a wealth of information about fiddler crab behaviour and how they deal with relatively limited eyesight, we still know very little about the sensitivity of the actual photoreceptor array and how visual information is processed. In this work in progress we use Electroretinogram (ERG) and Intracellular recordings from photoreceptors in order to characterise the visual input across the eyes of a number of fiddler crab species (Uca spp).
The compound eyes of fiddler crabs are highly regionalised with several adaptations in optical and sampling resolution across the visual field. They have a maximum acuity of about 1-2 cycles per degree, but across most of the visual field, resolution is much lower. Given this relatively poor eyesight, the crabs show surprisingly sophisticated behavioural discriminations and vision is one of the main sources of information they use when it comes to mate choice, species discrimination and predator avoidance. The crabs appear to use colour and pattern discrimination to distinguish between species and even conspecifics and are highly sensitive to approaching predators. Their sensitivity makes them very difficult to surprise. In the context of predator avoidance, the crabs show an interesting mix of simple rules of thumb and sophisticated decision making and learning abilities which are thought to be a result of their need to work around visual limitations.
During predator avoidance in their natural environment, the crabs respond very early - when the retinal image of a predator is still very small and moves very slowly. At this point, crabs respond to retinal motion and flicker. These criteria do not accurately reflect the risk posed by the moving objects, but are safe and very likely closely linked to photoreceptor sensitivities.
Initial ERG recordings confirm that the spectral sensitivity of the crabs eyes extends from the UV into the yellow/red, with a strong peak in the blue-green part of the spectrum. This agrees well with intracellular recordings in which most photoreceptors peak around 450-470nm. As indicated from behavioural observations, a large number of photoreceptors are polarisation sensitive.
Flicker-ERG recordings from the fiddler crab Uca elegans, suggest a flicker-fusion-frequency of just over 100 Hz. The amplitude-frequency plot has a slightly unusual shape with three peaks. After an initial, fast drop in response amplitude below 10Hz, the curve is broad and shows a slow decline.
Acknowledgements
This research was supported by ARC Centre of Excellence in Vision Science (CE0561903) and a Future Fellowship to JMH
Keywords:
Flicker Fusion,
Polarisation,
fiddler crabs,
Spectral sensitivity,
Vision
Conference:
International Conference on Invertebrate Vision, Fjälkinge, Sweden, 1 Aug - 8 Aug, 2013.
Presentation Type:
Oral presentation preferred
Topic:
Colour and polarisation vision
Citation:
Hemmi
JM and
Falkowski
M
(2019). Visual sensitivity across the fiddler crab eye.
Front. Physiol.
Conference Abstract:
International Conference on Invertebrate Vision.
doi: 10.3389/conf.fphys.2013.25.00066
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Received:
31 May 2013;
Published Online:
09 Dec 2019.
*
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