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First published online February 15, 2008
Journal of Experimental Biology 211, 816-823 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.010546

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Vision in the nocturnal wandering spider Leucorchestris arenicola (Araneae: Sparassidae)

Thomas Nørgaard^1,*, Dan-Eric Nilsson², Joh R. Henschel³, Anders Garm² and Rüdiger Wehner¹

¹ Department of Zoology, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
² Department of Cell and Organism Biology, University of Lund, Helgonavägen 3, Lund, Sweden
³ Gobabeb Training and Research Centre, PO Box 953, Walvis Bay, Namibia

^* Author for correspondence at present address: Forschungsinstitut Senckenberg, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany (e-mail: noergaard.thomas{at}gmail.com)

Accepted 2 January 2008

At night the Namib Desert spider Leucorchestris arenicola performs long-distance homing across its sand dune habitat. By disabling all or pairs of the spiders' eight eyes we found that homing ability was severely reduced when vision was fully abolished. Vision, therefore, seems to play a key role in the nocturnal navigational performances of L. arenicola. After excluding two or three pairs of eyes, the spiders were found to be able to navigate successfully using only their lateral eyes or only their anterior median eyes. Measurement of the eyes' visual fields showed that the secondary eyes combined have a near full (panoramic) view of the surroundings. The visual fields of the principal eyes overlap almost completely with those of the anterior lateral eyes. Electroretinogram recordings indicate that each eye type contains a single photopigment with sensitivity peaking at 525 nm in the posterior and anteriomedian eyes, and at 540 nm in the anteriolateral eyes. Theoretical calculations of photon catches showed that the eyes are likely to employ a combination of spatial and temporal pooling in order to function at night. Under starlit conditions, the raw spatial and temporal resolution of the eyes is insufficient for detecting any visual information on structures in the landscape, and bright stars would be the only objects visible to the spiders. However, by summation in space and time, the spiders can rescue enough vision to detect coarse landscape structures. We show that L. arenicola spiders are likely to be using temporal summation to navigate at night.

Key words: nocturnal navigation, visual field, electroretinogram, spectral sensitivity, temporal summation, spider navigation