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doi: 10.1098/rspb.2010.0729 , 3019-3025 first published online 12 May 2010 277 2010 Proc. R. Soc. B Kensuke Nakata and Samuel Zschokke Cyclosa asymmetry, spider orientation and running speed in Upside-down spiders build upside-down orb webs: web References http://rspb.royalsocietypublishing.org/content/277/1696/3019.full.html#ref-list-1 This article cites 30 articles, 3 of which can be accessed free Subject collections (1875 articles) ecology (153 articles) biomechanics (1568 articles) behaviour Articles on similar topics can be found in the following collections Email alerting service here right-hand corner of the article or click Receive free email alerts when new articles cite this article - sign up in the box at the top http://rspb.royalsocietypublishing.org/subscriptions go to: Proc. R. Soc. B To subscribe to This journal is © 2010 The Royal Society on November 7, 2010 rspb.royalsocietypublishing.org Downloaded from
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Upside-down spiders build upside-down orb webs: web asymmetry, spider orientation and running speed in Cyclosa Kensuke Nakata 1, * , and Samuel Zschokke 2 1 Faculty of Human Environment, Nagasaki Institute of Applied Science, Nagasaki, Japan 2 Section of Conservation Biology ( NLU ) , Department of Integrative Biology, University of Basel, Basel, Switzerland Almost all spiders building vertical orb webs face downwards when sitting on the hubs of their webs, and their webs exhibit an up–down size asymmetry, with the lower part of the capture area being larger than the upper. However, spiders of the genus Cyclosa , which all build vertical orb webs, exhibit inter- and intraspecific variation in orientation. In particular, Cyclosa ginnaga and C. argenteoalba always face upwards, and C. octotuberculata always face downwards, whereas some C. confusa face upwards and others face downwards or even sideways. These spiders provide a unique opportunity to examine why most spiders face downwards and have asymmetrical webs. We found that upward-facing spiders had upside-down webs with larger upper parts, downward-facing spiders had normal webs with larger lower parts and sideways-facing spiders had more symmetrical webs. Downward-facing C. confusa spiders were larger than upward- and sideways-facing individuals. We also found that during prey attacks, down- ward-facing spiders ran significantly faster downwards than upwards, which was not the case in upward- facing spiders. These results suggest that the spider’s orientation at the hub and web asymmetry enhance its foraging efficiency by minimizing the time to reach prey trapped in the web. Keywords: foraging efficiency; biomechanics; orientation; web asymmetry; gravity; hub displacement 1. INTRODUCTION Animals in various taxa build some kind of nest. Nests are built to protect the owner from predators, moderate harsh environmental conditions, trap food for consumption or attract females to mate ( Hansell 2005 ). Ecological fac- tors, together with the way the owner animal uses the nest, affect the design and the structure of animal-built structures. Among them, the spider’s vertical orb web is a network of silken threads used as a trap.
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