Evol Ecol Res 13: 513-526 (2011)     Full PDF if your library subscribes.

Running performance as a function of body size, leg length, and angle of incline in male orb-web spiders, Argiope aurantia

Matthias W. Foellmer1,2, Michael Marson2 and Jordi Moya-Laraño3*

1Department of Biology, Adelphi University, Garden City, New York, USA,  2Department of Biology, Trent University, Peterborough, Ontario, Canada and  3Cantabrian Institute of Biodiversity (ICAB), Departamento de Organismos y Sistemas, Universidad de Oviedo, Oviedo, Spain

Correspondence: M.W. Foellmer, Adelphi University, 1 South Ave., Garden City, NY 11530, USA.
e-mail: foellmer@adelphi.edu


Background: The locomotor performance of various taxonomically distinct species depends on context-specific selection pressures. Superior locomotor performance presumably promotes male mate search success. Running performance on vertical structures is especially important in non-flying species, such as many spiders, because males navigate through high vegetation to find females. Yet recent empirical tests of the relationships of morphological traits, running performance, and angle of incline in spiders have been inconclusive.

Hypothesis: Achievable running speed of male orb-web spiders (Argiope aurantia; Araneidae) on vertical structures is moulded by natural selection on their morphology and locomotor performance. We predict that male body size and leg dimensions are positively related to running speed (in accordance with the recently proposed curvilinear gravity hypothesis) and that if past selection reflects adaptation to run on vertical surfaces, males run faster at steeper angles than on horizontal surfaces.

Methods: We conducted running performance trials in males of A. aurantia. The same males were used at five different incline angles: 0°, 22.5°, 45°, 67.5°, and 90°.

Results: Spider leg dimensions are strongly correlated with body size. Larger males ran faster at all incline angles. Independent of morphology, males tended to run faster at steeper inclines than on horizontal surfaces.

Keywords: body size evolution, morphology, orb-web spiders, running speed, sex-specific selection, sexual dimorphism.

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