Evolution of hyperflexible joints in sticky prey capture appendages of harvestmen (Arachnida, Opiliones)

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• 作者：Jonas O. Wolff ; Jochen Martens ; Axel L. Schönhofer…
• 关键词：Prey capture ; Adhesion ; Predator ; prey interaction ; Biomechanics ; Torsion ; Kinematics ; Arachnida ; Soil communities
• 刊名：Organisms Diversity & Evolution
• 出版年：2016
• 出版时间：September 2016
• 年：2016
• 卷：16
• 期：3
• 页码：549-557
• 全文大小：2,599 KB
• 刊物主题：Biodiversity; Evolutionary Biology; Developmental Biology; Animal Systematics/Taxonomy/Biogeography; Plant Systematics/Taxonomy/Biogeography;
• 出版者：Springer Berlin Heidelberg
• ISSN：1618-1077
• 卷排序：16

文摘

The rigid leg segments of arthropods are flexibly connected by joints, which usually consist of two ball-and-bowl hinges, permitting a uniaxial pivoting up to 140°. Here, we report the occurrence of hyperflexible joints (range of movements = 160–200°) in the pedipalps (second pair of appendages) of some harvestmen (Sabaconidae and Nemastomatidae), representing some of the most flexible leg joints among arthropods. Hyperflexion is achieved by a reduction of hinges and a strong constriction of the joint region. We demonstrate that hyperflexion occurs during prey capture and is used to clamp appendages of the prey, in addition to attachment by glue secreted by specialized setae. By means of high-speed video recordings, we found that in the Sabaconidae the tibiotarsal joint of the pedipalp can flex extremely rapidly (<5 ms), limiting prey escape. This is the fastest reported predatory strike in arachnids and caused both by leverage and a click mechanism. By comparative analysis of different related taxa, we retraced joint evolution and found that hyperflexion has independently evolved in Sabaconidae and Nemastomatidae, with totally different joint kinematics. We hypothesize that (rapid) hyperflexion evolved to enhance the efficiency of the pedipalp as a means of prey capture, because in springtails detachable scales limit the action of the sticky secretion of pedipalpal setae.