NIKOLAJ SCHARFF
Project description
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(this project is done in collaboration withTodd Blackledge from the University of Akron, Akron, USA and John W. Wenzel from Ohio State University, Columbus, USA)
The spider family Araneidae is the largest family of spiders that construct orb-webs (wheel-shaped two-dimensional webs). Yet, many araneids have evolved highly specialized web construction behaviors that result in webs unlike typical orb webs. We are currently working to establish a generic level phylogeny for relationships within this group to investigate how and why these behavioral specializations have evolved, how they contribute to the dominance of araneid spiders as predators of flying insects, and how evolution of behavior and silk biomechanics interact with one another. This project includes molecular data from multiple nuclear and mitocondrial loci, as well as morphological data. Todd Blackledge and John Wenzel are responsible for the molecular and biomechanical aspects of the project. Nikolaj Scharff is responsible for the morphological aspects and together they will analyze the combined data.
PROJECT OBJECTIVES:
1) To establish a generic level phylogeny for the family Araneidae: The Araneidae includes more than 2800 described species of orb-weaving spiders and is distinguished from other orb weaving families by its immense ecological diversity. To date, there has been only a single phylogenetic analysis of the Araneidae (Scharff & Coddington, 1997). Scharff and Coddington used morphological and behavioral characters to produce a working araneid phylogenetic hypothesis, but they concluded that their matrix contained too many taxa and too few characters such that many relationships were poorly resolved. The Scharff & Coddington phylogeny has been used in over 50 studies. Therefore, there is a need to expand character sampling to provide for robust relationships for this often-studied group of spiders. Our study will provide a robustly supported phylogeny for araneid relationships by producing the first molecular data sets and expanding the sampling of morphological and behavioral characters.
2) To investigate the phenotypic evolution of spider silks: The evolutionary demands of prey capture under a variety of different ecological conditions is expected to act upon the mechanical properties of the silks that spiders use to construct orb webs. Only a tiny fraction of the different silks spun by spiders have been mechanically tested. Moreover, the silks that have been characterized mechanically are spun primarily by two species of spiders, Araneus diadematus (Araneidae) and Nephila clavipes (Tetragnathidae), because these spiders are conspicuous, large, and abundant. We will measure the material properties of the frame and capture silk fibers spun by an ecologically diverse set of araneids. We will then use our phylogenetic hypothesis from Objective 1 to evaluate the role of coevolution of silk biomechanical phenotypes with web architectures and spider size.
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