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Unformatted text preview: Work, R . W. 1981 . A comparative study of the supercontraction of major ampullate silk fibers of orb-web-building spiders (Araneae). J. Arachnol ., 9:299-308 . A COMPARATIVE STUDY OF THE SUPERCONTRACTIO N OF MAJOR AMPULLATE SILK FIBERS OF ORB-WEB-BUILDING SPIDERS (ARANEAE)t Robert W . Work Fiber and Polymer Science Program, David Clark Laboratory North Carolina State University, Raleigh, North Carolina, 27607 U .S.A. ABSTRACT An improved and simple technique is described for determining the magnitude of the recentl y observed phenomenon of supercontraction of major ampullate silk fibers of orb-web-building spiders . Supercontraction ratios obtained by the use of that method and also from an instrumental method ar e given. It is seen that only three levels of supercontraction are found among twenty two species o f orb-web-building spiders . The data are presented on the basis of taxonomic classification and ar e subjected to statistical analyses in order to determine which ones may be effectively differentiate d from the others . A contribution to the integerity of the wetted web is suggested as a function for the retractive driving force which underlies supercontraction. Mention is made of the possible usefulnes s of supercontraction as a taxonomic symptom . INTRODUCTION This paper is one of a continuing series (Work 1976, 1977a, 1977b, 1978, 1981) whic h have been concerned with the silks produced by orb-web-building spiders . In the third o f these, the discovery was announced of a very large axial shrinkage in water at roo m temperature of major ampullate silk fibers and its absence in minor ampullate fibers . It had been observed that the former retract to about one half their original lengths when they are wetted in an axially unrestrained condition . In the field of macromolecular chemistry this phenomenon is not unknown, being termed supercontraction . But it was quite unexpected, for although it can be induced in some natural and man-made fibers, i t can be produced only under drastic conditions of chemical swelling or elevated tempera - tures, or both . Thus its existence has encouraged an expanded physico-chemical investi - gation, having as its objectives the characterization of the phenomenon and the determi- nation of its basis at the molecular level . It is expected that the fruits of this research wil l be published in future papers of this series . But since orb webs are commonly wetted b y dew and rain, arachnological considerations were not disregarded . 'Grants from the Research Corporation and the National Science Foundation (currently CPE- 79-08905) supported, in part, the research described in this paper . 300 THE JOURNAL OF ARACHNOLOG Y In the earlier part of the study it was found that the magnitude of supercontractio n was remarkably uniform among all of the samples examined, as compared with thei r other physical properties such as axial force-elongation behavior . When one spider was found to have produced silk having an entirely different level of supercontraction, th...
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