Caught In a Sticky Situation:The Orb-Weaving SpiderwebEmily Gastelum and Taylor StinchcombBiology 342 Fall 2011 |
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What is Ontogeny?Ontogeny describes how a behavior changes over the course of the animal’s lifetime. It often examines the roles of social and environmental conditions in the development of behavior, and how the underlying machinery of behavior—such as gene expression, neurocircuitry, hormonal pathways, and morphology—change in response to varying environmental conditions. Web Building is InnateThe basic motor patterns involved in construction of the orb web are largely stereotypical within phylogenetic clades of orb weaving spider families, resulting in species-specific differences in web architecture (Blackledge, et. al, 2011). This suggests that there is a genetic basis for web-building behavior in these spiders, or rather that the behavior is innate. Spider hatchlings raised in the absence of adults were observed to initially lay silk in no clear structure, but after one month, the young spiders constructed webs showing features characteristic of the adult webs of their species (Witt, et al, 1972), supporting the hypothesis that the basic web building behavior is internal to the spider and does not have to be learned. Changes in the Orb Web as Spiders AgeAs a spider develops from juvenile to adult, the web that it builds grows in overall size and the size of the mesh becomes wider with greater spacing among threads. While the size of the web is correlated to a spider’s weight, the regularity in thread spacing is related to spider maturity. Because the weight of female spiders does not change after they reach maturity and produce eggs, the size of the web no longer needs to change to hold a greater mass. With further aging, the web texture becomes increasingly coarse with irregular spacing until the spider’s final molt (Witt, et. al, 1972). There is no evidence that silk production varies with spider age, but larger spiders have been found to include a greater volume of silk in their webs. The figure to the right shows (a) that the overall stopping potential of the web increased isometrically (proportionally) with spider size even though (b) the stickiness per capture area increased at a rate lower than is predicted by isometry (isometry is indicated by the dashed regression line). The ability of the web to stop and retain prey is improved by larger spiders packing more silk into into their webs as well as tougher and more flexible silk threads. The results of this study suggest that by concentrating their silk resources, adult spiders are able to target larger and faster-flying prey (Sensenig, et. al, 2011).
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