insect form visino as one potential shaping force of spider web

Insect form visino as one potential shaping force of spider web

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759 INTRODUCTION Studies investigating the evolution of signals are typically concerned with intraspecific communication, such as sexual signals. For example, the signals used in courtship displays are often examined with respect to how habitat physical characteristics (Fleishman, 1992; Marchetti, 1993; Forrest, 1994; Catchpole and Slater, 1995) or receiver preference (Proctor, 1992; Basolo, 1995; Rodd et al., 2002; Witte and Sawka, 2003) affect signal efficacy. Other studies investigate the strategic aspects of signal evolution by examining the constraints on signal intensity or signal honesty (Panhuis and Wikinson, 1999; Grether, 2000; Quillfeldt, 2002; Brandt, 2003; Hunt et al., 2004). While various modes of conspecific selection pressures could drive the evolution of communication signals, selection pressures from other species maybe equally as important. For example, several modalities of signals involved in aposematism or camouflage of certain organisms are known to be significantly shaped by the prey’s major predators (Ruxton et al., 2004). In many communication systems, the signalers and the intended receivers are not the only participants. Frequently there are unintended participants such as various forms of exploiters (Endler, 1993). For example, exploiters may follow a signal to locate the emitter or provide false signals to elicit a stereotypical response from receivers that is favorable to the exploiters (Johnstone, 1997). The latter has been termed ‘code breaking’ (Alcock, 2005) and has been investigated in systems such as brood parasitism (Davis et al., 1998; Kilner et al., 1999), prey courtship signal mimicking (Lioyd, 1975; Haynes et al., 2002) and prey recognition signal exploitation (Thomas et al., 2002). Currently, most relevant studies on these heterospecific sensory exploitations focus on describing the contemporary molecular, physiological or behavioral mechanisms involved. Comparative studies using phylogenetic approaches to investigate how such signals might have evolved are still rare. Furthermore, characteristics of the exploited receiver’s sensory system are likely to shape the evolution of code-breaking signals. However, empirical evidence of how prey sensory systems drive the design and evolution of exploiter signals is still rare. In this study, we assess how prey sensory preference shape the design of luring signals generated by an exploiter by studying the web decorations built by orb-web spiders of the genus Argiope . Decorations are silk structures on webs built by at least 22 genera of orb-web spiders (Herberstein et al., 2000). Most members of the genera Nephila , Cyclosa , Uloborus and Gea build a linear form decoration on their webs (Fig.1A,B). However, species of the genus Argiope decorate their webs with either linear or cruciate forms of decorations (Fig.1C,D). Several hypotheses about the functions of Argiope decorations have been proposed (for reviews, see Herberstein et al., 2000; Bruce, 2006; Théry and Casas, 2009) but many researchers consider spider web decorations as a visual signal that influences the interactions between spiders and prey. One of the proposed functions
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This note was uploaded on 01/27/2012 for the course ECOLOGY 300 taught by Professor Zumdahli during the Spring '11 term at St. Mary NE.

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Insect form visino as one potential shaping force of spider web

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