Plasticity in extended phenotypes: orb web architectural responses to variations in prey parameters

Abstract

SUMMARYA spider orb web is an extended phenotype; it modifies and interacts with the environment, influencing spider physiology. Orb webs are plastic, responding to variations in prey parameters. Studies attempting to understand how nutrients influence spider orb-web plasticity have been hampered by the inability to decouple prey nutrients from other, highly correlated, prey factors and the intrinsic link between prey protein and prey energy concentration. I analyzed the nutrient concentrations of cockroaches, and adult and juvenile crickets to devise experiments that controlled prey protein concentration while varying prey size, ingested mass, energy concentration and feeding frequency of the orb web spider Argiope keyserlingi. I found that A. keyserlingi alters overall architecture according to feeding frequency. Decoration length was inversely related to ingested prey mass and/or energy density in one experiment but directly related to ingested prey mass in another. These contradictory results suggest that factors not examined in this study have a confounding influence on decoration plasticity. As decorations attract prey as well as predators decreasing decoration investment may, in some instances, be attributable to benefits no longer outweighing the risks. Web area was altered according to feeding frequency, and mesh size altered according to feeding frequency and prey length. The number of radii in orb webs was unaffected by prey parameters. A finite amount of silk can be invested in the orb web, so spiders tradeoff smaller mesh size with larger web capture area, explaining why feeding frequency influenced both web area and mesh size. Mesh size is additionally responsive to prey size via sensory cues, with spiders constructing webs suitable for catching the most common or most profitable prey.

Caught in the web: Spider web architecture affects prey specialization and spider–prey stoichiometric relationships

“…Web architecture differs greatly among spider species, ranging from the commonly known orb construction, to three‐dimensional tangles with crossing lines of silk, such as tangle webs, and those with a dense basal sheet referred to as sheet‐tangle webs (Figure 1) (Savory, 1960). These differences in the architecture of the webs may result in different types of prey being captured (Blamires, 2010; Guevara & Avilés, 2009; Sanders et al., 2015). Although the nutritional content of captured prey is beyond the control of the spider (Mayntz, Raubenheimer, Salomon, Toft, & Simpson, 2005), web architecture likely affects the energy pathways and the stoichiometry of spider–prey interactions via selective capture and feeding (Mayntz, Toft, & Vollrath, 2009; Schmidt et al., 2012).…”

Humidity-mediated changes in an orb spider's glycoprotein adhesive impact prey retention time

“…Both the non-adhesive and adhesive components of orb webs exhibit phenotypic plasticity (Blamires, 2010;Boutry and Blamires, 2013;Dawkins, 1982). Differences in diet and prey type cause striking differences in both a web's architecture and the properties of its threads (Blamires et al, 2016;Herberstein and Tso, 2011;Scharf et al, 2011;Townley et al, 2006;Tso et al, 2007), as can environmental factors such as wind (Wu et al, 2013).…”

Diet-induced covariation between architectural and physicochemical plasticity in an extended phenotype

“…Beaver dams, termite mounds, bee hives, bird nests and spider webs are examples of extended phenotypes that can moderate fitness (Dawkins, 1982;Healy et al, 2008;Blamires, 2010;Bailey, 2012). As plastic responses in extended phenotypes are not measurable at a somatic level, they may go unnoticed as important adaptive responses in variable environments (Plague and McArthur, 2003;Borges, 2008;Blamires, 2010;Bailey, 2012). Thus experiments using suitable model extended phenotypes are urgently required to better understand the adaptive benefits of trait plasticity (Bailey, 2012;Herberstein and Hebets, 2013).…”

“…This is because spiders and their webs fit all of the following criteria: (i) they keep well in laboratory conditions, (ii) they change measurably in response to stimuli over short time periods, (iii) they consist of different correlated architectural features (e.g. radials, capture area, spiral spacing, and decorations/ stabilimenta), and most importantly (iv) there is a broad accumulation of information available regarding the behaviours, physiology, ecology, adaptability and potential trade-offs associated with building webs (Blamires, 2010;Baba et al, 2012;Nakata, 2012;Herberstein and Hebets, 2013;Blamires et al, 2016). Several studies show that a range of web architectural features and silk physicochemical properties co-vary in response to changes in environmental factors such as humidity, ultraviolet (UV) radiation, prey type and nutrients (see reviews by Blackledge et al, 2011;Herberstein and Tso, 2011;Scharf et al, 2011;Boutry and Blamires, 2013).…”

“…The benefit of carefully dissecting the relationship between environmental cues and architectural properties was demonstrated in a study that systematically assessed the influence of diet on multiple web architectural features (Blamires, 2010). In this study, the diet of the orb web spider Argiope keyserlingi Karsch 1878 was manipulated by feeding them different prey types (cockroaches or crickets) or prey of different sizes (adult or juvenile crickets).…”