The Effect of Wind Exposure on the Web Characteristics of a Tetragnathid Orb Spider

Journal of Insect Behavior, May 2017

Studies on spiders in their natural habitats are necessary for determining the full range of plasticity in their web-building behaviour. Plasticity in web design is hypothesised to be important for spiders building in habitats where environmental conditions cause considerable web damage. Here we compared web characteristics of the orb spider Metellina mengei (Araneae, Tetragnathidae) in two different forest habitats differing in their wind exposure. We found a notable lack of differences in web geometry, orientation and inclination between webs built along an exposed forest edge and those built inside the forest, despite marked differences in wind speed. This suggests that M. mengei did not exhibit web-building plasticity in response to wind in the field, contrasting with the findings of laboratory studies on other species of orb spiders. Instead, differences in prey capture and wind damage trade-offs between habitats may provide an explanation for our results, indicating that different species employ different strategies to cope with environmental constraints.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1007%2Fs10905-017-9618-0.pdf

The Effect of Wind Exposure on the Web Characteristics of a Tetragnathid Orb Spider

The Effect of Wind Exposure on the Web Characteristics of a Tetragnathid Orb Spider Nicholas Tew 0 1 Thomas Hesselberg 0 1 0 Department of Life Sciences, Imperial College London , Buckhurst Road, Ascot SL5 7PY , UK 1 Department of Zoology, University of Oxford , South Parks Road, Oxford OX1 3PS , UK Studies on spiders in their natural habitats are necessary for determining the full range of plasticity in their web-building behaviour. Plasticity in web design is hypothesised to be important for spiders building in habitats where environmental conditions cause considerable web damage. Here we compared web characteristics of the orb spider Metellina mengei (Araneae, Tetragnathidae) in two different forest habitats differing in their wind exposure. We found a notable lack of differences in web geometry, orientation and inclination between webs built along an exposed forest edge and those built inside the forest, despite marked differences in wind speed. This suggests that M. mengei did not exhibit web-building plasticity in response to wind in the field, contrasting with the findings of laboratory studies on other species of orb spiders. Instead, differences in prey capture and wind damage trade-offs between habitats may provide an explanation for our results, indicating that different species employ different strategies to cope with environmental constraints. - Spiders face a crucial trade-off in their web-building behaviour between maximising prey capture and minimising energetic expenditure (Higgins 1995). Webs are intrinsically expensive to build, incurring costs associated with metabolism, silk production, time and predation risk (Peakall and Witt 1976; Prestwich 1977; Tanaka 1989; Pasquet et al. 1999). Web damage can impose a large fitness cost on spiders due to both reduced prey capture and the extra cost of repair or rebuilding behaviours (Chmiel et al. 2000; Wherry and Elwood 2009; Tew et al. 2015). Damage can result from a number of factors, including prey impact, larger non-prey animals, wind, rain and falling debris (Craig 1989; Chmiel et al. 2000; Walter and Elgar 2011). Wind, in particular, is known to be a major cause of web damage (Craig 1989), imposing relatively large aerodynamic drag forces which can cause radial and anchor threads to break and result in the partial collapse of the web (Lin et al. 1995; Zaera et al. 2014). Orb spiders generally show a large degree of plasticity in their web design in response to habitat structure and size (Vollrath et al. 1997; Barrantes and Eberhard 2012; Hesselberg 2013), available prey (Schneider and Vollrath 1998; Venner et al. 2000; Blamires 2010) and environmental variables (Vollrath et al. 1997). Hence it is no surprise that several studies have found that spiders change their webs in response to wind. Laboratory studies on two species of the family Araneidae, Araneus diadematus (Hieber 1984; Vollrath et al. 1997) and Cyclosa mulmeinensis (Liao et al. 2009; Wu et al. 2013), have shown a reduction in web capture area when exposed to wind. A comparative field study of Cyclosa ginnaga and C. mulmeinensis revealed that much smaller webs were built by C. mulmeinensis, which inhabited windier environments (Liao et al. 2009). Reducing the area of the capture spiral appears to be an adaptation to windy conditions, presenting a lower surface area to the wind and producing a web that is more resistant to aerodynamic drag (Zaera et al. 2014). The spacing, material properties and tension of silk threads are also influenced by wind. Orb webs built after exposure to artificial wind contained threads with larger spacing, higher tension and higher tensile strength (Vollrath et al. 1997; Liao et al. 2009; Wu et al. 2013). In the comparative field study of Cyclosa spp., the species living in windier conditions, C. mulmeinensis, built webs of thicker, stronger and fewer radial threads, which also differed in terms of their amino acid composition (Liao et al. 2009). Webs with greater spacing in the capture spiral will sag less, with sticky threads being less likely to adhere to each other in windy conditions (Liao et al. 2009; Zaera et al. 2014). Similarly, we might expect that the angle an orb web faces will have a bearing on wind-induced damages. There is some evidence that orb spiders orient webs parallel to the wind direction in both the laboratory (Hieber 1984) and the field (Schoener and Toft 1983; Ramirez et al. 2003). Building webs parallel to the wind, facing it side-on, allows spiders to minimise the surface area of the web that is exposed, and so reduces the potential for web damage. It has also been proposed that the inclination of an orb web, relative to the horizontal, is a feature that might be modified in response to wind (Eberhard 1971). A more horizontal web will face the wind at an angle that is closer to being side-on, and thus will have a lower surface area exposed. Studies on orb spiders that naturally construct vertical webs have not found ev (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1007%2Fs10905-017-9618-0.pdf

Nicholas Tew, Thomas Hesselberg. The Effect of Wind Exposure on the Web Characteristics of a Tetragnathid Orb Spider, Journal of Insect Behavior, 2017, pp. 273-286, Volume 30, Issue 3, DOI: 10.1007/s10905-017-9618-0