Feeding mediated web-building plasticity in a cobweb spider

Behavioral plasticity has been proposed as a means by which animals alter their phenotypes in response to changing conditions. Animals may display behavioral plasticity as a consequence of environmental variation. The detritus-based, bell-shaped cobweb spider Campanicola campanulata is an ideal model to study behavioral plasticity, because its web architecture is easy to be quantified, and the functions of different parts of the web are clear. Though the plasticity of cobweb architecture has been reported in a few species, retreats as important defensive structures have rarely been considered before because retreats in most cobwebs are relatively small compared with the web size. We studied the web-building behaviors of C. campanulata under different feeding regimes. We set up 3 spider treatments with different feeding conditions: marginally well fed, moderately well fed, and extremely well fed, and observed the differences in the web architecture among them. In addition, we measured the mechanical properties of anchor silk, and also calculated the foraging and defense investment of the spiders. The results showed that marginally well-fed spiders build cobwebs with significantly longer length of anchor silk, lower retreat to the ground, more number and longer gumfooted lines, and larger capture area, while extremely well-fed spiders build cobwebs with significantly bigger retreat volume and higher height of retreat to the ground. In addition, marginally well-fed spiders invest significantly less during cobweb construction. However, there was no significant difference between the breaking force and elongation at break in anchor silk among different treatments. These results demonstrated that marginally well-fed spiders invest more in foraging, and extremely well-fed spiders invest more in defense, and the spider made a balance between foraging and predator avoidance in response to changes in physiological state. Our study strengthens the current understanding of web construction in cobweb spiders, especially those facing high costs during retreat construction.