John Wiley & Sons, Inc.
Silk spinning defines the morphologically constrained embiopterans. All individuals spin for protection, including immatures, adult males and the wingless females. Enlarged front tarsi are packed with silk glands and clothed with ejectors. They spin by stepping with their front feet and releasing silk against substrates and onto preexisting silk, often cloth-like. Spinning is stereotypical and appears to differ between species in frequency and probability of transition between two spin-step positions. This spinning choreography was assessed using thousands of spin-steps scored in the laboratory for 22 species to test: (1) the body size hypothesis predicting that spinning would be more complex for larger species; and (2) the phylogeny hypothesis which predicted that spinning would display phylogenetic signal. Tests relied on published phylogenies for the order Embioptera. Independent contrast analysis revealed relationships between five spin characteristics and body size, whereby, for example, larger webspinners invested in relatively larger prothoracic tarsi used for spinning and in spin-steps that would yield expansive silk coverings. Spin-step dynamics displayed a phylogenetic signal for the frequency of six spin-steps and for 16 spin-step transitions. Discussion focuses on patterns revealed by analysis of phylogenetic signal and the relationship to life style and to recently discovered chemical characteristics of silk.
McMillan, D., K. Hohu, J. S. Edgerly. 17 Feb 2016. Choreography of silk spinning by webspinners (Insecta: Embioptera) reflects lifestyle and hints at phylogeny. Biological Journal of the Linnean Society. DOI:10.1111/bij.12749
Figure S1. Time spent spinning in the two different arenas (Burrow or Chamber) used to record silk spinning behaviour. The graphics across the top indicate the lifestyle of the species named along the horizontal axis in order from left to right. Means are typically based on five or fewer females (see Supporting Information, Table S2 for sample sizes per species). Some species were recorded in only one arena type, as discussed in Methods. Those species that tend toward arboreal lifestyles were prone to spend more time spinning in the bark-lined chamber in contrast with leaf litter or subterranean species, which tended to spend more time spinning when in the burrow arena.
bij12749-sup-0002-TableS1.pdf (1131 kB)
Table S1. Habitat information, sizes, and details of spinning behaviours for embiopteran species videotaped for 1 h sessions in artificial arenas in the laboratory.
bij12749-sup-0003-TableS2.xlsx (43 kB)
Table S2. Results of tests for phylogenetic signal and independent contrast values for behavioural data related to silk spinning behaviour in embiopterans. Bold-faced font = Blomberg's K > 0.7. * = Based on Figure 4 in Miller et al., 2012. ** = Based on figure 3 in Miller et al. (2012).