Spider silk is enigmatic, and web structure, design, and adult morphology of the spinning apparatus of spiders once informed how systematists approached the spider phylogeny. The orb-web and adaptation of viscous silk was considered a key innovation leading to rapid diversification of spiders. However, the advent of molecular techniques including recent phylogenomics studies, overturned this major paradigm in spider evolution. Clades once considered monophyletic are no more. The orb-web is not a pinnacle of evolution, and the former sister group, using cribellate silk (loops of fibrils combed from a specialized silk plate on the abdomen), is now sister to the predominately non-silk using RTA clade with a more ancient common orb-web ancestor.
Little work has explored the ontogeny of the spinning apparatus in spiders, but by doing so, one could find empirical support for the paradigm shift in the new Araneae Tree of Life (AToL), such as orb-weaving traits within the RTA clade. To address this, Tengella perfuga, a rare cribellate-silk using member of the RTA clade, was selected for a case study of natural history, including web ontogeny. The full spigot ontogeny of T. perfuga was characterized and compared with previous studies of both orb-weaving and RTA clade members. Using a pooled ontogeny dataset across studies, including lab populations of Hogna carolinensis and Dolomedes tenebrosus, potential drivers of spigot number across spider lineages was explored using the AToL in PGLS analyses.
There were vestiges of orb-weaving behavior within the web spinning of Tengella perfuga, and a trio of silk spigots that may be homologous with the trio of viscous orb-weavers. PGLS analyses of female and second instar spigot data, resulted in maximum number of instars, foraging strategy and variety of spigots possessed significantly correlated to specific spigot numbers. An ancestral character estimation analysis performed on the unique spigots, such as the trio, found some preliminary evidence for, but not confirming, homology. This study utilized novel techniques to explore spider silk use evolution. With deeper taxon sampling and improved statistical methods allowing the full ontogeny to be included in PGLS analyses, a better understanding of silk use evolution will emerge.
Spiders, silk, spigot, natural history, evolution, comparative biology
Level of Degree
UNM Biology Department
First Committee Member (Chair)
Second Committee Member
Third Committee Member
Fourth Committee Member
Fifth Committee Member
Alfaro, Rachael. "Novel Approaches to Exploring Silk Use Evolution in Spiders." (2017). https://digitalrepository.unm.edu/biol_etds/201
Raw spigot ontogeny data for Tengella perfuga
Preening.wmv (1604 kB)
Step 1: Male preening behavior
Strumming compress.wmv (10272 kB)
Step 2: Strumming, stroking, stilting
Bridal Veil compress.wmv (9216 kB)
Step 3: Bridal veil
Copulation compress.wmv (2593 kB)
Step 4: Copulation
Success compress.wmv (10207 kB)
Successful courtship sequence