Novel Approaches to Exploring Silk Use Evolution in Spiders

Author

Rachael Alfaro, University of New MexicoFollow

Publication Date

Spring 4-14-2017

Abstract

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.

Language

English

Keywords

Spiders, silk, spigot, natural history, evolution, comparative biology

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

Kelly Miller

Second Committee Member

Charles Griswold

Third Committee Member

Christopher Witt

Fourth Committee Member

Joseph Cook

Fifth Committee Member

Boris Kondratieff

Recommended Citation

Alfaro, Rachael. "Novel Approaches to Exploring Silk Use Evolution in Spiders." (2017). https://digitalrepository.unm.edu/biol_etds/201