­Comparative spigot ontogeny across the spider tree of life

Abstract

Spiders are well known for their silk and its varying use across taxa. Very few studies have examined the silk spigot ontogeny of the entire spinning field of a spider. Historically the spider phylogeny was based on morphological data and behavioral data associated with silk. Recent phylogenomics studies have shifted major paradigms in our understanding of silk use evolution, reordering phylogenetic relationships that were once thought to be monophyletic. Considering this, we explored spigot ontogeny in 22 species, including Dolomedes tenebrosus and Hogna carolinensis, reported here for the first time. This is the first study of its kind and the first to incorporate the Araneae Tree of Life. After rigorous testing for phylogenetic signal and model fit, we performed 60 phylogenetic generalized least squares analyses on adult female and second instar spigot morphology. Six analyses had significant correlation coefficients, suggesting that instar, strategy, and spigot variety are good predictors of spigot number in spiders, after correcting for bias of shared evolutionary history. We performed ancestral character estimation of singular, fiber producing spigots on the posterior lateral spinneret whose potential homology has long been debated. We found that the ancestral root of our phylogram of 22 species, with the addition of five additional cribellate and ecribellate lineages, was more likely to have either none or a modified spigot rather than a pseudoflagelliform gland spigot or a flagelliform spigot. This spigot ontogeny approach is novel and we can build on our efforts from this study by growing the dataset to include deeper taxon sampling and working towards the capability to incorporate full ontogeny in the analysis.

Evolution of aerial spider webs coincided with repeated structural optimization of silk anchorages

“…For spinning apparatus state, we fitted an Equal Rates model (ER), an All Rates Different model (ARD) and a customized model with suppressed state 1 to 2 transitions (following Dollo's law, see (Alfaro et al. )), of which the Dollo's law model had the strongest support ( AICcw = 0.640). For web type, ER, SYM, and ARD models were fitted, of which the ER model was preferred ( AICcw = 0.583).…”

Silk genes and silk gene expression in the spider Tengella perfuga (Zoropsidae), including a potential cribellar spidroin (CrSp)

“…From these spigots, the largest spigot is called the “modified spigot,” and it is flanked by two smaller spigots. This spigot trio has been designated the MS-FL triad, or “modified spigot with flankers” triad by Alfaro et al [ 27 , 28 ]. The arrangement of the MS-FL spigots is quite similar to the spigot triad found in araneoids.…”

The ontogeny of the spinning apparatus of Tengella perfuga (Araneae: Zoropsidae)

“…A phylogenetic comparative analysis using the spider tree of life and a large dataset of spigot ontogeny data for 22 species from 13 families explores evolutionary trends in silk use (Alfaro et al. ).…”

“…These comparisons deserve further exploration within a phylogenetic framework (Alfaro et al. ), now available with the spider tree of life (Wheeler et al. ).…”