Meeting Abstract

1.5  Jan. 4  Evidence from silk proteins for the single origin of spider orb-webs by the early Cretaceous. GARB, J. E.*; DIMAURO, T.; VO, V.; HAYASHI, C.Y.; University of California, Riverside; University of California, Riverside; University of California, Riverside; University of California, Riverside jessica.garb@ucr.edu

The orb-web is a spectacular evolutionary innovation that enables spiders to capture flying prey. Spiders build their wheel-shaped orb-webs from a suite of silk proteins, which are products of a single gene family. Orb-web construction is characteristic of many species in the superfamilies Deinopoidea and Araneoidea. Though strikingly similar, notable differences between deinopoid and araneoid orb-webs suggest that the orb-web architecture convergently evolved in these two lineages. Yet, cladistic analyses of morphological and behavioral characters indicate that deinopoids and araneoids are sister groups and share a common orb-weaving ancestor. This result implies a unique instance of orb-web evolution, followed by its occasional loss or extreme modification. By constructing and surveying spider silk gland expression (cDNA) libraries, we show that deinopoid and araneoid spiders possess similar silk proteins utilized in orb-web construction. Further, phylogenetic analyses of the spider silk protein family confirm close relationships between deinopoid web-building silks and their araneoid counterparts. Our results indicate that the common ancestor of deinopoids and araneoids possessed the key silk proteins involved in orb-web construction, favoring the hypothesis for the orb-web�s single origin. We can estimate the age of this common ancestor with spider fossils from early Cretaceous amber (~136 million years old). Accordingly, the orb-web�s origin must also minimally date to this period.