Tangled in a sparse spider web: single origin of orb weavers and their spinning work unravelled by denser taxonomic sampling

Abstract

In order to study the tempo and the mode of spider orb web evolution and diversification, we conducted a phylogenetic analysis using six genetic markers along with a comprehensive taxon sample. The present analyses are the first to recover the monophyly of orb-weaving spiders based solely on DNA sequence data and an extensive taxon sample. We present the first dated orb weaver phylogeny. Our results suggest that orb weavers appeared by the Middle Triassic and underwent a rapid diversification during the end of the Triassic and Early Jurassic. By the second half of the Jurassic, most of the extant orb-weaving families and web designs were already present. The processes that may have given origin to this diversification of lineages and web architectures are discussed. A combination of biotic factors, such as key innovations in web design and silk composition, as well as abiotic environmental changes, may have played important roles in the diversification of orb weavers. Our analyses also show that increased taxon sampling density in both ingroups and outgroups greatly improves phylogenetic accuracy even when extensive data are missing. This effect is particularly important when addition of character data improves gene overlap.

Figure 1.

ML tree of data matrix dataset1_v1; miniature illustration at bottom left shows the same tree with proportional branch lengths. Bootstrap values of the major lineages are shown above branches. DIP, Dipluridae; AUS, Austrochilidae; PLE, Plectreurideae; SEG, Segestriidae; PAL, Palpimanidae; ERE, Eresidae; HER, Hersiliidae; OEC, Oecobiidae; RTA, RTA clade; DEI, Deinopidae; ULO, Uloboridae; NIC, Nicodamidae; THE, Theridiidae; NES, Nesticidae; ANA, Anapidae; SYM, Symphytognathidae; MIM, Mimetidae; Ark, Arkys (Araneidae); TET, Tetragnathidae; Tro, Trogloneta (Mysmenidae); MAL, Malkaridae; TSD, Theridiosomatidae; MYS, Mysmenidae; NEP, Nephilidae; Oar, Oarcinae; ARA, Araneidae; PIM, Pimoidae; Ste, Stemonyphantes (Linyphiidae); CYA, Cyatholipidae; LIN, Linyphiidae. Taxonomic groups are depicted with different colours; grey is unknown (misidentified as Nesticus sp.; see the electronic supplementary material).

Figure 2.

Chronogram of orb weavers and relatives based on dataset1_v1. Branches are coloured according to the parsimony ancestral reconstruction of web types; pie charts represent probabilities of ancestral states from the Mk1 model of [52]. Node bars show confidence intervals. Taxonomic abbreviations are as in figure 1.