Phylogenetic relationships of the spider family Tetragnathidae (Araneae, Araneoidea) based on morphological and DNA sequence data.

The monophyly of Tetragnathidae including the species composition of the family (e.g., Are Nephila and their relatives part of this lineage?), the phylogenetic relationships of its various lineages, and the exact placement of Tetragnathidae within Araneoidea have been three recalcitrant problems in spider systematics. Most studies on tetragnathid phylogeny have focused on morphological and behavioral data, but little molecular work has been published to date. To address these issues we combine previous morphological and behavioral data with novel molecular data including nuclear ribosomal RNA genes 18S and 28S, mitochondrial ribosomal RNA genes 12S and 16S and protein-coding genes from the mitochondrion [cytochrome c oxidase subunit I (COI)] and from the nucleus (histone H3), totaling ca. 6.3 kb of sequence data per taxon. These data were analyzed using direct optimization and static homology using both parsimony and Bayesian methods. Our results indicate monophyly of Tetragnathidae, Tetragnathinae, Leucauginae, the "Nanometa clade" and the subfamily Metainae, which, with the exception of the later subfamily, received high nodal support. Morphological synapomorphies that support these clades are also discussed. The position of tetragnathids with respect to the rest of the araneoid spiders remains largely unresolved but tetragnathids and nephilids were never recovered as sister taxa. The combined dataset suggests that Nephilidae is sister to Araneidae; furthermore, the sister group of Nephila is the clade composed by Herennia plus Nephilengys and this pattern has clear implications for understanding the comparative biology of the group. Tetragnathidae is most likely sister to some members of the "reduced piriform clade" and nephilids constitute the most-basal lineage of araneids.