Web forms and the phylogeny of theridiid spiders (Araneae: Theridiidae): Chaos from order

We trace the evolution of the web designs of spiders in the large family Theridiidae using two recent, largely concordant phylogenies that are based on morphology and molecules. We use previous information on the webs of 88 species and new data on the web designs of 78 additional theridiid species (representing nearly half of the theridiid genera), and 12 other species in related families. Two strong, surprising patterns emerged: substantial within‐taxon diversity; and frequent convergence in different taxa. These patterns are unusual: these web traits converged more frequently than the morphological traits of this same family, than the web traits in the related orb‐weaving families Araneidae and Nephilidae, and than behavioural traits in general. The effects of intraspecific behavioural ‘imprecision’ on the appearance of new traits offer a possible explanation for this unusual evolutionary plasticity of theridiid web designs.