Michael B. J. Kelly, Kawsar Khan, Kaja Wierucka, Braxton R. Jones, Ryan Shofner, Shahan Derkarabetian, Jonas Wolff

Many animals utilize self-built structures – so-called extended phenotypes – to enhance body functions, such as thermoregulation, prey capture or defence. Yet, it is unclear whether the evolution of animal constructions supplements or substitutes body functions. Here, using Austral brown spiders, we explored if the evolutionary loss and gain of silken webs as extended prey capture devices correlates with alterations in traits known to play an important role in predatory strikes - locomotor performance and leg spination. For this purpose, we combined the reconstruction of the phylogeny of the Austral marronoid clade of spiders based on UCE target sequence capture with the assembly of kinematic, morphological and ecological data. We found that in this group extreme locomotor performance, with running speeds of over 100 body lengths per second, evolved repeatedly – both in web builders and cursorial spiders. There was no correlation with running speed, and leg spination only poorly correlated, relative to the use of extended phenotypes, with all of these traits showing highly mosaic, independent evolutionary patterns. This indicates that the use of webs does not reduce the selective pressure on body functions involved in prey capture and defence per se.