Dynamic evolution of locomotor performance independent of changes in extended phenotype use in spiders

Many animals utilise self-built structures (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 – with disparate feedbacks on
trait evolution. Here, using brown spiders (Araneae: marronoid clade), 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 (sprint speed)
and leg spination (expression of capture spines on front legs). We found
that in this group high locomotor performance, with running speeds of over
100 body lengths per second, evolved repeatedly – both in web building and
cursorial spiders. There was no correlation with running speed, and leg
spination was only poorly correlated, relative to the use of extended
phenotypes, indicating that web use does not reduce selective pressures on
body functions involved in prey capture and defence per se.
Consequently, extended prey capture devices serve as supplements rather
than substitutions to body traits and may only be beneficial in
conjunction with certain life history traits, explaining the rare
evolution and repeated loss of trapping strategies in predatory animals.