Correlated evolution between coloration and ambush site in predators with visual prey lures

The evolution of a visual signal will be affected by signaler and receiver behavior, and by the physical properties of the environment where the signal is displayed. Crab spiders are typical sit-and-wait predators found in diverse ambush sites, such as tree bark, foliage, and flowers. Some of the flower-dweller species present a UV-white visual lure that makes them conspicuous and attractive to their prey. We hypothesized that UV-white coloration was associated with the evolution of a flower-dwelling habit. In addition, following up on results from a previous study we tested whether the UV-white coloration evolved predominantly in flower-dwelling species occurring in Australia. We measured the reflectance of 1149 specimens from 66 species collected in Australia and Europe, reconstructed a crab spider phylogeny, and applied phylogenetic comparative methods to test our hypotheses. We found that the flower-dwelling habit evolved independently multiple times, and that this trait was correlated with the evolution of the UV-white coloration. However, outside Australia non-flower-dwelling crab spiders also express a UV-white coloration. Therefore, UV-white reflectance is probably a recurring adaptation of some flower dwellers for attracting pollinators, although it may have other functions in non-flower dwellers, such as camouflage.

We would like to thank A. L. Llandres, F. G. Gonzalvez, E. de Mas, M. Amboni, D. P. Decanini, and S. van Broekhoven for helping to collect and measure spiders; C. Urones and D. Logunov for assisting in spiders taxonomical identification; K. Umbers for guidance on the DNA extractions and PCR's; and Macquarie University and project CGL2015-71396-P for financial support. The authors declare no conflict of interests.

Peer reviewed