Evolution of spider- and ant-eating habits in crab spiders (Araneae: Thomisidae)

Spiders and ants are infrequent types of prey in the diet of spiders. Both spider- and ant-eating were found in thomisid (crab) spiders but their origin remains unclear. Our goal was to gather data on spider- and ant-eating habits in thomisid spiders, construct a family-level phylogeny, and estimate when these habits evolved. Using prey acceptance experiments, we found 21 spider- and 18 ant-eating genera; based on photographic evidence there were 14 spider- and 20 ant-eating genera; and based on literature there were six spider- and seven ant-eating genera. Altogether we found evidence for 28 spider- and 30 ant-eating genera. We performed the most extensive molecular phylogenetic analysis of Thomisidae to date, using representatives of 75 nominal genera. The resulting topology was congruent with previous studies: Thomisidae were shown to be monophyletic; the genus Borboropactus was identified as a sister group to the remaining thomisids; the current subfamilies emerged as para- or polyphyletic, and Aphantochilinae was monophyletic and rendered Strophiinae paraphyletic within the ‘Thomisus clade’. Ancestral state reconstruction estimated both spider- and ant-eating as ancestral states, suggesting that common ancestors of Thomisidae were euryphagous predators that included spiders but also ants in their diet.