Masters of puppets: could the ecdysteroid route be a common pathway for behavioural manipulation in spiders by different parasites?

Abstract Certain parasites improve their fitness by manipulating their host’s behaviour. Some evidence suggests that parasites exploit innate pathways in the host to manipulate their behaviour. Furthermore, phylogenetically unrelated parasites can generate similar behavioural changes in hosts from the same taxonomic group. Spiders are hosts for several parasites that appear to induce behavioural changes, such as building modified webs that may benefit the parasites. Additionally, some observations on spiders parasitized by Ichneumonidae wasps suggest that the construction of modified webs may merely result from activating the innate ecdysis process. Considering that different parasites may use similar manipulation pathways, we review and examine evidence in the literature that phylogenetically distant parasites (wasps, dipterans, and fungi) may converge on the manipulation mechanism of host spiders through activation of the preexisting mechanism of ecdysis. Also, we suggest that webs built by fungus-infected spiders represent an extended phenotype of these parasites. We conclude that the strategy of behavioural manipulation through activation of innate ecdysis in hosts may have converged in the different spider parasites, which have been favoured over evolutionary time. Therefore, we propose possible pathways for activating this mechanism, and provisions for future investigations to test these hypotheses.