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Evarcha culicivora (Araneae, Salticidae) feeds indirectly on vertebrate blood by choosing, as preferred prey, bloodcarrying female mosquitoes. Mutual mate-choice behavior is also pronounced in this species. Here we show that, when E. culicivora feeds indirectly on blood, it acquires a diet-related odor that makes it more attractive to the opposite sex. The mate-choice decisions of the adults of both sexes were investigated in a series of experiments based on comparing how long the test spider remained close to the odor of one source spider on one day and to the odor of a different source spider on the following day. Four different maintenance diets for source spiders were used in these experiments: bloodfed female mosquitoes (Culicidae, Anopheles gambiae ss), sugar-fed female mosquitoes, male mosquitoes, and lake flies (Chironomidae, Nilodorum brevibucca). Both sexes of E. culicivora spent more time close to the odor of opposite-sex conspecifics that had been on a diet of bloodfed mosquitoes (blood diet) instead of any of the three nonblood diets. Opposite-sex conspecifics that had been on a nonblood diet became more attractive once they were switched to a blood diet. That the attractive odor from blood dissipates was shown when spiders became less attractive once they were switched to a nonblood diet or subjected to a fast. However, there was no evident preference for the odor of a same-sex conspecific on a blood diet instead of a lake fly diet. These findings are discussed in the context of sexual selection and sensory exploitation. mosquitoes | olfaction | predation | sensory exploitation | sexual selection www.pnas.org/cgi/doi/10.1073/pnas.0904125106

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2009.04.005 Byline: Ximena J. Nelson (a)(b), Robert R. Jackson (a)(c) Abstract: Many predators are averse to attacking ants and many palatable arthropods are Batesian mimics of ants. We considered whether aggregating Batesian mimics of ants can become more repelling to ant-averse predators by, as a group, resembling groups of ants (collective mimicry). Myrmarachne melanotarsa is a gregarious ant-like jumping spider (Salticidae) that resembles and associates with the ant Crematogaster sp. We used three large ant-averse salticids as predators in experiments. Besides M. melanotarsa and Crematogaster we used midges (Chaoborus sp.) and a small nonant-like, but gregarious, salticid (Menemerus sp.) as prey. The predators readily attacked both live midges and the nonant-like salticids that were presented singly or in groups but rarely attacked ants or ant mimics. Predators attacked ants and ant mimics presented in groups less often than they attacked solitary ants and ant mimics. In another experiment, motionless lures (groups of arthropods mounted in lifelike posture) were used. The findings showed that, independent of prey behaviour and movement, the predators were averse to being in close proximity to groups of ants and ant mimics, but had no evident aversion to the close proximity of groups of nonant-like salticids. Palatability tests demonstrated that the predators fed for long periods on M. melanotarsa, Menemerus and Chaoborus, but released Crematogaster almost immediately. Our results suggest that these predators have an innate aversion to ants and ant mimics and also that they are innately predisposed to perceive a group of ants (or ant mimics) as more repelling than solitary ants or ant mimics. Author Affiliation: (a) School of Biological Sciences, University of Canterbury, New Zealand (b) Centre for the Integrative Study of Animal Behaviour, Macquarie University, Australia (c) International Centre of Insect Physiology and Ecology (ICIPE), Thomas Odhiambo Campus, Kenya Article History: Received 29 October 2008; Revised 22 December 2008; Accepted 7 April 2009 Article Note: (miscellaneous) MS. number: 08-00706R