Aggressive chemical mimicry of prey pheromones

Mastophora hutchinsoni, a bolas spider

Evolutionary specialization of a predator on a few prey species has potential advantages and disadvantages. Such a predator can evolve to become highly efficient at finding, handling, and utilizing its prey, but the predator becomes dependent on availability of these particular prey, which could be costly in years of prey scarcity. The bolas spider Mastophora hutchinsoni is an extremely specialized predator. The adult female emits chemical attractants that mimic the sex pheromones of its moth prey, a form of aggressive chemical mimicry. The spider exploits the inherent mate-finding behavior of its victims, which are male moths. Two moth species, one active early at night and the other late at night, account for more than 90% of this predator's prey; only two other moth species are ever captured. When prey approach the spider, it strikes them with a sticky ball at the end of a short thread. This capture device, called a bolas, represents a highly reduced web that the spider swings with one of its forelegs. To attract mates, female moths of the two principal prey species release blends of chemical compounds that do not overlap in their components. The spider could produce a master blend of all these components, but preliminary results indicate this would make the attractant much less efficient in luring one of the spider's two principal prey species. If the spider could adjust its attractant blend to predictable and unpredictable variation in prey abundance, it would be a much more efficient predator and could minimize a major disadvantage of prey specialization. In this research, we propose to use a combination of chemical, electrophysiological, and behavioral approaches to determine if this bolas spider shows flexibility in its behavior or mimetic signal to improve its hunting effectiveness. Specific questions to be addressed include the following: (1) Does the spider's emitted signal change over the course of a night to correspond with the predictably different diel patterns of sexual activity of its principal prey species? (2) Does the emitted signal vary seasonally to correspond with predictable changes in abundance of its prey species? (3) Do hunting tactics and the emitted signal vary plastically with unpredictable prey availability? Studies of this system will lead to an understanding of tradeoffs involved in the evolution of exploitation of chemical communication and the role of behavioral plasticity in minimizing the costs of specialization.

This work involves a collaboration with Dr. Kenneth V. Yeargan (Entomology, University of Kentucky).

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