Chemical Communication in the German Cockroach: Pheromones and Heterospecific Courtship Eliciting Compounds

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Title: Chemical Communication in the German Cockroach: Pheromones and Heterospecific Courtship Eliciting Compounds
Author: Eliyahu, Dorit
Advisors: Coby Schal, Committee Chair
Edward L. Vargo, Committee Member
Robert R. H. Anholt, Committee Member
Charles S. Apperson, Committee Member
Abstract: Sexual communication is vital for the reproductive success of many species. Chemical communication is considered highly effective in being both species-specific and indicative of reproductive status. However, there are cases in which this intraspecific intersexual system breaks down, either by sexual mimicry or by convergence on similar compounds in different species. In the first chapter I review the literature for cases where courtship displays are chemically elicited by non-reproductive conspecifics and by heterospecifics. I group cases as being (1) adaptive to courting males; (2) maladaptive to courting males; or (3) incidental consequences of convergence on similar courtship releasing cues of no adaptive value to either participant in courtship. Volatile sex pheromones, responsible for bringing of the sexes together, have been studied extensively. On the other hand, contact sex pheromones which are vital for reproductive success in many species, have received much less attention and little is known about their chemistry and biochemical and hormonal regulation. An exception is the German cockroach, Blattella germanica, whose contact sex pheromone has been extensively studied in relation to endocrine regulation of pheromone biosynthesis. Here I report on investigations of chemical structure-activity relationship in the German cockroach using naturally occurring and synthetic courtship eliciting compounds. I show that contrary to expectation, the naturally occurring stereoisomer of the pheromone, (3S,11S)-dimethylnonacosan-2-one, is the least active of the four possible stereoisomers. Extensive behavioral assays with synthetic pheromone analogs and the natural pheromone were conducted to validate this result. Next I identify two additional contact sex pheromone components, predicted from the proposed biosynthetic pathway, and confirm their behavioral activity with synthetic compounds. I used a behavioral-assay guided approach whereby fractions from flash column chromatography, high performance liquid chromatography and gas chromatography were behaviorally assayed and the active components identified with mass spectrometry. In addition, I describe two intriguing phenomena where courtship is directed toward non-receptive individuals: the German cockroach male courts immatures of its own species, as well as members of five other cockroach species. I used a similar behavior-guided chemical fractionation approach to purify and identify from nymphs compounds responsible for eliciting courtship. The results show that last instar female nymphs share common pheromonal components with the adult female contact sex pheromone. I also isolated a different, yet to be identified compound, or set of compounds, from young nymphs and last instar female nymphs that elicit courtship in Blattella males. The nymphs may elicit courtship as a potentially adaptive strategy of sexual mimicry, whereby they avoid aggression from males or gain nutritional benefits from the courting male. Five other cockroach species can elicit courtship in German cockroach males, and the courtship eliciting compounds in Blatta orientalis were identified as related to, but different from any of the sex pheromone components of B. germanica. This suggests that the German cockroach male responds to a broader range of chemical structures than necessary for sexual and species recognition. Possible conditions favoring this broad sensory tuning are discussed.
Date: 2007-08-07
Degree: PhD
Discipline: Entomology

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