Conditional signalling strategies: effects of ontogeny, social experience and social status on the pheromonal signal of male cockroaches

Abstract

Social interactions amongNauphoeta cinerea(Dictyoptera: Blaberidae) are mediated primarily through pheromonal signals. Males produce a three-component pheromone blend that attracts females and influences the close-range interactions between the sexes. Ontogenetic changes were documented in the quantity of pheromone produced by socially isolated males that ranged in age from adult emergence to 50 days after emergence. Pheromone quantity paralleled the development of male attractiveness to females, male sexual competence and male agonistic behaviour. Although males are sexually mature at 6 days of age, the quantity of 2-methylthiazolidine and 4-ethyl-2-methoxyphenol in their glands continued to increase beyond that age, while the quantity of 3-hydroxy-2-butanone reached a plateau by 4 days of age. The quantity of the former two components returned to a baseline level after long-term isolation. In addition to ontogenetic changes, social experience altered the quantity of pheromone produced. Both winning in male-male agonistic encounters and mating apparently stimulate the production and/or release of male pheromone. The quantities of 2-methylthiazolidine and 4-ethyl-2-methoxyphenol were reduced in the glands of dominant males but not subordinate males. Although the quantities changed, the ratio of 2-methylthiazolidine to 4-ethyl-2-methoxyphenol was not different between dominant and subordinate males. All males showed reduced quantities of 2-methylthiazolidine and 4-ethyl-2-methoxyphenol 48 h after mating but showed no change in 3-hydroxy-2-butanone or the ratio of 2-methylthiazolidine to 4-ethyl-2-methoxyphenol. Potential functional integration for two of the three pheromonal components is suggested by the similar pattern of synthesis and depletion of 2-methylthiazolidine and 4-ethyl-2-methoxyphenol. The unique pattern of synthesis and lack of depletion of 3-hydroxy-2-butanone suggests there may be an independent role for this compound. The differential depletion of these components suggests that the active release of the pheromone byN. cinereamales may be a conditional strategy, with the specific tactic depending on previous social experiences.