Abstract
According to current evolutionary theory, insect pheromones can originate from extant precursor compounds being selected for information transfer. This is exemplified by females of the parasitoid wasp Leptopilina heterotoma whose defensive secretion consisting mainly of (−)-iridomyrmecin has evolved secondary functions as cue to avoid other females during host search and as female sex pheromone. To promote our understanding of pheromone evolution from defensive secretions we studied the chemical ecology of Leptopilina clavipes. We show here that L. clavipes also produces a defensive secretion that contains (−)-iridomyrmecin as major component and that females use it to detect and avoid host patches occupied by other females. However, the female sex pheromone of L. clavipes consists solely of cuticular hydrocarbons (CHCs) and males did not respond to female CHCs if presented in combination with the defensive secretion containing (−)-iridomyrmecin. This is in contrast to other species of Leptopilina, in which the iridoid compounds have no inhibiting effect or even function as sex pheromone triggering courtship behaviour. This indicates that Leptopilina species differ in the cost-benefit ratio for males searching for females, which might explain the strong divergence in the composition of the sex pheromone in the genus.
Highlights
Information transfer via chemical compounds is the most ancient and widespread form of communication and is found in bacteria, fungi, plants, and the animal kingdom
Only in L. boulardi have the iridoid compounds from the defensive secretion become a part of the sex pheromone, while the sex pheromone of L. victoriae consists of only cuticular hydrocarbons (CHCs)
To better understand the evolution of sex pheromones from defensive secretions we studied the chemical ecology of the congeneric species L. clavipes by analysing the composition of its defensive secretion and by testing the role of the defensive compounds in the females’ host patch choice and sex pheromone
Summary
Information transfer via chemical compounds is the most ancient and widespread form of communication and is found in bacteria, fungi, plants, and the animal kingdom. Any compound that is released by one individual and detected by another individual of the same species can acquire a communicative function and evolve into a chemical signal In this way, for example, a hormone excreted with urine, a compound present on the cuticle of an insect to prevent desiccation, or a constituent of a defensive secretion released upon a predatory attack may serve as the starting point for the evolution of a pheromone. If this response benefits both the releasing and the receiving individual, chemical ritualization of information transfer via this compound may result in it becoming a true chemical signal[1,2,3] Prime examples of this evolutionary process are the female sex pheromones of the goldfish and the Atlantic Salmon which have evolved from steroid and prostaglandin hormones contained in the urine of females[5]. Only in L. boulardi have the iridoid compounds from the defensive secretion become a part of the sex pheromone, while the sex pheromone of L. victoriae consists of only CHCs
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