Volatile nematode sex pheromones

Abstract

Nematodes produce a staggering array of sol. social cues, glycosides of dideoxy-sugars such as the ascarylose (ascarosides), that are secondary metabolites and communicate information such as population d. and location of sex partners. We found that predatory fungi respond to certain ascarosides by making sticky traps that trap and kill nematodes. This finding suggested that one driver of the evolution of ascaroside prodn. is avoiding predation. We have recently identified using GC-MS of the head-space of cultures of two distant genera of nematodes - the fungal-feeding and tree-parasitic Bursaphelenchus and the fruit-assocd., free-living Caenorhabditis - a set of volatile compds. that are produced by nematodes and attract sex partners. These compds. are hexenyl acetates and relatives. The prodn. of, and response to, these volatiles are genus specific, suggesting that the volatile pheromones might be under similar selective pressures as the sol. pheromones. Indeed, the same predatory fungi that senses ascarosides as a proxy for nematodes attract nematodes by prodn. of volatile org. compds. One of these, methyl-2 methyl-3 butenoate, is a potent attractor of hermaphrodite (female) nematodes but not males, suggesting that it mimics endogenous volatile pheromones. The prodn. of volatile pheromones by females is regulated by their sperm status: only unmated females produce the pheromone, suggesting a way to identify candidate genes that control pheromone prodn.