Chemical alarm signals in wild Trinidadian guppies (Poecilia reticulata)

We investigated the presence and possible function of chemical alarm signals (alarm pheromones) in wild Trinidadian guppies (Poecilia reticulata) using laboratory, trapping, and direct field observational methods. In laboratory experiments, female guppies from a population exposed to high predation significantly increased their shoaling, dashing, and freezing behaviours and significantly reduced area use when exposed to the skin extract of sympatric female guppies. When exposed to the skin extract of females from a low-predation population, female guppies from a high-predation population exhibited significant, though smaller, increases in antipredator behaviour. No significant differences in antipredator behaviours were noted when females were exposed to swordtail (Xiphophorus helleri) skin extract, which lacks any known alarm pheromone. We conducted two field experiments to confirm these laboratory results. In a trapping experiment, significantly more guppies were caught in funnel traps labelled with distilled water than in paired traps labelled with sympatric guppy skin extract. In a final experiment, a realistic model of a natural predator (pike cichlid, Crenicichla alta), paired with either sympatric guppy skin extract or distilled water, was presented to groups of free-ranging guppies in pools of a high-predation river. Significantly fewer guppies were observed within a 50-cm radius of the predator model and significantly fewer guppies inspected the model when it was paired with guppy skin extract versus distilled water. Taken together, our results strongly suggest the presence of a chemical alarm signal (alarm pheromone) in the Trinidadian guppy, establish the validity of laboratory and trapping studies in the investigation of chemical alarm signalling, and demonstrate that alarm pheromones may function to mediate predation risk under natural conditions in the guppy.

Anti-Predator Responses To Conspecific and Heterospecific Skin Extracts By Threespine Sticklebacks: Alarm Pheromones Revisited

Under laboratory conditions, we investigated the presence of chemical alarm signals in the threespine stickleback (Gasterosteus aculeatus). We exposed individual threespine sticklebacks to skin extract of conspecifics originating from either the same or a different population, fourspine sticklebacks (Apeltes quadracus; a member of the same prey guild as the threespine stickleback) or swordtails (Xiphophorus helleri), a species not known to possess alarm pheromones and which is phylogenetically distant and allopatric from the threespine stickleback. Threespine sticklebacks exhibited significant increases in anti-predator behaviour patterns when presented with skin extract from both populations of conspecifics and from fourspine sticklebacks, but not to swordtail skin extract. These results suggest, contrary to previous reports, that threespine sticklebacks possess chemical alarm signals, which appear to be similar to those of Ostariophysan fishes.