In the realm of predation there are specialists and generalists. If you are a prey item, a specialist will mostly target you and your kind, whereas a generalist is not as picky. Now, if you are an aquatic salamander hanging out in the murky water, just going about your business and sensing chemical cues, you don’t want either type of predator to eat you. In the case of the greater siren (Siren lacertina) you would flush your gills as a detection response to detect the chemical cues in the water and do a “reversal”: pulling your head and body back into an S-shape as an avoidance response. But, oohhh snap! you’re an ectotherm and this reversal stuff is energetically costly business! According to the Predator Continuum Hypothesis (Ferrari et al., 2007) you should save your strongest response (reversals) for the greatest threat (specialized predator).
In the recent paper from Ethology, B.A. Crawford et al., (2012) this idea is tested with the greater siren. The authors provide evidence with a lovely set of experiments using kairomone presentation and siren response (gill flushing, reversals). The kairomones, or chemical cues in the water are used by sirenids in the murky water as their primary cue to find food and avoid predators. In this case, the specialist predator is the mudsnake (Farancia abacura) and the generalist is the banded watersnake (Nerodia fasciata). Chemical cues from these predator snakes were obtained from the water in their surrounding tanks. As controls, the authors used blank and chemical cues from a hogsnake which in this case is a novel predator control because they are not predators of greater sirens. The sirens were placed into aquaria, allowed to acclimate and the stimuli (chemical cues) were introduced while responses were recorded.
The results from these straightforward experiments indicated that chemical cues from the specialist predator resulted in increased gill-flushing as well as reversal behavior when compared to the generalist predator. Interestingly, the authors also found that sirens had an increased gill-flushing, but not reversals in response to the novel hognose stimulus in comparison to the blank control. This suggests perhaps increased vigilance to novelty, but abstaining from the energetically costly reversal.
These experiments would be an interesting way to examine the effects of prior experience or exposure to a predator. Also, the authors bring up the point in the discussion of the possibility of prey recognizing closely related predator species and this would be similarly simple to test in their set up.
Crawford, B.A., Hickman, C.R., and Luhring, T.M. 2012: Testing the threat-sensitive hypothesis with predator familiarity and dietary specificity. Ethology 118: 41-48.
Ferrari, M.C.O., Gonzalo, A., Messier, F. and Chivers, D.P. 2007: Generalization of learned predator recognition: an experimental test and framework for future studies. Proc R. Soc. Long. Ser. B-Bio Sci 274, 1853-1859.