In the recent paper “Learning to Avoid Dangerous Habitat Types by Aquatic Salamanders, Eurycea tynerensis” Alicia Mathis and Shem Unger, present evidence of habitat selection based on learning. Aquatic salamanders can be paedomorphic throughout the course of their life and confined to the water. As a result, they often live alongside their predators and the selection pressure to avoid these predators is expected to be high. The species of focus in this study, the Oklahoma salamander shares the benthic streams with the syntopic predatory fish, the banded sculpin.
The banded sculpin is visually cryptic, so the likely means for evaluating predatory risk assessment for the salamander is to use chemical cues. Experiments were set up to present three different chemical cues: the predator (sculpin), nonpredator (tadpole) or blank control (water). There three possible cues were presented with either rocks or grass in the tank for training sessions. The same salamanders were tested 2 days later in a tank divided into thirds. The test individual was placed in the center neutral region and given basically a choice test of rocks on one side and grass on the other. There were no cues present in the testing phase and it was only to measure the time spent in the rock or grass habitat in consideration of the learning trial cue pairing. The expectation being that if the salamander has learned to associate the predatory cue with a specific habitat the individual will spend less time in that area.
Indeed, the results indicate that the Oklahoma salamanders were able to learn to avoid the habitats where they had experienced the predatory chemical cues. There was no significant effect of habitat found which is to say the salamanders are able to avoid both grass and rocks.
Certainly this is a straightforward study of learning, however these salamanders were taken from streams where they already encounter the sculpin. It would be interesting to see how the same species not previously exposed to the sculpin would fare in the trials. Also, the authors cited other work suggesting that the Oklahoma salamander was actually a rarity in the diet of the banded sculpin (Tumlison and Cline 2002), which brings up the issue of using chemical cues from the primary predator in this food web instead of a fish that rarely eats the salamander.
Photo Credit: Michael Steffen