Just Keep Learning, Just Keep Learning…

Last week we discussed how horses are able to learn from other horses to access hidden food. This week, I’d like to talk about whether very different animals can also utilize social learning: sharks and fish.

320px-Lemon_shark2I’ve never thought of sharks as social animals, so it surprised me that someone would investigate whether sharks can socially learn. However, while many shark species are solitary, some species do live in groups. Guttridge et al. (2013) studied the ability of one such species, the lemon shark, to learn from other lemon sharks.

They taught one group of lemon sharks (the “demonstrators”) to approach an underwater target, then rewarded them with food. Once the sharks had learned this association, one demonstrator was paired with a naïve “observer” shark and completed five trials. Then the demonstrator was removed and the observer was tested alone.

Guttridge et al. also had a control group of “sham” demonstrators, which had not been trained on the task. These sharks were also paired with naïve observers, exposed to five trials of the task, and removed. Then the “sham” observers were tested. The performance of the observers was compared to that of the sham observers to rule out the possibility that the observers’ behavior was due to merely being in the presence of another shark.

The researchers found that the observers completed more trials than the sham observers. Additionally, the observers were much faster to complete their very first trial than the sham observers, although the sham observers quickly learned the task from experiencing it themselves. Even though the sham observers caught up to the observers in performance, the fact that the observers were quicker on the first trial indicates that social learning did occur.

At its most basic level, social learning means learning about one’s environment from a more experienced individual. We’ve seen how social learning can be used for the purpose of obtaining food in an animal’s environment. Can social learning be used to avoid dangers in an environment as well?

320px-Acanthochromis_polyacanthus

Tropical Damselfish (A. polyacanthus)

Manassa & McCormick (2012) investigated this question in tropical damselfish. The researchers wanted to see if damselfish could learn to recognize a predator solely based the behavior of another damselfish. Recognition of a predator was indicated by an “anti-predator response”: remaining close to shelter (in this case, a rock in the tank).

First the researchers made sure that the damselfish didn’t initially recognize a particular predator fish’s odor by pouring 60 mL of water from the predator fish’s tank into the damselfish tanks, and observing the damselfishes’ responses. The damselfish showed no anti-predator response, confirming that they didn’t instinctively recognize the predator fish.

Next the researchers conditioned a group of damselfish to recognize the predator. To do this, they utilized an interesting trait of damselfish (and some other fish species): the fish release a chemical alarm signal when injured, which warns nearby conspecifics (members of the same species) of a possible threat. Manassa & McCormick added predator odor to the tanks of “demonstrator” damselfish, followed by damselfish chemical alarm signal. They later tested these damselfish by adding just predator odor to their tanks. The demonstrators exhibited an anti-predator response, remaining close to shelter, proving that they now recognized the predator fish.

ChocHind

Predator Fish: Chocolate Hind (C. boenak)

In the next stage, demonstrators were paired with naïve damselfish and predator odor was once again added to the tank. Finally, the demonstrator was removed, predator odor was added a final time, and the behavior of the previously naïve (now “conditioned”) damselfish was observed.

Manassa & McCormick found that, compared to control damselfish that had been paired with other naïve damselfish, the conditioned damselfish moved closer to shelter in response to the predator odor. In fact, their response was no different from the response of the demonstrator damselfish that had been trained with both predator odor and the chemical alarm signal. These results indicate that tropical damselfish can socially learn about predators.

So it turns out that animals across the animal kingdom can utilize social learning to learn about their environments and increase their chances of survival. Next week we’ll finish up talking about social learning with an example of social learning interacting with genes!

Here’s a cool video detailing a few other social learning experiments in fish. (The title, “Culture in Fish”, may seem a bit surprising, as we don’t usually think of animals as having culture. It’s still a controversial idea in the fields of animal behavior and cognition, and I’m hoping to go into more detail in a future post. But suffice it to say that many scientists contend that social learning is closely tied to culture.)

Sources Cited:

Guttridge, Tristan L., et al. “Social learning in juvenile lemon sharks, Negaprion brevirostris.” Animal cognition 16.1 (2013): 55-64.

Manassa, R. P., and M. I. McCormick. “Social learning and acquired recognition of a predator by a marine fish.” Animal cognition 15.4 (2012): 559-565.

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