Learning

Overview

Photo Credit: Matthew D Potenski

 

Many animals live in complex environments that are constantly changing. In response to such environments many organisms have evolved different levels of phenotypic plasticity that allow for short- and long-term adaptive changes in morphology and behaviour. One such adaption is learning, which is most commonly defined as a change in behaviour as a result of experience. Learning plays a significant role in the behavioural flexibility of fish in a wide range of contexts, including orientation, anti-predator behaviour and foraging. Recent evidence has suggested that some of the learning abilities of teleost fishes are comparable to land vertebrates and that the processes used are strikingly similar. Dr. Gruber pioneered some of the first shark learning studies here we highlight these and describe some more recent findings where sharks learn from each other!

  1. How do sharks compare to other animals in their ability to learn a classical conditioning regime?
  2. Are lemon sharks able to learn from each other?

Studies investigating learning behavior in sharks provide important information about shark ecology and have implications for fisheries and ecotourism practices. They also all us to investigate how learning processes evolved across the vertebrate lineage. In the public domain, sharks have a poor reputation they are often referred to as ‘mindless killers’ or ‘swimming noses’ and attacks on humans, albeit rare, gain huge exposure. However, despite this negative press and hysteria surrounding sharks there still remains a real interest and fascination with them, thus studies investigating learning may also help to change public perception.

  1. Classical conditioning of the nictitating membrane response in juvenile lemon sharks
Classical conditioning occurs when two events overlap in time and space so that an originally neutral stimulus can be associated with an aversive or rewarding stimulus. This study was the first authoritative account of classical conditioning in sharks. Training involved restraining the shark while exposing it to a conditioning stimulus (CS, light flash) that was paired with an unconditioned stimulus (US, electric shock), producing an eye-blink response. Dr. Gruber tested 20 juvenile lemon sharks each exposed to 100 trials per day for seven consecutive days finding that:
  • Classical conditioning of the nictitating membrane response occurred reliably in lemon sharks.
  • Lemon sharks had comparable learning characteristics to mammals, with lemon sharks exhibiting gradual recovery when exposed to extinction sessions (where the electric shock is removed and conditioned response becomes independent of the CS).

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Juvenile lemon shark with nictitating membrane partially closed.
  1. Social learning in juvenile lemon sharks
Here we designed a novel food task, where sharks were required to enter a start zone and subsequently make physical contact with a target in order to receive a food reward (can have setup from paper and or video). Naive sharks were then able to interact with and observe (a) pre-trained sharks ‘demonstrators’, or (b) sharks with no previous experience ‘sham demonstrators’. On completion, observer sharks were then isolated and tested individually in a similar task. We tested 5 groups of 4 sharks over a period of 4 months finding that:
  • During the exposure phase observers paired with ‘demonstrator’ sharks performed a greater number of task-related behaviours than observers paired with ‘sham demonstrators’.
  • When tested in isolation, observers previously paired with ‘demonstrator’ sharks completed a greater number of trials and made contact with the target significantly more often than observers previously paired with ‘sham demonstrators’. Such experience also tended to result in faster overall task performance.
Depiction of the target in both closed and open positions.
 
These results indicate that juvenile lemon sharks, like numerous other animals, are capable of using socially derived information to learn about novel features in their environment and likely have important implications for behavioural processes, ecotourism and fisheries.
 
Principal Investigator
Dr. Tristan Guttridge - Cardiff University, UK
Mr. Sander Van Dijk - University of Groningen, Netherlands
 
Collaborators
Prof. Jens Krause - Humboldt University, Germany
Dr. Culum Brown - Macquarie University, Australia
Dr. Samuel H. Gruber - University of Miami, US
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