Coral degradation impairs learning of non-predators by Whitetail damselfish

A prerequisite for effective antipredator responses is the ability of the
prey to distinguish animals that pose a threat from those that do not.
Prey often have efficient learning mechanisms to learn threats but
learning to recognize nonpredators may be equally or more important.
Moreover, the ability to generalize learned information is of key
importance for prey animals. Prey take information they know about one
species to make ‘educated guesses’ about the predatory/nonpredatory status
of other unknown species. Here, we investigate the ability of Whitetail
damselfish (Pomacentrus chrysurus) to learn the identity of non-predators
and then generalize their responses to other unknown animals. Our work is
completed within the context of unprecedented habitat degradation in reef
ecosystems. When corals die, the remaining skeleton is colonized by algae,
cyanobacteria and sessile invertebrates. These opportunistic colonists
change the physical and chemical landscape of the reef and hence the
background odour in which predator and non-predator recognition occurs.
Our results indicated that Whitetail damselfish (Pomacentrus chrysurus)
learn to classify Moonwrasse (Thalasomma lunare) as a non-predator through
the process of latent inhibition, whereby the prey are repeatedly exposed
to Moonwrasse odour multiple times in the absence of negative
reinforcement. These fish subsequently generalized their nonpredator
recognition to other unknown wrasse, but not distantly related fish. Of
key importance was our finding that the patterns and extent of
non-predator learning and generalization were dramatically altered in dead
coral habitats. As predicted, prey that learned the Moonwrasse as a
nonpredator in live coral environments did not subsequently respond to
Moonwrasse when we tried to teach them Moonwrasse was a predator in live
coral. However, this non-predator recognition was reduced in dead coral
environments. Moreover, generalization completely failed when we changed
from live to dead coral environments. Juvenile damselfishes need to
rapidly catalogue the identity of unknown animals when they arrive at a
reef. Changing background odours, that occur with changing tides and
currents, means that prey need to learn non-predator identities separately
in each water source. This cognitive challenge likely has significant
survival consequence in a changing environment.