Brain development and predation: plastic responses depend on evolutionary history

Although the brain is known to be a very
plastic organ, the effects of common ecological
interactions like predation or competition on
brain development have remained largely
unexplored. We reared nine-spined sticklebacks
(Pungitius pungitius) from two coastal marine
(predation-adapted) and two isolated pond
(competition-adapted) populations in a factorial
experiment, manipulating perceived predatory
risk and food supply to see (i) if the treatments
affected brain development and (ii) if there was
population differentiation in the response to
treatments. We detected differences in plasticity
of the bulbus olfactorius (chemosensory centre)
between habitats: marine fish were not plastic,
whereas pond fish had larger bulbi olfactorii in
the presence of perceived predation. Marine fish
had larger bulbus olfactorius overall. Irrespective
of population origin, the hypothalamus was
smaller in the presence of perceived predatory
risk. Our results demonstrate that perceived
predation risk can influence brain development,
and that the effect of an environmental factor
on brain development may depend on the evolutionary
history of a given population in respect
to this environmental factor.