Selection for reduced fear in red junglefowl changes brain composition and affects fear memory

Area of Science:

• Animal Behavior
• Neuroscience
• Evolutionary Biology

Background:

• Brain size reduction is a common characteristic observed in domesticated species compared to their wild counterparts.
• Cerebral changes in domesticated animals are often linked to behavioral selection during the domestication process.

Purpose of the Study:

• To investigate the effects of artificial selection for diverging fear levels on brain size and composition in red junglefowl.
• To assess the impact of fear-related selection on learning abilities, specifically habituation and conditioned place preference.

Main Methods:

• Red junglefowl were selectively bred for 10 generations based on their fear response to humans.
• Brain size, brain composition, and learning behaviors (habituation, conditioned place preference) were measured in the selected lines.
• Statistical analyses accounted for allometric effects to evaluate brain size differences relative to body size.

Main Results:

• Chicks from the low-fear line exhibited significantly smaller brain sizes relative to body size and smaller brainstem regions compared to the high-fear line.
• After accounting for allometric effects, the significant brain size differences diminished, but a trend towards larger cerebra in low-fear chickens persisted.
• Low-fear chicks demonstrated more effective habituation to a fearful stimulus, while high-fear chicks showed no significant change in response after prior experience.

Conclusions:

• Artificial selection for reduced fear in red junglefowl influences brain size and composition, particularly affecting the brainstem and potentially the cerebrum.
• The observed changes in brain structure and habituation learning in low-fear chickens align with typical effects of domestication.
• This study provides insights into the neurobiological underpinnings of behavioral changes associated with domestication and artificial selection.