Domesticated chickens have smaller brains

Date:
August 26, 2020
Source:
Linko"ping University
Summary:
Researchers suggest a process by which the timid junglefowl from the
rain forest could have become today's domesticated chicken. When the
scientists selectively bred the junglefowl with least fear of humans
for 10 generations, the offspring acquired smaller brains and found
it easier to become accustomed to frightening but non-hazardous
events. The results shed new light over how domestication may have
changed animals so much in a relatively short time.



FULL STORY ========================================================================== Researchers from Linko"ping University suggest a process by which
the timid junglefowl from the rain forest could have become today's domesticated chicken.

When the scientists selectively bred the junglefowl with least fear of
humans for 10 generations, the offspring acquired smaller brains and
found it easier to become accustomed to frightening but non-hazardous
events. The results shed new light over how domestication may have
changed animals so much in a relatively short time.


========================================================================== Chickens are the most common birds on Earth. There are currently more than
20 billion individuals on the planet. All of them have come from the Red Junglefowl, originally found in south-east Asia. This species was tamed
and domesticated by humans approximately 10,000 years ago. The results
of the current study show that when our ancestors selected the tamest individuals for breeding, they may at the same time have unconsciously
selected birds with a different brain -- one that may have been more
suitable for a life among humans. The findings are published in Royal
Society Open Science.

Researchers Rebecca Katajamaa and Per Jensen started with a group of wild
Red Junglefowl and selected as parents the birds that showed least fear
of humans in a standard test. The breeding experiment was conducted for
10 generations.

The birds that showed greatest fear of humans were placed into a second
group.

The researchers believe that they have in this way imitated the factor
that must have been the most important during early domestication,
namely that it was possible to tame the animals.

A somewhat unexpected result of the breeding was that the brains of
the domesticated birds gradually became smaller relative to body size,
which mirrors what has happened to modern domesticated chickens during
the domestication process. The change was particularly pronounced in the
brain stem, a primitive part of the brain that is involved in, among
other things, certain stress reactions. The brain stem was relatively
smaller in animals that were not overly timid.

The scientists carried out two behavioural experiments, to determine
whether the difference in brain size and composition affected the ability
of the fowl to learn. One test investigated how rapidly the birds became accustomed to something that could be experienced as frightening, but
which was actually non- hazardous, in this case a flashing light. The tame birds became accustomed and stopped reacting to the stimulus significantly
more rapidly.

"We believe that the ability to become accustomed rapidly is beneficial
for the birds that are to live among humans, where events that are
unknown and frightening, but not dangerous, are part of everyday life,"
says Rebecca Katajamaa, doctoral student in the Department of Physics, Chemistry and Biology at Linko"ping University.

The researchers also investigated whether the birds differed in the
ability to learn to associate two things with each other, such as coupling
a certain pattern with food. This process is known as "associative
learning." However, they found no differences between the two groups.

It is not possible to say whether the differences in behaviour shown in
the study are directly connected with the differences in brain size and composition. The researchers plan to investigate this in more detail.

"Our study not only sheds light on a possible process by which chickens
-- and possibly other species -- become domesticated. It may also give
new insight into how the structure of the brain is connected with
differences in behaviour between individuals and species," says Per
Jensen, professor in the Department of Physics, Chemistry and Biology
at Linko"ping University.

The research has received financial support from the Swedish Research
Council.


========================================================================== Story Source: Materials provided by Linko"ping_University. Original
written by Karin So"derlund Leifler. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Rebecca Katajamaa, Per Jensen. Selection for reduced fear in red
junglefowl changes brain composition and affects fear memory. Royal
Society Open Science, 2020; 7 (8): 200628 DOI: 10.1098/rsos.200628 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200826101619.htm

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