Behavioral Genetics and Animal Domestication - Genetics and the Behavior of Domestic Animals - page 69

exposed rats to the environmental pollutant vinclozolin, which caused a
dramatic effect on the methylation states and expression levels of many
genes, and also affected their stress responses and anxiety-related behavior
( Skinner et al., 2008 ). Both the epigenetic effects and the behavioral modifi-
cations were clearly measureable in the third, untreated offspring generation.
This shows that epigenetic effects may alter phenotypes in ways similar to
those of DNA-mutations (although perhaps often in a reversible manner),
and offers a hypothetical novel route for rapid evolutionary changes in
response to, for example, environmental stress. A broad review of studies
supporting this has been provided by ( Jablonka, 2009 ).
Since domestication is an example of precisely such a rapid evolutionary
process, causing wide phenotypic modifications in a short time, it is quite likely
that epigenetic mechanisms may play an important role here. Lindqvist and
coworkers studied this in chickens, by exposing groups of ancestral Red
Junglefowl and domesticated White Leghorns to chronic stress during rearing
(using an unpredictable light scheme as the stressor), and measured the outcome
on a spatial learning task. In both breeds, stressed birds showed a reduced
learning ability compared to control groups ( Lindqvist et al., 2007 ). However,
only in domesticated chickens was this decreased learning mirrored in the
offspring. Using microarray analysis, the authors found that stress-induced
brain gene expression differences were correlated across generations in domesti-
cates, but again, not in Red Junglefowl. Hypothetically, it was suggested that
domestication could have selected animals with an increased capacity to
respond epigenetically to environmental stress, and to transfer these responses
to the next generation. In effect, the suggestion is that domestication may have
selected animals with a higher evolvability ( Carter et al., 2005 ), which would
have speeded up the pace of evolution considerably.
This suggestion is as yet hypothetical and speculative, but it has received
a certain experimental support lately. N¨tt and colleagues used microarrays
to analyze differential gene expression in the hypothalamus regions of a
small number of families of Red Junglefowl and White Leghorn, and in
addition studied the methylation differences in the promoter regions of more
than 3000 of the same genes ( Natt et al., 2012 ). The families were selected
based on divergent results in a fear test, so within each breed there were
highly fearful and less fearful individuals. As in the previous studies by
Lindqvist et al. (2007 ), fearfulness was significantly correlated between gen-
erations in White Leghorns, but not in Red Junglefowl, again indicating that
the ability for

transgenerational effects may have been favored during

domestication.
Comparing the breeds, close to 300 genes were differentially expressed
in the parents, and more than 1600 in the offspring. Gene Ontology (GO)
analysis showed that genes belonging to pathways associated with stress
responses, memory consolidations, neural differentiation and reproduction
were enriched among the differentially expressed ones. Looking at promoter