Behavioral Genetics and Animal Domestication - Genetics and the Behavior of Domestic Animals - page 66

locus close to AVPR1a caused the birds to show breed typical differences
in males, but not females, indicating that the gene may be a major player in
causing the domestication induced differences in social behavior. As a
further support to this, the gene is differentially expressed in the part of the
brain containing the ventral pallium when comparing Red Junglefowl and
White Leghorn males ( Wir´n, 2011 ).
Of course, these studies are purely based on correlations, and the effects
could just as well be caused by any other linked gene in the same region.
However, it is intriguing that several socially potent neuropeptide genes are
located in the same small genomic region. It remains to be studied which
mutations may underlie the different expression rates and it is also as yet
uncertain to what degree this locus is involved in shaping social behavior in
chickens. Furthermore, neither of the neuropeptides or their receptors has
been studied with respect to domestication in mammals, so the story remains
a thought-provoking idea at this time.
Different Means to the Same Ends
The traditional domesticated animals have a history of thousands of years
of living with humans, making it very difficult to pinpoint early genetic
responses to the altered selection. However, studies of recently added mem-
bers to the domesticated fauna may be interesting in this respect. Many fish
species have been domesticated only in the last hundred or so years, while at
the same time being under similar selection pressures as other domesticates.
For example, they are bred to grow faster than their ancestors in an environ-
ment where food is abundant and predation is virtually absent.
Tymchuk and colleagues studied gene expression profiles in domesticated
rainbow trout and their wild conspecifics in different tissues, and further
compared this to other domesticated salmonids ( Tymchuk et al., 2009 ). They
found that transcription profiles could differ substantially between different
species, but taken together they target the same physiological end-point.
The common denominator appears to be to affect the Growth Hormone gene,
and the closely associated IGF1. This suggests that although the phenotypic
target is the same, the genetic networks are sufficiently complex and flexible
to cause a similar phenotypic effect by means of different pathways. This
would be an important argument against the previously mentioned hypothesis
that domestication is a single-gene event.
The fish studies also demonstrate the existence of important pleiotropic
effects, which conversely adds some support to the idea that broad pheno-
typic alterations can be caused by selection of a single trait. For example,
Johnsson et al. (1996) studied brown trout (Salmo trutta) which were either
hatchery raised or injected with growth hormone. Both treatments caused a
similar increase in growth rate. Irrespective of whether growth had been
increased by selective breeding or by hormonal manipulations, the correlated