Behavioral Genetics and Animal Domestication - Genetics and the Behavior of Domestic Animals - page 62

waste of energy, with food being continuously distributed and in greater
quantity. For is found to be expressed in a diverse set of tissue types, princi-
pally those involved in taste, olfaction, gut, and central brain function
(closely paralleling rat PKG1 expression ( Kroner et al., 1996 )), and thought
to be involved in the response to aversive stimuli. The association between
social behavior and neurons that respond to aversive conditions in this
instance therefore provide a mechanistic basis for these observations from
behavioral ecology. Such adverse environmental conditions often provide the
stimulus for group formation (for instance antipredation behavior in fish
( Krause and Ruxton, 2002 )).

Pigmentation and Behavior
As seen in ancient wall pictures and as is obvious from recent selection experi-
ments, loss of pigmentation seems to be one of the first and most conspicuous
phenotypic changes occurring in most domesticated species ( Clutton-Brock,
1999; Price, 2002 ). This leads to a rapid increase in frequency of spotted and
white individuals in the population. It is of course quite possible that the
fast emergence of hypo-pigmented individuals is a result of directed human
selection of rare, spontaneous mutations. For example, white and spotted indi-
viduals may have been easier to find and recognize, and to distinguish from
the wild ancestors, which would have been abundant around the early farm
villages, and hence may have been perceived as more attractive. However,
it is also possible that loss of pigmentation is related to tameness and reduced
stress sensitivity, as we discussed earlier in the perspective of the Belyaev
experiment on foxes. In this case, non-pigmented animals may have developed
spontaneously and could have been favored during selection either because of
their visual attractiveness or because of their tameness, or both.
Several studies of different species indicate a clear correlation between
pigmentation on the one hand and stress sensitivity or fearfulness on the
other. For example, non-pigmented mink are generally easier to handle than
their colored conspecifics ( Trapezov et al., 2008 ) and in wild vertebrates,
darker and more pigmented species and populations are generally more
aggressive and more sexually active ( Ducrest et al., 2008 ). Salmon selected
for low cortisol response in a stress test have fewer pigmented skin spots
than more stress-prone individuals ( Kittilsen et al., 2009 ).
Skin and hair pigment come in two different variants: black eumelanin,
and red phaeomelanin. The phenotypic expression of both is mediated by the
melanocortin receptor, which, in turn, exists in five different variants, present
in different tissues. The most important one for the expression of pigmentation
is melanocortin receptor 1 (MC1R), a G-protein-coupled receptor in melano-
cytes. When bound to the agonist -MSH (melanin stimulating hormone)

the receptor causes a cascade of reactions leading to the deposition of black

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