Genetics of Domesticated Behavior in Dogs and Foxes - Genetics and the Behavior of Domestic Animals - page 369

Multiple efforts have adopted a candidate gene approach to identify genes
associated with behavioral traits in dogs, with mostly negative results
(recently reviewed in Hall and Wynne, 2012 and Houpt, 2007 ). Positive asso-
ciations were identified for: Activity

Impulsivity with DRD4 and TH in
German Shepherds; with DAT, DBH, DRD4 in Belgian Tervuren ( Hejjas
et al., 2007, 2009; Kubinyi et al., 2012 ); activity level with SLC1A2 and
COMT in Labrador Retrievers ( Takeuchi et al., 2009a ); human-directed
aggression with DRD1, HTR1D, HTR2C, and SLC1A1 in English Cocker
Spaniels ( V˚ge et al., 2010 ); aggression with SLC1A2 in Shiba Inu
( Takeuchi et al., 2009b ), but with AR in Akita Inu ( Konno et al., 2011 ).
All these studies were performed in relatively small dog samples and none
has been validated in independent data sets. Taking into account the com-
plexity of dog behavior, the validity of this single gene approach may be
questionable.
Comparison of dog and wolf genomes identified several regions where
the two species differ most significantly ( Axelsson et al., 2013; vonHoldt
et al., 2010 ). From purely genomic data it is almost impossible to determine
whether any of these regions are causally associated with behavioral differ-
ences between dogs and wolves. One such region identified in the vonHoldt
et al. (2010) study is homologous to the region on human chromosome 7,
where a deletion causes Williams Beuren syndrome in humans, a complex
disorder associated with exceptional gregariousness ( Doyle et al., 2004;
Jarvinen-Pasley et al., 2008 ). Identification of a selection signal in the corre-
sponding canine genomic region does suggest that this region may harbor
genes influencing behavior in both species. However, as dogs diverged from
wolves so long ago and have been selected for so many different traits, one
would certainly expect their genomes to harbor multiple species-specific
selection signals not necessarily associated with behavioral differences. What
is clearly needed to complement such studies as these, is evidence of
co-segregation of genomic changes with behavior, and expression differences
of implicated genes that correlate with differences of behavior. The opportu-
nity to obtain such information is provided in studies that recapitulate canine
domestication in the silver fox.

THE FARM-FOX EXPERIMENT
The silver fox is a coat color morph of the red fox (Vulpes vulpes). In
contrast to the dog that was domesticated prehistorically, the fox was domes-
ticated in controlled farm conditions. Experimental domestication of farm-
bred foxes was started by Dmitry Belyaev and Lyudmila Trut at the Institute
of Cytology and Genetics (ICG) of the Russian Academy of Sciences, in
Novosibirsk, Russia, in the late 1950s and is still ongoing, as has been
reviewed in several publications ( Trut, 1999; 2001; Trut et al., 2004, 2009 ).
Belyaev proposed that selection for behavior was the primary force in the