Genetics of Domesticated Behavior in Dogs and Foxes - Genetics and the Behavior of Domestic Animals - page 374

( Oskina and Tinnikov, 1992; Popova et al., 1997 ). Significant differences in
hypothalamic

adrenocortical (HPA) system reactivity in ontogen-
esis were observed between foxes from tame and unselected populations
( Oskina, 1996; Trut and Oskina, 1985 ). Significantly lower density of seroto-
nin 5-HT 1A receptors was observed in the hypothalamus; and significantly
higher levels of serotonin and tryptophan hydroxylase were detected in the
midbrain and hypothalamus of domesticated strain of foxes ( Popova et al.,
1997 , 2007; Trut, 2001 ). The transformation of the seasonal reproductive pat-
tern was also observed. Some foxes from the tame population showed sexual
activity outside of the regular breeding season and a few females have been
mated twice in a year, a pattern which was not recorded for foxes in nature
or in commercial bred populations ( Belyaev and Trut, 1983; Trut 1980b ).
Several de novo traits were detected in the fox population selected for
tameness. In particular, coat color changes such as the appearance of a white
spot on the head (Star phenotype) and loss of pigment in other areas began
to appear in the eighth selected generation ( Belyaev et al., 1981 ). It is
intriguing that white spotting, which appeared without direct selection or
inbreeding in the tame fox population, is frequently observed as a distinctive
difference between domesticated animals of several species (dogs, cats,
cattle, horses, etc.) and their wild progenitors. Other morphological charac-
teristics also arose in the same manner: some foxes had floppy ears until sig-
nificantly older age than foxes from commercial populations, some had
rolled tails, some had changes in the skull shape that made them look more
like dogs ( Trut et al., 1991, 2009 ).
The basis of the morphological and physiological changes that occurred
in the course of selection for tame behavior in the farm fox population is
unclear. Genetic drift is plausible, as is genetic hitchhiking, especially if
genes involved in development or physiology are located on the same chro-
mosomes and in close proximity to genes involved in behavior. Selection
acting on behavioral genes would inevitably act as well on tightly linked
neighboring genes. In-phase alleles for both behavioral genes and neighbor-
ing genes on the same haplotype would be inherited together until sufficient
generations passed for the haplotype to be broken by recombination events.
Selection for rare alleles of genes involved in development and physiology
could promote the development of novel phenotypes or increase the fre-
quency of rare ones. Indeed, the higher rate of atypical phenotypes was
observed during the early stages of selection for behavior. Alternatively,
genes involved in behavior could have a pleiotroptc effect and be involved
in regulatory processes not only restricted to behavior, but that play an
important role in animal development and physiology (Belyaev, 1879; Trut,
1999, 2001; Trut et al., 2009 ). Support for this hypothesis comes from the
observation that multiple behavioral and morphological changes observed in
tame foxes are associated with delayed or truncated development ( Trut,
1999, 2001; Trut et al., 2009 ). This concept of neoteny, the retention of

pituitary