Behavioral Genetics and Animal Domestication - Genetics and the Behavior of Domestic Animals - page 60

identified, but determining the critically important genes from those which
are due to downstream changes of such key regulators can be extremely compli-
cated ( Verdugo et al., 2010 ).
Merging both a top-down and a bottom-up approach, expression QTL
(eQTL) analysis uses a combination of expression microarrays run on each
individual from a standard QTL study ( Gibson and Weir, 2005 ). In essence,
the microarray gene expression values are used as phenotypes to be correlated
with the genotypic marker information for each individual. The difference
here is that the physical position of the gene is known, so what is mapped is
the causative element leading to variation in the gene expression. Obviously,
the same issue with tissue and time point choice is still present, but this does
allow the correlation with a behavioral phenotype, which can be much more
persuasive evidence of causative gene identification ( Mehrabian et al., 2005 ).
On a note regarding model organisms (Drosohila, C.elegans, mice, etc.),
though these model systems may obviously be less directly relevant to
domestic animals (especially in the case of Drosophila and C.elegans), the
number of actual known mutations that affect behavioral traits is extremely
low, and the vast majority (indeed virtually all) of the mutations that have
been identified have been done so in these model organisms. They therefore
represent a powerful resource of what one should expect and what systems
may be involved in genes affecting behavioral variation in domestic animals.
The greater availability and more advanced genomic tools present in these
model organisms also make it useful to more finely dissect any putative
candidate genes that affect domestic animals.
EFFECTS OF SPECIFIC MUTATIONS
Social Aggregation in C. Elegans
The identification of the actual mutations that lead to variation in behavior
have been notoriously hard to identify, whilst none have been truly identified
for domestication behavior in a domestic animal. Having said that, the lessons
learnt from the few examples identified in model organisms can give impor-
tant insights to the type and effect such mutations will no doubt have.
Beginning with social aggregation, one of the classical examples for this
actually comes from the nematode C. elegans. In the wild, there are two
naturally occurring variants of worms feeding on E. coli—social and solitary
foragers ( de Bono and Bargmann, 1998; Hodgkin and Doniach, 1997 ).
Greater than 50% of social foragers are found in groups, while less than 2%
of solitary foragers are found in such states, irrespective of age and sex.
The social foragers move more rapidly ( de Bono and Bargmann, 1998 ), and
accumulate at the richest food regions. However, social foragers do not
aggregate in the absence of food ( de Bono and Bargmann, 1998 ), implying
that ecological factors are also important to the manifestation of this behavior.