4.4 Targeted artificial selection during domestication ofF. chinensis
Domestication of animals was
driven by both natural and artificial selection. Under these directed
selection pressures, change in the allele frequency in specific regions
may be accumulated in the animal genome after domesticated for several
generations (Nielsen, Hellmann, Hubisz, Bustamante, & Clark, 2007). The
cultured shrimps were derived from the wild population by continuous,
high-intensity artificial selection for growth traits and is
characterized by faster growth and higher body weight than wild
individuals. Genes responsible for these characteristics may be detected
by identifying unique selection signatures in the genome. Selection
signature is characterized by the decrease in polymorphism and increase
in linkage disequilibrium in certain loci. Identification of genetic
variations by selection signature reveals the genetic mechanism of the
formation of phenotypic trait diversity during selection (Lopez, Neira,
& Yanez, 2014). In the present study, most genes with selection
signatures were identified to participate in metabolic processes.
Metabolism is the basis of growth and is related to growth rate
(Krieger, 1978; Vahl, 1984). The
changes in the allele frequency of genes related to metabolic processes
suggest artificial selection on growth. However, owing to the short
history of shrimp domestication, the genetic divergence between the wild
and cultured shrimp populations is not significant.
A pathway named the phototransduction-fly pathway was enriched by genes
with selection signatures; of the 27 background genes of this pathway,
six genes were located in the selection signature regions. This enriched
pathway signifies a visual change in domesticated shrimp.Fenneropenaeus chinensis juveniles exhibit an intense attack
behavior (P. Zhang, Zhang, Li, & Meng, 2008). We propose that the
high-density culture environment required them to develop better vision
to survive cannibalism.
Among the pathways enriched by the candidate genes, there was a pathway
related to the nervous system, neuroactive ligand-receptor interaction
pathway, which suggests that genes affecting neuronal development were
also targeted during domestication. Animal behavior is regulated by the
nervous system. Compared with aggressive animals,
docile animals survive more easily
in a culture environment (Carneiro et al., 2014; Darwin, 1860). We
speculate that tame shrimps were selected for during domestication, and
therefore the related genes were targeted.