Dopamine Receptor Genes and Evolutionary Differentiation in the Domestication of Fighting Cocks and Long-Crowing Chickens

Abstract

The chicken domestication process represents a typical model of artificial selection, and gives significant insight into the general understanding of the influence of artificial selection on recognizable phenotypes. Two Japanese domesticated chicken varieties, the fighting cock (Shamo) and the long-crowing chicken (Naganakidori), have been selectively bred for dramatically different phenotypes. The former has been selected exclusively for aggressiveness and the latter for long crowing with an obedient sitting posture. To understand the particular mechanism behind these genetic changes during domestication, we investigated the degree of genetic differentiation in the aforementioned chickens, focusing on dopamine receptor D2, D3, and D4 genes. We studied other ornamental chickens such as Chabo chickens as a reference for comparison. When genetic differentiation was measured by an index of nucleotide differentiation (N ST) newly devised in this study, we found that the NST value of DRD4 for Shamo (0.072) was distinctively larger than those of the other genes among the three populations, suggesting that aggressiveness has been selected for in Shamo by collecting a variety of single nucleotide polymorphisms. In addition, we found that in DRD4 in Naganakidori, there is a deletion variant of one proline at the 24th residue in the repeat of nine prolines of exon 1. We thus conclude that artificial selection has operated on these different kinds of genetic variation in the DRD4 genes of Shamo and Naganakidori so strongly that the two domesticated varieties have differentiated to obtain their present opposite features in a relatively short period of time.

Mutations in the Mitochondrial ND1 Gene Are Associated with Postoperative Prognosis of Localized Renal Cell Carcinoma

“…In this study comprising 62 Japanese patients with RCC, we investigated the ND1 gene using the nucleotide differentiation index ( N ST ) [24]. As controls, ND1 sequences of 62 healthy Japanese subjects were obtained from GenBank.…”

“…For N ST analysis, nucleotide sequences of the ND1 gene of 62 subjects in this study were aligned by ClustalW using the Molecular Evolutionary Genetics Analysis (MEGA, version 6, Tempe, AZ, USA, Pennsylvania, USA, Tokyo, Japan) software [24,44]. Common sites in all sequences with gaps were excluded from analysis.…”

“…N STij for the i -site and the j th subpopulation was defined for the N ST analysis (Table S2). The N ST formula was as follows [24]: $N_{STij}=\frac{H_{Ti}-H_{Sij}}{H_{Ti}}$…”

Analysis of the source of aggressiveness in gamecocks

“…Moreover, T44I and Q232R of ADRβ2 have been detected in other Galliformes members using the molecular phylogeny analysis. We could not confirm these mutations in the wild type (G. gallus) used in our previous study 1,7 .…”

“…As Japanese ornamental chickens phenotypically differ from each other, intensive artificial selection may have been conducted before these varieties diverged from ancestral Shamo in Okinawa 2,6 . We also investigated the degree of genetic differentiation among Shamo chickens by focusing on the genes encoding dopamine receptors D2, D3, and D4 in domesticated chicken populations 7 . The dopamine receptors receive the neurotransmitter when it is released from presynaptic nerve terminals.…”