Large-scale genomic analysis reveals the genetic cost of chicken domestication.

BACKGROUND: Species domestication is generally characterized by the exploitation of high-impact mutations through processes that involve complex shifting demographics of domesticated species. These include not only inbreeding and artificial selection that may lead to the emergence of evolutionary bottlenecks, but also post-divergence gene flow and introgression. Although domestication potentially affects the occurrence of both desired and undesired mutations, the way wild relatives of domesticated species evolve and how expensive the genetic cost underlying domestication is remain poorly understood. Here, we investigated the demographic history and genetic load of chicken domestication. RESULTS: We analyzed a dataset comprising over 800 whole genomes from both indigenous chickens and wild jungle fowls. We show that despite having a higher genetic diversity than their wild counterparts (average π, 0.00326 vs. 0.00316), the red jungle fowls, the present-day domestic chickens experienced a dramatic population size decline during their early domestication. Our analyses suggest that the concomitant bottleneck induced 2.95% more deleterious mutations across chicken genomes compared with red jungle fowls, supporting the "cost of domestication" hypothesis. Particularly, we find that 62.4% of deleterious SNPs in domestic chickens are maintained in heterozygous states and masked as recessive alleles, challenging the power of modern breeding programs to effectively eliminate these genetic loads. Finally, we suggest that positive selection decreases the incidence but increases the frequency of deleterious SNPs in domestic chicken genomes. CONCLUSION: This study reveals a new landscape of demographic history and genomic changes associated with chicken domestication and provides insight into the evolutionary genomic profiles of domesticated animals managed under modern human selection.

863 genomes reveal the origin and domestication of chicken.

Despite the substantial role that chickens have played in human societies across the world, both the geographic and temporal origins of their domestication remain controversial. To address this issue, we analyzed 863 genomes from a worldwide sampling of chickens and representatives of all four species of wild jungle fowl and each of the five subspecies of red jungle fowl (RJF). Our study suggests that domestic chickens were initially derived from the RJF subspecies Gallus gallus spadiceus whose present-day distribution is predominantly in southwestern China, northern Thailand and Myanmar. Following their domestication, chickens were translocated across Southeast and South Asia where they interbred locally with both RJF subspecies and other jungle fowl species. In addition, our results show that the White Leghorn chicken breed possesses a mosaic of divergent ancestries inherited from other subspecies of RJF. Despite the strong episodic gene flow from geographically divergent lineages of jungle fowls, our analyses show that domestic chickens undergo genetic adaptations that underlie their unique behavioral, morphological and reproductive traits. Our study provides novel insights into the evolutionary history of domestic chickens and a valuable resource to facilitate ongoing genetic and functional investigations of the world's most numerous domestic animal.

Author Correction: 863 genomes reveal the origin and domestication of chicken.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Purification and characterization of extracellular phytase from a marine yeast Kodamaea ohmeri BG3.

The extracellular phytase in the supernatant of cell culture of the marine yeast Kodamaea ohmeri BG3 was purified to homogeneity with a 7.2-fold increase in specific phytase activity as compared to that in the supernatant by ammonium sulfate fractionation, gel filtration chromatography (Sephadextrade mark G-75), and anion-exchange chromatography (DEAE Sepharose Fast Flow Anion-Exchange). According to the data from sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the molecular mass of the purified enzyme was estimated to be 98.2 kDa while the molecular mass of the purified enzyme was estimated to be 92.9 kDa and the enzyme was shown to be a monomer according to the results of gel filtration chromatography. The optimal pH and temperature of the purified enzyme were 5.0 and 65 degrees C, respectively. The enzyme was stimulated by Mn(2+), Ca(2+), K(+), Li(+), Na(+), Ba(2+), Mg(2+) and Co(2+) (at a concentrations of 5.0 mM), but it was inhibited by Cu(2+), Hg(2+), Fe(2+), Fe(3+), Ag(+), and Zn(2+) (at a concentration of 5.0 mM). The enzyme was also inhibited by phenylmethylsulfonyl fluoride (PMSF), iodoacetic acid (at a concentration of 1.0 mM), and phenylgloxal hydrate (at a concentration of 5.0 mM), and not inhibited by EDTA and 1,10-phenanthroline (at concentrations of 1.0 mM and 5.0 mM). The K (m), V (max), and K (cat) values of the purified enzyme for phytate were 1.45 mM, 0.083 micromol/ml . min, and 0.93 s(-1), respectively.

Complete mitochondrial genome of Sri Lankan Junglefowl (Gallus lafayetti) and phylogenetic study.

The complete mitochondrial genomes of two Sri Lankan junglefowl (Gallus lafayetti: CJF) individuals were sequenced by using next-generation sequencing technique. Samples were collected from Rathnapura and Pelmadulla areas in Sri Lanka. The complete mitochondrial DNA is 16,839 bp in length, with a typical mitogenome structure composed of a non-coding control region, 22 tRNA, two rRNA, and 13 protein-coding genes. Overall base composition is 30% A, 23.9% T, 32.3% C, and 13.6% G indicating high content of 54.0% A + T for both individuals. Phylogenetic analysis reveals that CJF samples cluster with the clade of the green junglefowl (Gallus varius) and red junglefowl (Gallus gallus) than to grey junglefowl (Gallus sonerattii: GyJF). This result can be subsequently used to provide essential information for junglefowl evolution.