RESUMO
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.
Assuntos
Galinhas , Domesticação , Animais , Animais Domésticos/genética , Galinhas/genética , Genoma , Genômica , HumanosRESUMO
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
RESUMO
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.
Assuntos
Galinhas/genética , Genoma , Filogenia , Distribuição Animal , Animais , Animais Domésticos/genética , Ásia , Domesticação , Pool Gênico , Geografia , Funções Verossimilhança , Aves Domésticas/genética , Seleção GenéticaRESUMO
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.
