Greger Larson | bioRxiv Science

bioRxiv2016

Origin and phylogenetic status of the local Ashanti Dwarf pig (ADP) of Ghana based 1 on evidence from mtDNA analysis, MC1R, and Y-chromosome haplotypes

The Ashanti Dwarf Pig (ADP) of Ghana is an endangered pig breed with hardy and disease resistant traits. Characterisation of animal genetic resources provides relevant data for their conservation and sustainable use for food security and economic development. We investigated the origin and phylogenetic status of the local ADP of Ghana and their crosses with modern commercial breeds based on mtDNA, MC1R and Y-chromosome sequence polymorphisms, as well as genome-wide SNP genotyping.\n\nThe study involved 164 local pigs sampled from the three agro-ecological zones of Ghana. Analyses of the mitochondrial D-loop region and Y-chromosome sequences revealed both European and Asian genetic signatures, with differences between the geographical zones. Black coat colour is the most predominant within the breed, with dominant black MC1R alleles of both Asian and European origin contributing. European alleles for spotting are present at a low frequency in the sample set, and may account for the occurrence of spotted piglets in some APD litters. PCA analysis of SNP data revealed a strong location and breed effect on clustering of local Ghanaian pigs. On a global level, Ghanaian local pigs cluster closely with European pigs of commercial origin, such as the Large White.\n\nThe presence of both European and Asian contributions, with differences between geographical zones probably reflects trading and colonial influences.. Understanding the effects of admixture on important adaptive and economic traits of the ADP and other local breeds in Africa is critical for developing sustainable conservation programmes to prevent the decline of these genetic resources.

Genomics↗

bioRxiv2014

Analyses of Eurasian wild and domestic pig genomes reveals long-term gene-flow during domestication

Traditionally, the process of domestication is assumed to be initiated by people, involve few individuals and rely on reproductive isolation between wild and domestic forms. However, an emerging zooarcheological consensus depicts animal domestication as a long-term process without reproductive isolation or strong intentional selection. Here, we ask whether pig domestication followed a traditional linear model, or a complex, reticulate model as predicted by zooarcheologists. To do so, we fit models of domestication to whole genome data from over 100 wild and domestic pigs. We found that the assumptions of traditional models, such as reproductive isolation and strong domestication bottlenecks, are incompatible with the genetic data and provide support for the zooarcheological theory of a complex domestication process. In particular, gene-flow from wild to domestic pigs was a ubiquitous feature of the domestication of pigs. In addition, we show that despite gene-flow, the genomes of domestic pigs show strong signatures of selection at loci that affect behaviour and morphology. Specifically, our results are consistent with independent parallel sweeps in two independent domestication areas (China and Anatolia) at loci linked to morphological traits. We argue that recurrent selection for domestic traits likely counteracted the homogenising effect of gene-flow from wild boars and created \"islands of domestication\" in the genome. Overall, our results suggest that genomic approaches that allow for more complex models of domestication to be embraced should be employed. The results from these studies will have significant ramifications for studies that attempt to infer the origin of domesticated animals.\n\nSignificance StatementThough animal domestication has traditionally been viewed as a human-directed process involving small populations of domestic animals and limited interbreeding between wild and domestic forms, but recent zooarcheological insights have questioned this model. By studying domestication in pigs, we demonstrate that complex models of domestication incorporating long-term gene-flow from multiple wild boar populations fit genomic data from modern wild and domestic pigs significantly better than models based on the traditional perspective. In addition, we demonstrate that selection at genes associated with domestic traits countered the effects of the gene flow, thus allowing morphological and behavioural differentiation between wild and domestic populations to be maintained.

Evolutionary Biology↗