Abstract
The domestic water buffalo is native to the Asian continent but through historical migrations and recent importations, nowadays has a worldwide distribution. The two types of water buffalo, i.e., river and swamp, display distinct morphological and behavioral traits, different karyotypes and also have different purposes and geographical distributions. River buffaloes from Pakistan, Iran, Turkey, Egypt, Romania, Bulgaria, Italy, Mozambique, Brazil and Colombia, and swamp buffaloes from China, Thailand, Philippines, Indonesia and Brazil were genotyped with a species-specific medium-density 90K SNP panel. We estimated the levels of molecular diversity and described population structure, which revealed historical relationships between populations and migration events. Three distinct gene pools were identified in pure river as well as in pure swamp buffalo populations. Genomic admixture was seen in the Philippines and in Brazil, resulting from importations of animals for breed improvement. Our results were largely consistent with previous archeological, historical and molecular-based evidence for two independent domestication events for river- and swamp-type buffaloes, which occurred in the Indo-Pakistani region and close to the China/Indochina border, respectively. Based on a geographical analysis of the distribution of diversity, our evidence also indicated that the water buffalo spread out of the domestication centers followed two major divergent migration directions: river buffaloes migrated west from the Indian sub-continent while swamp buffaloes migrated from northern Indochina via an east-south-eastern route. These data suggest that the current distribution of water buffalo diversity has been shaped by the combined effects of multiple migration events occurred at different stages of the post-domestication history of the species.
Highlights
The domestic water buffalo Bubalus bubalis (Linnaeus, 1758) is native to the Asian continent
All the samples were collected during routine veterinary checks and in compliance with local/national laws and ethical rules in force at the time of sampling in the countries participating to the International Water Buffalo Genome Consortium (IWBGC)
The higher values of heterozygosity observed in Murrah and Nili-Ravi (RIVPK_NIL, HO =0.417; RIVPH_IN_MUR, HO =0.412) may have been influenced by Ascertainment Bias (AB), since these breeds were among those included in the single nucleotide polymorphism (SNP) discovery panel
Summary
The domestic water buffalo Bubalus bubalis (Linnaeus, 1758) is native to the Asian continent. Cytogenetic (chromosome number: river 2n = 50, swamp 2n = 48) and behavioral traits, the two types have traditionally had different purposes and geographical distributions (Cockrill, 1974; Borghese, 2011). More recently river buffaloes have been imported to eastern Asia, southern America and central Africa to improve milk production (Cockrill, 1974; Kierstein et al, 2004). The swamp buffalo has primarily been used for draught power in a wide area ranging from eastern India (Assam region), through southeastern Asia, Indonesia to eastern China (Yangtze River valley; Zhang et al, 2016), and was recently introduced (20th cen.) into Australia and southern America (Cockrill, 1974). There are no formally recognized swamp buffalo breeds, but regional populations are subdivided into types based on local adaptation or geographical distribution (Qiu, 1986)
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