High-Level Gene Flow Restricts Genetic Differentiation in Dairy Cattle Populations in Thailand: Insights from Large-Scale Mt D-Loop Sequencing

SIMPLE SUMMARY: Domestication and artificial selection lead to the development of genetically divergent cattle breeds or hybrids that exhibit specific patterns of genetic diversity and population structure. Development of mitochondrial markers has allowed investigation of cattle diversity worldwide; however, an extensive study on the population-level genetic diversity and demography of dairy cattle in Thailand is still needed. Reduction in the genetic diversity of livestock also decreases the species resilience and adaptability to local environmental conditions and disease outbreaks, thus leading us to hypothesize that Thai dairy cattle populations are approaching a status of low genetic variability. In the present study, the genetic diversity and structure of Thai dairy cattle populations were investigated, both within and between populations, for 179 individuals from nine provinces of Thailand. Mitochondrial D-loop sequence data were collected and analyzed. To minimize the degree of relationship among individuals, cattle were randomly selected based on details interviewed with the owners. The results will facilitate an improved understanding of the fundamental elements involved in breeding strategies and promote sustainable livestock utilization. ABSTRACT: Domestication and artificial selection lead to the development of genetically divergent cattle breeds or hybrids that exhibit specific patterns of genetic diversity and population structure. Recently developed mitochondrial markers have allowed investigation of cattle diversity worldwide; however, an extensive study on the population-level genetic diversity and demography of dairy cattle in Thailand is still needed. Mitochondrial D-loop sequences were obtained from 179 individuals (hybrids of Bos taurus and B. indicus) sampled from nine different provinces. Fifty-one haplotypes, of which most were classified in haplogroup “I”, were found across all nine populations. All sampled populations showed severely reduced degrees of genetic differentiation, and low nucleotide diversity was observed in populations from central Thailand. Populations that originated from adjacent geographical areas tended to show high gene flow, as revealed by patterns of weak network structuring. Mismatch distribution analysis was suggestive of a stable population, with the recent occurrence of a slight expansion event. The results provide insights into the origins and the genetic relationships among local Thai cattle breeds and will be useful for guiding management of cattle breeding in Thailand.