Abstract
The Caribbean is a genetically diverse region with heterogeneous admixture compositions influenced by local island ecologies, migrations, colonial conflicts, and demographic histories. The Commonwealth of Dominica is a mountainous island in the Lesser Antilles historically known to harbor communities with unique patterns of migration, mixture, and isolation. This community-based population genetic study adds biological evidence to inform post-colonial narrative histories in a Dominican horticultural village. High density single nucleotide polymorphism data paired with a previously compiled genealogy provide the first genome-wide insights on genetic ancestry and population structure in Dominica. We assessed family-based clustering, inferred global ancestry, and dated recent admixture by implementing the fastSTRUCTURE clustering algorithm, modeling graph-based migration with TreeMix, assessing patterns of linkage disequilibrium decay with ALDER, and visualizing data from Dominica with Human Genome Diversity Panel references. These analyses distinguish family-based genetic structure from variation in African, European, and indigenous Amerindian admixture proportions, and analyses of linkage disequilibrium decay estimate admixture dates 5–6 generations (~160 years) ago. African ancestry accounts for the largest mixture components, followed by European and then indigenous components; however, our global ancestry inferences are consistent with previous mitochondrial, Y chromosome, and ancestry marker data from Dominica that show uniquely higher proportions of indigenous ancestry and lower proportions of African ancestry relative to known admixture in other French- and English-speaking Caribbean islands. Our genetic results support local narratives about the community’s history and founding, which indicate that newly emancipated people settled in the steep, dense vegetation along Dominica’s eastern coast in the mid-19th century. Strong genetic signals of post-colonial admixture and family-based structure highlight the localized impacts of colonial forces and island ecologies in this region, and more data from other groups are needed to more broadly inform on Dominica’s complex history and present diversity.
Highlights
The Caribbean is a genetically diverse region where migrations, specific island ecologies, and colonial conflicts have locally shaped demographic patterns and population structures [1,2,3,4]
We assessed population structure in Bwa Mawego, Dominica using 468,721 single nucleotide polymorphism (SNP) genotyped in a sample of 159 people using fastSTRUCTURE [29]
The lower bound estimate of Kmax = 4 indicates that four clusters maximize the marginal likelihood of observed genetic variation, and the upper bound estimate of K = 9 accounts for additional weaker population structure in Bwa Mawego (Fig 1)
Summary
The Caribbean is a genetically diverse region where migrations, specific island ecologies, and colonial conflicts have locally shaped demographic patterns and population structures [1,2,3,4]. Mitochondrial and Y chromosome data indicate that uniquely higher proportions of indigenous Amerindian genetic lineages have survived in Dominica than among neighboring Caribbean islands, but genome-wide patterns of extant variation in Dominica have yet to be characterized [7, 8]. We assess population structure and genetic ancestry in a horticultural community on the eastern coast of Dominica using high-density single nucleotide polymorphism (SNP) and genealogical data to inform post-colonial history in this unique region with biological evidence. Indigenous lineages survive into the present through localized admixture and among distinct ethnic communities such as Santa Rosa First Peoples in Trinidad [12] and the Kalinago Territory in Dominica [5]
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