Legacy of mutiny on the Bounty: founder effect and admixture on Norfolk Island

Abstract

The population of Norfolk Island, located off the eastern coast of Australia, possesses an unusual and fascinating history. Most present-day islanders are related to a small number of the 'Bounty' mutineer founders. These founders consisted of Caucasian males and Polynesian females and led to an admixed present-day population. By examining a single large pedigree of 5742 individuals, spanning 4200 years, we analyzed the influence of admixture and founder effect on various cardiovascular disease (CVD)-related traits. On account of the relative isolation of the population, on average one-third of the genomes of present-day islanders (single large pedigree individuals) is derived from 17 initial founders. The proportion of Polynesian ancestry in the present-day individuals was found to significantly influence total triglycerides, body mass index, systolic blood pressure and diastolic blood pressure. For various cholesterol traits, the influence of ancestry was less marked but overall the direction of effect for all CVD-related traits was consistent with Polynesian ancestry conferring greater CVD risk. Marker-derived homozygosity was computed and agreed with measures of inbreeding derived from pedigree information. Founder effect (inbreeding and marker-derived homozygosity) significantly influenced height. In conclusion, both founder effect and extreme admixture have substantially influenced the genetic architecture of a variety of CVD-related traits in this population.

European and Polynesian admixture in the Norfolk Island population

“…On the basis of genealogical information, the sample may be subdivided into two major groupings. Cohort 1 (herein termed 'Pedigree', n ¼ 324), are connected together in a single large pedigree from 11 founding males (9 'Bounty' mutineers and two Europeans who arrived in the mid nineteenth century) and six Tahitian women (Macgregor et al, 2009). The other major cohort (termed 'non-pedigree', n ¼ 258) are more recent, mainly twentieth century and largely unrelated, migrants to the Island, who were predominantly of European ancestry (generally from Australian and New Zealand).…”

“…A previous study estimated the level of Polynesian admixture for each individual in the main founder pedigree based on the genealogical structure of the pedigree itself. Estimates of Polynesian ancestry ranged from 0-45% (Macgregor et al, 2009). We compared these estimates to those derived from the set of autosomal AIMs (Figure 3).…”

“…Variation in genomic ancestry levels are the basis of 'admixture mapping' approaches, which may be appropriate in the Norfolk Island population to find the genes involved in Figure 3 Relationship between pedigree and genetic-based estimates of Polynesian Ancestry (r ¼ 0.72, Po0.05). Pedigree estimates were made in a previous study and are the fraction of each Islander's genome derived from six founding Polynesian females according to genealogical records (Macgregor et al, 2009). Genetic estimates are the proportion of each Islander's genome assigned to Cluster 2, presumed Polynesian ancestry, based on STRUCTURE analysis of 110 autosomal AIMs.…”

The Norfolk Island Eye Study (NIES): Rationale, Methodology and Distribution of Ocular Biometry (Biometry of the Bounty)

“…The first took place from 1788-1814 and the second from 1824 until the last convict settlers were transported to Tasmania in the 1850s (Hoare, 1999 The Norfolk Island Pitcairn Pedigree Norfolk Island's family history is particularly well documented, in large part because anthropologists from the island have maintained an exhaustive genealogical history in the form of a single large family pedigree spanning 250 years. In addition to Norfolk Island's obvious geographical isolation, strict immigration and quarantine legislation has restricted new founders from migrating to Norfolk Island (Macgregor et al, 2010). The main Norfolk Island Pitcairn Pedigree contains 5,742 individuals, of whom 1503 were consanguineous.…”

Pedigree Structure and Kinship Measurements of a Mid-Michigan Community: A New North American Population Isolate Identified

“…Rather, they share a number of general characteristics, such as a small founder population, rapid outgrowth, a history of isolation, an endogamous genealogy, environmental and phenotypic homogeneity, (McQuillan et al 2008). This homozygosity might contribute risk of health-related conditions (Macgregor et al 2010) and common diseases, like cardiac conditions (Ismail et al 2004;Ushasree et al 2009;Youhanna et al 2010) and some cancers (Denic 2003;Levy-Lahad et al 1995). While relatedness of parents is noted as a risk factor for common complex diseases, individuals within population isolates are at no greater risk for childhood mortality (Bittles and Neel 1994) and might share positive health attributes such as longevity (Altukhov Yu and Sheremet'eva 2000) and increased fertility (Helgason et al 2008).…”