Genetic Diversity in a Feral Horse Population from Sable Island, Canada

Abstract

The present-day Sable Island horse population, inhabiting an island off the eastern coast of Canada, is believed to have originated mainly from horses confiscated from the early French settlers in Nova Scotia in the latter half of the 18th century. In 1960, the Sable Island horses were given legal protected status and no human interference has since been allowed. The objective of this study was to characterize the current genetic diversity in Sable Island horses in comparison to 15 other horse breeds commonly found in Canada and 5 Spanish breeds. A total of 145 alleles from 12 microsatellite loci were detected in 1093 horses and 40 donkeys. The average number of alleles per locus ranged from 4.67 in the Sable Island horse population to 8.25 in Appaloosas, whereas the mean observed heterozygosity ranged from 0.626 in the Sable Island population to 0.787 in Asturcons. Various genetic distance estimates and clustering methods did not permit to support that the Sable Island horses originated from shipwrecked Spanish horses, according to a popular anecdote, but closely resemble light draft and multipurpose breeds commonly found in eastern Canada. Based on the Weitzman approach, the loss of the Sable Island horse population to the overall diversity in Canada is comparable or higher than any other horse breed. The Sable Island horse population has diverged enough from other breeds to deserve special attention by conservation interest groups.

Genetic diversity and admixture among Canadian, Mountain and Moorland and Nordic pony populations

“…The H o was highest at 0.770 in the Kerry Bog and lowest in the Exmoor at 0.569. These results are consistent with other published studies, in which fewer loci or a smaller sample size were used, for several populations including the Connemara, Fjord, Haflinger, Newfoundland, Standardbred and Sable Island (Luís et al, 2007;Plante et al, 2007;Leroy et al, 2009). In contrast, others have also found slightly higher values in the Connemara, Exmoor, Fell, Icelandic, Shetland, New Forest and Caspian (Cothran, 2004;Luís et al, 2007;Leroy et al, 2009).…”

“…These values are similar to previously reported data in which 10% to 17% and 83% to 90% of genetic diversity could be explained by breed differences and differences within individuals, respectively (Aberle et al, 2004;Glowatzki-Mullis et al, 2006;Plante et al, 2007). Individual assignment tests based on the maximum likelihood methods to predefined populations found that 98% of individuals were correctly assigned to their respective group (Tables 2 and 3).…”

“…F IS varied from 0.1291 in the Sable Island and 0.0883 in the Exmoor to 20.1215 in the Kerry Bog, indicating that there is a high deficiency in heterozygotes in the Sable Island and Exmoor populations, whereas there is an excess of heterozygotes in the Kerry Bog population. The high amounts of inbreeding seen in the Sable Island and Exmoor are likely a result of the small population sizes and feral and semi-feral status, respectively (Plante et al, 2007;Lynghaug, 2009). The combination of these two factors can lead to high levels of inbreeding and an increase in homozygosity.…”

“…The Canadian horse became very popular both within and across borders and significantly influenced the development of many of the American trotting and pacing breeds including the Standardbred, Missouri Fox Trotter, Tennessee Walking horse, Morgan, and Saddlebred (Lynghaug, 2009). Lastly, Sable Island is home to a horse population that has had no human interference since 1960 (Plante et al, 2007). Before 1960, it was not uncommon for horse breeders to release stallions on the island to breed with the feral population and then to collect the offspring and stallions the following year (Nova Scotia Museum of Nautural History, 2001).…”

“…European pony breeds (Connemara, Camargue, Landais, New Forest, Poney Français de Selle, Pottok and Welsh) clustered closely to Nordic pony breeds (Shetland, Icelandic and Fjord), but separately from both warmblood and coldblood horse breeds (Leroy et al, 2009). Despite this, large studies involving the estimation of genetic diversity of solely pony breeds have not been performed, and studies available today tend to focus only on a few breeds or compare a large number of horse breeds with only a few pony breeds; this may not be the best way to measure the genetic diversity in pony breeds (Plante et al, 2007;Behl et al, 2008;Leroy et al, 2009).…”