Influence of Sires on Population Substructure in Dülmen Wild Horses.

Simple Summary: Dülmen wild horses have been managed by the Dukes of Croÿ for about 180 years in the Merfelder Bruch, a region near Dülmen in Westphalia, Germany. The Dülmen wild horses are freely roaming in this area of about 1400 acres all year round without human intervention and have to cope with the harsh natural conditions. Each breeding season 2–3 stallions are employed to sire foals. Herdbook records for this herd are not available due to the wildlife living conditions, free from any human disturbances. In this present study, we analyzed the distribution of the male progeny by their sires and whether sire effects on the genetic diversity and structure in the male progeny can be found. The genetic substructure in female progeny could not be evaluated as the fillies could not be captured for sampling. The paternal half-sib groups showed a very similar genetic diversity, but pairwise genetic distances and neighbor-joining dendrograms indicated a clustering by sires and a marker variance of 9% between paternal progeny groups. Bayesian cluster analysis supported subdivision into paternal progeny groups. Cluster memberships to paternal progeny groups, which were sired in the same year but by different sires, may also be related to mares, while clusters of paternal progeny from the same sire, but in intervals of more than one year, could not be distinguished. The employment of sires which are able to withstand the harsh natural conditions may also ensure a high genetic diversity in their progeny. The objectives of the present study were to analyze the influence of the stallions employed in the Dülmen wild horses on the genetic diversity and population substructure using Bayesian cluster analysis. The Dülmen wild horse is maintained as a unique horse population exposed to the natural conditions all year round in the Merfelder Bruch near Dülmen in Westphalia, Germany. Stallions selected for breeding have to prove their abilities to survive under this harsh environment. We used multilocus genotypic information from a set of 29 autosomal microsatellites to determine the paternity of 185 male foals sired by nine stallions. As females could not be sampled, we could not make inferences on all yearlings and test whether there are differences in the genetic population parameters between both sexes. The mean number of progeny was 19.92 with a range of 2–32, caused by the length of the service period per stallion. The average observed and unbiased expected heterozygosity was 0.688 and 0.631, the mean number of alleles was 4.448, and Wright's FIS was −0.173. Pairwise genetic distances (FST and Nei's unbiased genetic distances) were significant and varied between 0.038 to 0.091 and 0.085 to 0.290, respectively. Neighbor-joining dendrogram plots clustered a large proportion of the paternal progeny groups in different branches. Posterior Bayesian analyses using seven paternal half-sib groups with 10–74 members supported a maximum of six clusters, with two paternal progeny groups not differing, and a median of five clusters, with two groups of two sires each falling into the same clusters. When sires were employed in non-consecutive years, progeny from these different years of the same sires were grouped in the same cluster, whereas the progeny of one sire from two consecutive years were in different clusters. We were able to distinguish male progeny from Dülmen wild horse stallions and to show the effects of stallion use on the genetic substructure in the Dülmen wild horse herd. In conclusion, the analyses showed the genetic potential of the Dülmen wild horse stallions to maintain a high genetic diversity and also the effects in which breeding seasons and for how long stallions are used to sire foals. The selection of stallions may be sensitive for the further development of genetic diversity and preserve this closed population as a valuable resource for further studies on the evolution of the horse. [ABSTRACT FROM AUTHOR]