Post-bottleneck mtDNA diversity in a free-living population of European bison: implications for conservation

A free-living population of European bison Bison bonasus in the Bialowieza Primeval Forest originated from only seven founder animals after a severe bottleneck that occurred at the beginning of the 20th century. Consequently, the contemporary population of the species is characterized by low genetic diversity. We studied a total of 195 individuals (127 males and 68 females). A 1429 bp fragment of mitochondrial DNA (mtDNA) including the D-loop region was analyzed in 87 individuals and revealed only three distinct haplotypes. Nucleotide (pi) and haplotype (H-d) diversity values were estimated for the European bison and were compared with pi and H-d estimated from three individuals of American bison Bison bison. Very low diversity values were found in the European bison in comparison with the diversity values found in the American bison. The low mtDNA variability in the European bison is in concordance with theoretical expectations for a species that has undergone a severe and recent bottleneck. A management strategy for the preservation of the rare and very rare haplotypes present in the Bialowieza population of the European bison is discussed. Furthermore, all 195 individuals were investigated for heteroplasmy involving these three haplotypes, in order to detect a possible association between heteroplasmy and the incidence of males affected by posthitis, a disease that affects the male reproductive organs, leading to necrotic lesions. Heteroplasmy was found in 15 females, in 17 males affected by posthitis and in 11 non-affected males, and no significant association was found.