Genetic status of the European bison Bison bonasus after extinction in the wild and subsequent recovery

Abstract

1. The European bison Bison bonasus went through a severe bottleneck and became extinct in the wild 90 years ago. The lowland subspecies B. b. bonasus is the only one of three original subspecies that exists today. The entire species derives from only 12 founders, including a bull of the Caucasian subspecies B. b. caucasicus. Due to its presence among founders, there are two geographically separated genetic lines of European bison: the pure lowland (Białowież a) line and the hybrid lowlandCaucasian line. 2. The lowland line of the European bison originates from only seven founders with an extremely varying genetic contribution. Approximately 80% of the genes in contemporary populations come from just two founders. 3. A variety of genetic markers (mtDNA, microsatellites, single nucleotide polymorphism microchips) were applied to studies of the level of depletion of genetic variability in European bison. 4. The lowland line of the European bison, the most extensively studied, shows very low levels of genetic variation, and has just half the microsatellite heterozygosity of the closely related American bison Bison bison. The effective population size (Ne) for the highly genetically homogenous lowland line in the Polish part of the Białowieża Forest is estimated to be 23.5, far less than the census population size of 450. 5. The average inbreeding level in lowland bison is almost 50%, although no signs of inbreeding depression have been observed. In contrast, inbreeding effects have been noticed in the lowland-Caucasian line, which has a much lower average inbreeding level (28%). In spite of the apparently high fitness of the lowland bison, the lack of genetic variation and high level of inbreeding may present substantial threats in the future, especially in the context of potential epizootics.

Novel Graphical Analyses of Runs of Homozygosity among Species and Livestock Breeds

“…In particular, the ROH for the bison is extremely high for the intervals 1–5 Mb and 5–10 Mb with several regions that are completely fixed. This appears consistent with an estimated N E of 23 and a total of seven founders for the European bison's Lowland population [18]. In comparison, a recent survey presented considerably larger but variable census population size ( N C ) and N E for some of the cattle breeds included in our study [21].…”

“…For the European bison, however, large regions of the genome had a 100% (or near 100%) frequency of SNPs falling within a ROH. This suggests high levels of inbreeding, which is consistent with earlier studies and known population history involving a severe bottleneck [17, 18]. However, even limited inbreeding can cause detrimental effects [1, 19] and should be monitored.…”

“…Our study compared cattle with one related wild species, the European bison. However, this species is highly inbred and has low genetic diversity [18]. Study of other wild-domestic species pairs may therefore provide a more nuanced picture of genomic regions under selection, for example, in domestic pigs and wild boar, or captive and free-living populations of the wild boar (e.g., [24]), thus taking advantage of recent developments in high-density genomic arrays to investigate domestic and wild species (e.g., [25]).…”

Movements of European bison (Bison bonasus) beyond the Białowieża Forest (NE Poland): range expansion or partial migrations?

“…Expansion to the north will allow for connection of Białowieża population with the neighbouring herd in Knyszyn Forest and create a compact distribution range with free migrations (Pucek et al 2004). It may help to maintain genetic variability of the population, which is very low due to the bottleneck effect the bison experienced during their extermination in the wild and restoration from a small founder population (Tokarska et al 2009, 2011; Wójcik et al 2009). Grounds southwest of the Białowieża Forest offer a mosaic of woodlands and meadows and may serve as a suitable area for conflict-free population expansion.…”

Pattern of parasite egg shedding by European bison (Bison bonasus) in the Białowieża Primeval Forest, Poland

“…The bison population in the Białowieża Primeval Forest (BPF) is the largest in the world (965 individuals in total in the Polish and Belarusian parts of the Forest), and it constitutes the core of the global population of the species (29 % of free-ranging bison). Apart from lack of connectivity between isolated populations and their small size, the other threats to bison are low genetic variation due to a severe genetic bottleneck (Tokarska et al 2011), as well as diseases and parasites (Pucek et al 2004). Although bison are traditionally managed in forest habitats, increasing evidence shows that bison are a refugee species adapted to open and mixed habitats (Kerley et al 2012;Bocherens et al 2015).…”