American Bison - Buffalo Field Campaign

from their original habitat near the Nyarling River in WBNP to
very different environments in the Mackenzie Bison Sanctuary
(MBS) (in 1963) and Elk Island National Park (EINP) (in 1965) do
not differ from each other, or from later specimens taken from
the original habitat (van Zyll de Jong 1986; van Zyll de Jong et
al. 1995). Furthermore, despite the passing of over 40 years,
the EINP wood bison, which live under the same conditions
as plains bison residing separately within the park, show no
evidence of morphological convergence with the plains bison
form (van Zyll de Jong 1986; van Zyll de Jong et al. 1995).
Similarly, plains bison introduced to Delta Junction, Alaska
(in 1928) from the National Bison Range (NBR) have clearly
maintained the phenotypic traits of plains bison (van Zyll de Jong
1992; van Zyll de Jong et al. 1995). Such empirical evidence
suggests that the morphological characteristics that distinguish
plains and wood bison are genetically controlled (van Zyll de
Jong et al. 1995).
Hybridisation between the subspecies in WBNP after an
introduction of plains bison during the 1920s has complicated
the consideration of subspecies designations. The controversial
decision to move plains bison from Wainwright Buffalo Park
(WBP) in southern Alberta to WBNP (from 1925 to 1928) resulted
in the introduction of domestic bovine diseases to wood bison
(Chapter 5), and threatened the distinctiveness and genetic
purity of the subspecies. In 1957, Canadian Wildlife Service
researchers discovered a presumably isolated population of
200 wood bison near Nyarling River and Buffalo Lake. The
researchers believed that this herd had remained isolated from
the hybrid herds, and therefore, represented the last reservoir
of original wood bison (Banfield and Novakowski 1960; Ogilvie
1979; Van Camp 1989). In an effort to salvage the wood bison
subspecies, bison from the Nyarling herd were relocated to
establish the MBS and EINP wood bison herds in the 1960s.
Later analysis has indicated that the Nyarling herd, and bison
elsewhere in WBNP and adjacent areas, did have contact with
the introduced plains bison (van Zyll de Jong 1986; Aniskowicz
1990), but it was minimal enough that the animals continued to
exhibit predominately wood bison traits (van Zyll de Jong et al.
1995). Studies on the impact of the plains bison introduction
have determined that the hybridisation did not result in a
phenotypically homogeneous population, as was feared (van Zyll
de Jong et al. 1995). Sub-populations within WBNP demonstrate
varying degrees of plains bison traits depending on their
proximity to, or ease of access from, the original plains bison
introduction site (van Zyll de Jong et al. 1995).
Although descriptive morphology and quantitative morphometry
provide substantial evidence supporting the subspecific
designations (van Zyll de Jong et al. 1995), early analysis of
blood characteristics and chromosomal homology did not detect
a difference (Peden and Kraay 1979; Stormont et al. 1961; Ying
and Peden 1977). Preliminary analysis of growth regulating
genes within the two subspecies suggests that the bison
subspecies have reached a stage of evolutionary divergence
due to geographic isolation (Bork et al. 1991); however, under
the Biological Species Concept, subspecies may be defined
at the next stage of speciation, that is when hybrid offspring
exhibit reduced fitness, which does not appear to be the case in
WBNP (Bork et al. 1991). Furthermore, analysis of mtDNA from
Nyarling River wood bison and plains bison did not produce
monophyletic groups (Strobeck 1991; 1992). This, however, does
not mean that there is no difference. In isolated populations,
mtDNA diverges at a rate of 1 to 2% per million years (Wilson et
al. 1985). It is estimated that the two bison subspecies diverged
approximately 5,000 years ago (van Zyll de Jong 1993; Wilson
1969), and human-induced subspecies hybridisation further
complicated the phylogeny. Therefore, current genetic analysis
techniques may not be able to detect existing differences in
the mitochondrial genome. In addition, because mtDNA is
maternally inherited, mtDNA within the Nyarling River herd, as
well as other herds in WBNP, reflects the contributions from
maternal populations, which had a biased representation of
plains bison cows (Gates et al. 2001). Therefore, the inability
to detect a difference with a molecular test comparing limited
sequences of genomic material does not necessarily mean
there is no genetic difference; it may just be beyond the current
resolution of technology.
Recent studies of DNA microsatellites indicate that the genetic
distances between plains bison and wood bison are greater
than those within either of the two subspecies (Wilson 2001;
Wilson and Strobeck 1999). The wood bison populations studied
formed a distinctive group on a Nei’s minimum unrooted tree; a
strong grouping despite the pervasive hybridisation with plains
bison (Wilson 2001; Wilson and Strobeck 1999). Wilson and
Strobeck (1999) and Wilson (2001) concluded such a strong
clustering indicates wood bison and plains bison are functioning
as distinct genetic entities, and should continue to be managed
separately. Based on the available evidence, Canada’s National
Wood Bison Recovery Team concluded: (1) historically, multiple
morphological and genetic characteristics distinguished wood
bison from the plains bison; (2) wood bison and plains bison
continue to be morphologically and genetically distinct, despite
hybridisation; and (3) wood bison constitute a subspecies of
bison, and therefore, should be managed separately from plains
bison (Gates et al. 2001).
The issue of subspecies designations is relevant to conservation
in that a decision to combine forms at the species level would
invite hybridisation and effectively eliminate any evolutionary
divergence that had occurred. Establishing definitive recognition
of bison subspecies is complicated by ongoing change of genus,
species and subspecies concepts (Winston 1999). However,
other classifications and concepts, such as the evolutionarily
significant unit (ESU; Ryder 1986), and genetic and ecological
American Bison: Status Survey and Conservation Guidelines 2010 17