American Bison - Buffalo Field Campaign

demonstrate that Bison and Bos were genetically similar, given
molecular methods existing at the time (Beintema et al. 1986;
Bhambhani and Kuspira 1969; Dayhoff 1972; Kleinschmidt
and Sgouros 1987; Stormont et al. 1961; Wilson et al. 1985).
Additionally, the percent divergences among mitochondrial
DNA (MtDNA) sequences of Bison bison, Bos grunniens, and
Bos taurus were comparable to those calculated among other
sets of congeneric species assessed until 1989 (Miyamoto et
al. 1989). Reproductive information also supports the inference
of a close phylogenetic relationship between Bos and Bison;
Bison and some members of Bos can hybridise under forced
mating to produce partially fertile female offspring (Miyamoto et
al. 1989; Van Gelder 1977; Wall et al. 1992; Ward 2000). Species
divergence and reproductive incompatibility are evident with
the low fertility of first generation (F1) bison x cattle offspring
(Boyd 1908; Steklenev and Yasinetskaya 1982) and the difficulty
producing viable male offspring (Boyd 1908; Goodnight 1914;
Steklenev and Yasinetskaya 1982; Steklenev et al. 1986).
Behavioural incompatibility is also evident. Although mating
of bison and cattle can readily be achieved in a controlled
environment, they preferentially associate and mate with
individuals of their own species under open range conditions
(Boyd 1908; 1914; Goodnight 1914; Jones 1907). Differences
in digestive physiology and diet selection between cattle and
American bison (reviewed by Reynolds et al. 2003) and European
bison (Gębczyńska and Krasińska 1972) provide further evidence
of the antiquity of divergence between cattle and bison. Based
on palaeontological evidence, Loftus et al. (1994) concluded
that the genera Bos and Bison shared a common ancestor
1,000,000–1,400,000 years ago.
In North America, sympatry between bison and cattle is an
artefact of the recent history of colonisation by Europeans and
their livestock. However, in prehistoric Europe, the wisent (Bison
bonasus) and aurochs (Bos taurus primigeneus), the progenitor
of modern cattle, were sympatric yet evolutionarily divergent
units. The divergence in behaviour, morphology, physiology, and
ecology observed between bison and cattle is consistent with
the theory that ecological specialisation in sympatric species
occupying similar trophic niches provides a mechanism for
reducing competition in the absence of geographic isolation
(Bush 1975; Rice and Hostert 1993).
The assignment of an animal to a genus in traditional naming
schemes can be subjective, and changing generic names can
create confusion and contravene the goal of taxonomy, which is
to stabilise nomenclature (Winston 1999). However, we caution
that maintaining a stable nomenclature should not occur at
the expense of misrepresenting relationships. A change of
Bison to Bos may reflect inferred evolutionary relationships and
genetic similarities between Bison and Bos species. It could
also potentially provide continuity and stability to the scientific
reference for bison, which currently has two species names in use
(B. bonasus and B. bison). However, and in contrast, based on
divergence on a cytochrome b gene sequence analysis, Prusak et
al. (2004) concluded that although American and European bison
are closely related, they should be treated as separate species of
the genus Bison, rather than subspecies of a bison species. There
is also the potential that changing the genus from Bison to Bos
would complicate management of European (three subspecies)
and American bison (two subspecies) at the subspecies level
and disrupt an established history of public policy and scientific
community identification with the genus Bison.
Further research and debate by taxonomists and the bison
conservation community is required to reconcile molecular,
behavioural and morphological evidence before a change
in nomenclature could be supported by the American Bison
Specialist Group (ABSG). In consideration of the uncertainties
explained above, and in keeping with the naming conventions
for mammals used for the 1996 Red List and the 2008 Red List
(Wilson and Reeder 1993; Wilson and Reeder 2005), the ABSG
adheres to the genus Bison with two species, European bison
(B. bonasus) and American bison (B. bison), in this document.
3.3 Subspecies
A controversial aspect of American bison taxonomy is the
legitimacy of the subspecies designations for plains bison (B.
Bison bison) and wood bison (B. bison athabascae). The two
subspecies were first distinguished in 1897, when Rhoads
formally recognised the wood bison subspecies as B. bison
athabascae based on descriptions of the animal (Rhoads
1897). Although the two variants differ in skeletal and external
morphology and pelage characteristics (Table 3.1), some
scientists have argued that these differences alone do not
adequately substantiate subspecies designation (Geist 1991).
The issue is complicated by the human-induced hybridisation
between plains bison and wood bison that was encouraged
in Wood Buffalo National Park (WBNP) during the 1920s.
Furthermore, the concept of what constitutes a subspecies
continues to evolve.
The assignment of subspecific status varies with the organism,
the taxonomist, and which of the various definitions of
subspecies is applied. Mayr and Ashlock (1991:430) define a
subspecies as “an aggregate of local populations of a species
inhabiting a geographic subdivision of the range of the species
and differing taxonomically from other populations of the
species.” Avise and Ball (1990:59-60) adapted their definition
from the Biological Species Concept, which defines species as
groups of organisms that are reproductively isolated from other
groups (Mayr and Ashlock 1991): “Subspecies are groups of
actually or potentially interbreeding populations phylogenetically
distinguishable from, but reproductively compatible with, other
such groups.”
American Bison: Status Survey and Conservation Guidelines 2010 15