American Bison - Buffalo Field Campaign

and their wild relatives), and Bison (bison) (Wall et al. 1992;
Wilson and Reeder 2005). Studies of nuclear-ribosomal DNA
(Wall et al. 1992), mitochondrial DNA (Miyamoto et al. 1989;
Miyamoto et al. 1993), and repetitive DNA sequences (Modi et
al. 1996) within this tribe have revealed that the genus Bos is
paraphyletic with respect to the genus Bison. Mitochondrial DNA
studies do not support the traditional organisation of the tribe
Bovini because the yak (Bos grunniens) is more closely related
to bison than to its congener cattle (Bos taurus) (Miyamoto et al.
1989; Miyamoto et al. 1993). Ribosomal DNA studies have not
fully clarified this relationship (Wall et al. 1992). However, skeletal
analysis by Groves (1981) noted that bison and yak have 14
thoracic vertebrae while other members of the Tribe Bovini have
only 13, underscoring the importance of considering heritable
morphological differences that may not be revealed using
molecular methods.
A comparison of various phylogenetic trees for the tribe Bovini
further illustrates the naming conflict. Figure 3.1(a) depicts a
Figure 3.1 Comparison of phylogenetic hypotheses for the tribe Bovini based on: (a) conventional morphological analysis (Bohlken 1958); (b) cladistic
analysis of cranial characteristics (Groves 1981); (c) mtDNA sequences (Miyamoto et al. 1989); and (d) ribosomal DNA analysis (Wall et al. 1992).
14 American Bison: Status Survey and Conservation Guidelines 2010
conventional scheme based on morphological characteristics
(Bohlken 1958), while Figures 3.1(b-d) show different
interpretations based on cranial or genetic evidence. Although
non-conventional schemes do not share identical branching
patterns for every species, the position of Bison within the pattern
of development for each alternative is equally incongruous. In the
conventional scheme, Bos branched off the tree later than Bison;
however, the arrangements based on more recent evidence
suggest that a Bos branch was followed by Bison, then by Bos.
Each alternative demonstrates that Bos is paraphyletic because
it is lacking one of its descendant branches (denoted as Bison).
Under a phylogenetic scheme, bison would be included in the
Bos clade to correct this incongruity.
For four decades, there have been suggestions to combine
Bison and Bos into one genus (Baccus et al. 1983; Gentry 1978;
Groves 1981; Miyamoto et al. 1989; Modi et al. 1996; Stormont
et al. 1961; Van Gelder 1977). Studies of DNA, blood types,
and chromosomal, immunological, and protein sequences