Biomedical Engineering Reference
In-Depth Information
evidence of macaques in Japan is as old as 0.6 my (
Kamei,
1969
) and the best molecular estimate of divergence of
Indian and rhesus macaques is about 0.16 mya (
Hernandez
et al., 2007
), the latter hypothesis is more plausible.
As for bonnet macaques, the low level of inherent
genetic variation in Japanese macaques as a whole,
combined with the small and unrepresentative sample of
founders of domestic colonies now being bred as subjects
for biomedical research in the USA, suggest that significant
levels of genetic diversity, especially rare alleles, have
probably been lost through founder effect, genetic drift, and
isolation from gene flow. This is consistent with the report
by Malhi et al. report of fewer rhesus macaque SNPs being
shared with Japanese macaques than with either bonnet or
pigtail macaques.
Theropithecus (gelada) and Lophocebus (grey mangabey)
relatives approximately 4 mya, still after macaque species
had already begun to diverge.
Zinner et al. (2009)
reported
marked paraphyly of the mtDNA of baboon taxa, especially
as concerns the distinction between the olive and yellow
baboons (
Newman et al., 2004
).
Newman et al. (2004)
speculated that the failure of their mtDNA phylogeny to
resolve the distinction between yellow and olive baboons as
distinct species resulted from recent hybridization between
the two taxa. Thus, the selection of samples for analysis
(e.g. if near hybrid zones) and level of confidence in their
origin can significantly influence the outcome of analyses.
The earliest mtDNA divergence of genus Papio, occurring
about 2 mya (
Newman et al., 2004; Zinner et al., 2009
), was
between a southern clade represented by chacma and kinda
baboons and a northern clade consisting of the olive,
guinea, and hamadryas baboons with subclades of yellow
baboons falling in both clades (
Zinner et al., 2009
).
By 1.5 mya, both clades began to diverge into para-
phyletic subclades, perhaps due to introgressive hybrid-
ization precipitated by fluctuating forests during changing
weather conditions in the Pleistocene. The yellow, olive,
and hamadryas baboons of eastern Africa diverged between
0.3 and 0.7 mya (
Zinner et al., 2009
). Only the kinda and
guinea baboons, which diverged approximately 0.3 and
0.1 mya, formed monophyletic mtDNA subclades within
the southern and northern clades, respectively, in that study.
As mtDNA is unable to provide clear resolution among the
five widely recognized taxa of genus Papio, multiple
nuclear markers will be required to resolve this issue.
As the range of P. hamadryas extends to Yemen and
Arabia, the closer similarity of P. hamadryas to both
P. anubis and P. cynocephalus probably results from an
ancient land bridge that connected the horn of Africa to
southwest Asia, across which many plant and animal
species migrated approximately 0.44 mya. Baboons may
have crossed this land bridge as early as 1.7 mya or as
recently as the last glacial maximum (LGM), about
20 000 ybp (
Wildman et al., 2004; Winney et al., 2004
).
The levels of genetic heterogeneity within and among the
baboon taxa cited above and based on mtDNA (
Newman
et al., 2004; Zinner et al., 2009
) are significantly less than
those based on the same region of mtDNA for different
macaque species (
Hayasaka et al, 1996
), suggesting that the
varieties of baboons are less divergent from each other than
regional populations of rhesus or longtail macaques. The
more recent studies have suggested that paraphyly in genus
Papio resulted from a very complex history of introgressive
hybridization rather than lineage sorting (
Zinner et al.,
2009
). Until further studies based on many nuclear loci
are completed, it is probably defensible to regard the
baboons as comprising a single species, P. hamadryas,
representing at least five different regional populations
or subspecies: P. h. hamadryas, P. h. anubis, P. h. papio,
Baboons
Fewer genetic studies have been conducted on pop-
ulations of baboons than macaques. Early taxonomies
based on morphology and behavior assigned baboons to
one of two species, P. cynocephalus and P. hamadryas,
the former of which was subdivided into four subspecies,
P. c. papio, P. c. anubis, P. c. cynocephalus,andP. c .
ursinus (
Buettner-Janush, 1966
). Evidence for this
bi-partite division was not found in the earliest genetic
studies, which were based on protein coding loci
(
Williams-Blangero et al., 1990
). In that study, two
clusters of species were suggested, with P. hamadryas
clustering with both P. anubis and P. cynocephalus and
P. papio and P. u r s i n u s clustering together with each
other. Systematic studies of variation in ABO phenotype
frequencies among the regional subspecies of baboons
have not been done, but, as in rhesus macaques, B and O
are reported to be the most common and least common
phenotypes, respectively, in Papio papio (
Wiener and
Moor-Jankowski, 1969
). Some rare O alleles found in
baboons derive from the A allele and others derive from
the B allele (
Diamond et al., 1997
).
More recent studies of mtDNA (
Newman et al., 2004
)
are consistent with Williams-Blangero's study, but suggest
less substructure among the five baboon varieties.
P. ursinus was the most distant of the five taxa, followed
by P. papio, then P. hamadryas, and, last, a cluster con-
taining intermixed sequences of both P. anubis and
P. cynocephylus, with no clear substructure. The authors
regard the especially close clustering of P. anubis and
P. cynocephalus as the probable result of natural intro-
gressive hybridization and estimated that the common
ancestor of all five varieties lived in the southern part of
Africa approximately 1.8 mya. However, Papio fossils as
old as 2.5 mya (
Delson, 1984
) indicate that the genus
is older than this, and
Newman et al. (2004)
estimated
that
it diverged approximately simultaneously from its
