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DNA and the Origin of North American Pumas
by Dr. Melanie Culver
The University of Arizona, School of Natural Resources
The puma is one of the most
geographically diverse species living
today. It occupies the largest latitudinal
range of any new world terrestrial
mammal (110 degrees in latitude), as
well as a large altitudinal range (from
sea level to 14,800 feet above sea
level). In the early 1900s, the puma
(Puma concolor) was described with
high subspecies diversity, with 32
distinctly named subspecies that were
fairly evenly distributed throughout
their broad geographical range. These
subspecies descriptions were based on
several morphological features (coat
color, pelage, skull, and skeletal measurements); however, not all specimens
compared were full adults, and
many of the subspecies were
described based on one or a few
individuals. Molecular genetic
tools provide an alternate
method to describe subdivisions
within a species and to examine
the accuracy of 32 subdivisions
for pumas.
Morphological methods
provide an important tool for
taxonomy as do molecular
genetic methods. Yet if the
incorrect marker or trait is
selected, both methods can lead
to anomalous results.
The
advantage of using molecular
markers over morphometrics is
that they allow the selection of
markers that are neutral (having
no effect on physical character-
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istics and thus not under selection) and
independent (not on the same chromosome). Neutral markers are important
because they give an indication of the
amount of time that non-interbreeding
populations have been separated; independent markers are important because
they allow acquisition of several separate lines of evidence towards a conclusion, and if most of the markers provide
the same result, it can be assumed that
the conclusion is not guided by a single
anomalous marker. Molecular genetic
markers can be used to resolve subspecies divisions, relying on the assumption that genetic changes accumulate in
a predictable manner over time. If
populations do not interbreed, given
enough time, these changes can be used
to distinguish among those populations.
Two classes of molecular genetic
markers were used to examine
subspecies-level subdivision in pumas:
DNA sequence variation for mitochondrial genes, which occur outside the
nucleus of the cell, and DNA fragment
length variation for 10 nuclear microsatellite loci. Mitochondrial sequence
variation is widely used as a genetic
marker to resolve species or
subspecies-level taxonomy, population
subdivision, gene flow, and maternal
lineage assessment. Highly polymorphic nuclear microsatellite markers are
useful to estimate relatedness among
individuals, population subdivision,
gene flow, subspecies-level taxonomy,
and can distinguish among all individuals of a species. When combined, these
markers provided 11 independent lines
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DNA and the Origin of North American Pumas
(Continued from Previous Page)
of evidence to examine subspecies
designations in pumas.
When more than 300 pumas were
analyzed, throughout North and South
America, all 11 markers were in agreement. These molecular data indicated
that South American pumas contain
high levels of genetic diversity for both
mitochondrial and microsatellite DNA.
In contrast, pumas throughout Central
and North America (north of Nicaragua) had almost no mitochondrial DNA
variation and only moderate levels of
microsatellite DNA variation. This
pattern of variation formed the basis for
establishing one puma subdivision
north of Nicaragua. The level of
genetic variation observed in South
America resulted in recognizing five
puma subdivisions south of Nicaragua.
Furthermore, the presumed boundaries
for these six groups of pumas incorporated major geographical features.
Extending from north to south within
the geographical range of pumas, the
first boundary occurs in Nicaragua
(potentially in the “lake region”), and
the other boundaries incorporate
several major rivers in South America
(Amazon River, Rio Parana, Rio
Negro, Paraguay River).
Molecular markers that are neutral
can estimate time elapsed since populations became isolated. In estimating
timing for the subdivision of puma
populations, two themes emerge; North
America is the most recently founded
population and the population inhabiting the Brazilian Highlands is the
oldest.
Additionally,
molecular
evidence indicates that pumas, as a
species, are only 390,000 years old.
Another method to estimate the timing
for species existence is the fossil
record. In the case of pumas, the oldest
fossils are approximately 300,000 years
old, remarkably similar to the molecular date; however the fossil record does
not indicate that North American
pumas are a more recent lineage (puma
fossils on both continents are equally
old). The disagreement of the North
American fossil record (which indicates equal age for North and South
American pumas) with the molecular
data (which indicates North American
to be more recent than South American
pumas), leads to the conclusion that
pumas were extirpated in North
America more recently than 300,000
years ago. If this is true then pumas in
North America today are the result of a
relatively recent re-colonization event.
The most likely timing of the extirpation would be 9,000 to 12,000 years ago
to coincide with the Pleistocene extinctions. Therefore, the North American
puma lineage may be only a few thousand years old. This presumed young
age for North American pumas is
directly related to the lack of
genetic diversity and differentiation observed in current North
American pumas. Given the potentially young age of North American
pumas, it is no surprise that genetic
analyses indicated only one subspecies in North America.
In summary, several conclusions can be made regarding subdivision and population genetics in pumas.
1) Pumas originated in the Brazilian
Highlands
approximately
300,000 years ago.
2) A
possible extirpation and re-colonization
has occurred in North America. The
potential timing of this re-colonization
event is subsequent to the most recent
ice age which ended approximately
10,000 years ago. 3) Molecular data
does not support 32 subdivisions for
pumas; instead six subspecies-level
groups are indicated. 4) Within these
six groups pumas are fairly panmictic.
These conclusions are relevant to
current conservation efforts in pumas.
Since pumas appeared to be fairly
panmictic within the six broadly
defined groups, fragmentation of habitat will drastically change the observed,
historically determined, patterns of
subdivision. Managers should strive to
maintain historical habitat connectivity
within the six large groups defined by
this data set. Additionally, managers
should take into account the revised
subspecies designations suggested by
this data set, with respect to restoration
of populations that are declining or
endangered.
© Daniel J. Cox/NaturalExposures.com
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