Hey Fred!
I don't charge any fee for verbose erudite elucidation. I am so happy
when people don't yell at me that I think silence is a high compliment!
Just fasten your seat belt so if you fall asleep, you will not fall out
of your chair and injure yourself.
The genetics of the polecat group are extremely close (the "polecat
group" being the black-footed ferret, steppe polecat, and European
polecat). The latest genetic research suggests that all polecats are
the descendants of a single group of polecats that survived the ice
age (the Pleistocene) inside a single small geographic region called a
"Pleistocene Refugium." This could have been as long ago as 500,00 to
400,000 years ago, or as soon as 100,000 to 80,000 years ago. Because
of this, ALL polecats, including the domesticated ferret, are extremely
close in a genetic sense, and probably represent a single species
(Sorry Travis, but that is where the research is going and the evidence
points). So, the following statements are factual and backed with gobs
of empirical data and published works:
1. Domesticated ferrets (Mustela furo) easily breed to European
polecats (Mustela putorius). This is a "natural" breeding, can occur in
the wild, results in extremely viable offspring who can successfully
breed, and there is no evidence of breeding depression. I have held,
played with, and studied domesticated ferret (M. furo) to European
polecat (M. putorius) introgressions (M. furo x M. putorius).
2. Domesticated ferrets (M. furo) easily breed to steppe polecats
(Mustela eversmanni). This is also a "natural" breeding, can occur in
the wild, results in extremely viable offspring who can successfully
breed, and there is no evidence of breeding depression. I have held,
played with, and studied domesticated ferret (M. furo) to steppe
polecat (M. eversmanni) introgressions (M. furo x M. eversmanni).
3. European polecats (M. putorius) easily breed to steppe polecats (M.
eversmanni). This is a "natural" breeding, can occur in the wild,
results in extremely viable offspring who can successfully breed, and
there is no evidence of breeding depression. I have held and studied
European polecat (M. putorius) to steppe polecat (M. eversmanni)
hybrids (M. putorius x M. eversmanni).
4. Steppe polecats (M. eversmanni) can easily breed to black-footed
ferrets (M. nigripes). This is also a "natural" breeding, results in
extremely viable offspring who can successfully breed, and there is no
evidence of breeding depression. I have held and studied steppe polecat
(M. eversmanni) to black-footed ferret (M. nigripes) hybrids (M. furo x
M. eversmanni).
5. An older Russian publication states that black-footed ferrets can
breed with domesticated ferrets and both the steppe and European
polecat. This research came out of attempts to build a better
fur-bearer and apparently failed to produce better furred animals.
While not specifically mentioned in North American literature, it is
clear that some trade in live black-footed ferrets took place early
last century; I have seen black-footed ferret skeletons and skins in
several European countries.
6. Mid-century Russian publications on genetics basically say the
domesticated ferrets can successfully breed with black-footed ferrets
and both polecats. This era of publication seemed preoccupied with
breeding as many species to each other as possible. Domesticated
ferrets were artificially bred to mink and most other species of
weasels and polecats. Again, the underlying reason seemed ultimately
to be for fur farming.
7. Some modern North American studies have used black-footed ferret
to domesticated ferret introgressions to study disease and behavior.
These are direct crosses resulting in healthy and viable offspring.
8. Recent genetic studies suggest the genetic difference between all
polecats (remember the black-footed ferret is a polecat) is far less
than seen between wolves, reindeer, elk (red deer in Europe), moose
(elk in Europe), weasels, mink, black rats, brown rats, boar,
wolverine, badger, brown bear (grizzly bear in North America), mice,
humans, and scores of other creatures that are considered to be a
single species.
9. The main reason the polecats were separated was the difference in
the number of chromosomes. Black-footed ferrets and steppe polecats
have 38 chromosomes, while the European polecat has 40. Studies of the
domesticated ferret suggest there are also 40 chromosomes, but those
studies are flawed in that they generally looked at western European
or North American pet ferrets. Older studies --mostly Soviet -- have
suggested pet ferrets can have 38, 39 or 40 chromosomes. In any case,
the number of chromosomes is NOT the main defining characteristic of
a species. A LOT of species, including numerous rodents, rabbits,
weasels, and many other mammalian species have different numbers
of chromosomes, yet are considered a single species. The number of
chromosomes and their external appearance is called their "karyotype."
Some species have up to or more than 20 karyotypes! Obviously, the
number of chromosomes (the karyotype) do not define a species.
10. The real separation of a species is a lack of breeding although
they live in similar geographic locations (like the wolf and the
coyote, or the white-tailed deer and mule deer, who could breed but
don't normally do so). Steppe polecats will not breed naturally to
black-footed ferrets, but they are distanced by an ocean. When placed
together, these two polecats know what to do and get busy. There is
mounting evidence that European and steppe polecats produce hybrids
where they geographically overlap. There is fossil evidence that
suggest black-footed ferrets and steppe polecats made hybrids when
ocean levels and ice sheets allowed migration across the Bering Sea.
11. My study of ferret domestication suggests both the European and
steppe polecat were used to domesticate the ferret.
12. A. P. Grays 1972 book, "Mammalian Hybrids: A Check-list with
Bibliography," 2nd ed, states domesticated ferrets and polecats can
form fertile hybrids.
13. A mule is the cross between a male donkey and a female horse. A
hinny is the cross between a male horse and a female donkey. Both mules
and hinnys are typically sterile, although plenty of exceptions abound.
The sterility of mules has been attributed to the odd number of
chromosomes (mules generally have 63 chromosomes, donkeys have 62, and
horses have 64). The same is true of many mammals having an odd number
of chromosomes. For example, males with Down Syndrome are usually
considered to be sterile, although documented exceptions are known.
Lion and tiger crosses (ligers and tigons) have sterile males and
fertile females. Many of these types of hybrids are sterile, or have
sterile males.
14. However, mice (Mus musculus) frequently have chromosomal
rearrangements (Robertsonian rearrangements) that result in odd numbers
of chromosomes, yet these animals are not sterile and successfully
breed. The same seems true of scores of other species of mammals,
including black rats, various bat species, deer mice, voles, squirrels,
and many other species. Allan Wilson (1974) suggested it takes 2 to 3
million years to make enough changes to make hybrids infertile. A 2004
paper by Benjamin Fitzpatrick suggests the time necessary for hybrid
infertility is fairly accurate. Numerous papers from the 1970s and
1980s suggest a single Robertsonian rearrangement does not usually make
a hybrid infertile.
15. The main genetic difference found between the European polecat and
the steppe polecat and black-footed ferret is a single Robertsonian
rearrangement. This difference is obviously not enough to negatively
impact reproduction or viability.
Discussion: There appears to be little doubt that domesticated ferrets
and all three polecats (steppe polecat, black-footed ferret, and
European polecat) will readily interbreed to form hybrids and
introgressed crosses. There is no evidence that the offspring have any
breeding depression. It is very likely that all polecats form a single
species (ONE species) that inhabits the Holarctic (the northern
hemisphere).
There are a number of reasons why hybrid and introgressed crosses with
different chromosome numbers are infertile and there is not enough
space here to discuss them all. One thought is because in those hybrids
with odd numbers, the missing chromosome contains important information
that results in some lethal defect or male infertility. Some new
research suggests the mechanism is far more complex than that and that
" genetic distance" (the number of genetic differences added to the
genome over time) is the real mechanism behind hybrid infertility. In
short, the shorter the time between the separation of one species from
another, the less is the risk of infertility in their hybrids. So,
animals with short genetic distance, such as less than 400,000 years
with polecats, remain fertile, while those with great genetic distance,
such as 4-5 millions years with horses and donkeys, are generally
infertile.
Domesticated ferrets are probably a result of the domestication of
both polecats. Introgression of ferrets to polecats is/was common and
documented. Because of this, it is very unlikely that modern crosses
would have offspring with significant breeding depression. You have
to be careful here; domesticated ferrets have been bred to have an
increase in the number of offspring (common in domesticates), so if
the introgressed crosses drop their numbers, it should be compared to
the average offspring number in the wild species. Generally, if numbers
of offspring drop in domesticated ferret to polecat introgresions,
it is not due to a "mule effect," but rather to a loss of the traits of
domestication (I have a great Powerpoint presentation of this process
that I can show if asked to come and talk at meetings or shows).
Now, Fred, if this doesn't answer your question, nothing will!
Bob C [log in to unmask]
[Posted in FML 5747]
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