Re: dog breeds: same species or not

"*Hemidactylus*" <ecphoric@xxxxxxxxxxx> wrote in message
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On Dec 8, 5:51 am, "Cj" <C...@xxxxxxxx> wrote:
"*Hemidactylus*" <ecpho...@xxxxxxxxxxx> wrote in message

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On Dec 7, 1:14 pm, r norman <r_s_norman@xxxxxxxxxxxx> wrote:
On Fri, 7 Dec 2007 09:47:26 -0800 (PST), Yakov <iler...@xxxxxxxxx>
wrote:

As an argument against evoluiton, it was pointed out that
with all massive human activity at breeding animals and plants,
no new species was ever created as a result of domestication and
artificial breeding.

I want to ask: large dogs like St.Bernads, and smallest dogs like
Chihuahua... can they mate naturally between themselves, can they ?

I think they can't, based on their enormous size difference.

Does this not make them different species -- large dogs vs small
dogs ?
Ability to mate is most important aspect of a telling species apart,
no ?

This is a perennial puzzler except to biologists who know that the
ability or inability to mate has to be interpreted. Two males must be
of different species because they are not able to mate and produce
viable offspring, right? Not at all.

If you removed all intermediate breeds of dogs, then the two extremes
might well be considered different species. However the dog group
"freely" interbreeds except for extremes. So if a St Bernard breeds
with an intermediate size mutt and so does a Chihuahua, the offspring
of these two matings could freely breed thus completely mixing all the
alleles in the gene pool. That is what is important: the gene pool
is not divided into separate non-mixing groups. It takes some
intermediate steps to ensure thorough mixing, but let all dogs loose
in one place and they would all quickly merge.

Different genera of sea turtles apparently have no qualms about odd
matings, although I'm not sure how much alcohol was involved:

http://jhered.oxfordjournals.org/cgi/content/abstract/86/4/262

This proves that sea turtle "species" are actually breeds artifically
selected as pets by ancient aquatic apes, before Atlantis disappeared.

Either that or dog breeds are incipient species, But just give a male
Yorkshire terrier a stool to stand on and he'll mate with just about
anything. Your leg is fair game if you're not careful. Male dogs are
quite determined and resourceful.

A friend's female chihuahua got knocked up by a pit bull and had one
puppy years ago. Coolest little *** I ever met. Built like a pit
bull, but the size of a chihuahua.

That's a common result of a significant mismatch between breeds, few or
stillborn pups. The viability of many different size crosses is often
reduced.

Has this been supported by any hard evidence? What are the reasons for
viability reduction? Are there genetic programs with mutually
exclusive or at least unintegratable objectives? Are the internal
organs mismatchd to each other wrt size or their space alottment, like
an oversize heart not fitting within a tiny rib cage. Or does a
developing fetus tend to self-regulate and compensate for the
variations in genetic propensities coming from a large vs. small
parent? Why specifically is there a problem, if any? Is any outcome
seen as few or stillborn pups *significantly* different than what
would have been seen given a pure bred match within each breed? Or is
this anecdotally based assumpion?

I am not certain about all situations but I interact with many dog breeders
and size mismatched crosses are often a problem with accidental matings.
It's a more significant problem with older bitches where their metabolism
seems to promote irregular growth in the pups; something akin to diabetes
or lack of control of glucose. Frequently with a smaller litter (the rule
in older dogs) there will be one pup that is very much larger than the
others and parturition is often lethal for both the bitch and her pups.
Seemingly the best results occur within breed matings although few breeders
will risk breeding an older dog (over 7 or 8 years old) because of pup size
mismatches. Bitches that have unusually small pups (small breed sire) often
lose them after they are born, frequently by lying on them and causing
suffocation.

Does uterine size space set a limit for # of crossbred pups if the
female is small, so even if several eggs get fertilized only one fetus
can find room to grow. Is there some sort of mechanism that sets the
upper limit determined by puppy size?

Normal healthy young bitches, when bred with a male of the same or similar
sized breed usually have normal litters although the number of pups is
frequently limited by breed. Older bitches commonly produce smaller litters
with fewer healthy pups and apparently have problems with metabolic control.
Another problem with random mating is the fact that a litter can have to
two sires and if they are different sized males the offspring of the smaller
male are at greater risk for mortality.

I wonder if the cross was a chihuahua male and pit bull female there
would be a larger litter number. The result I saw, pit bull male and
chihuahua female produced one pup. Not sure if that's gonna be the
average number of pups for that cross or what the average litter size
for chihuahua pure crosses is vs. pit bull pure crosses would be.. The
example I gave was a single anecdotal case.

As I mentioned above size mismatched breedings often have very small litters
(<3) and there is a chance of abnormal growth (one oversize pup or several
undersized pups). I suspect dog breeds at the extreme size ranges
(Chihuahuas and mastiffs) normally have smaller litters.

Also as a rule wild dogs from dingoes and Deccan red dogs through domestic
mongrels are very much smaller animals than wolves.
In wolves (those species that have survived) there is a north/south size
cline with the northernmost animals being much larger. I'm reasonably
certain that there are geographic size differences in coyotes as well.

There is very little evidence in the wild that dog/wolf or coyote/wolf
crosses occur naturally. Wolves throughout their range will prey on dogs
and coyotes without hesitation. Coyotes are a danger to smaller dogs
throughout their range and in New England and parts of southern Canada dogs
will prey on coyotes with some regularity. These animals are cross fertile
but, like lions and tigers, crossing invariably occurs in captivity rather
than in the wild.
Cj

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