Apple #257: Cross-Bred Animals

A few months ago, Daily Apple reader Lily Anne wanted to know about mules and donkeys and what was the difference between them, and what combinations of animals yielded which hybrids. In my entry, I provided a list of various animals that are bred with horses or ponies or zebras and the resulting combinations (zedonk being my personal favorite). However, I didn't realize that the true focus of Lily Anne's curiosity was a far more complicated question.

She wanted to know not only about all the varieties of horse-type animals, but a much larger question, which is, why is this possible with horses and horse-type animals? Does cross-breeding happen with other animals? It seems like when you mate two breeds of dogs together, this isn't on the same order of magnitude, but why is that?

Very good questions, all. I had to look into this topic a fair amount before I got a grasp on it myself.

• Mating dogs of different breeds is less dramatic. Most breeds of dogs are very similar genetically since they are all part of the same species (Canis familiaris). So it's relatively easy to get the genes of, say, a cocker spaniel to mix with, say, a poodle (with this, you get cockapoo).

This cockapoo has the markings of a cocker spaniel,
but the fur texture and non-sneeze factor of a poodle.
(Photo from Pet Works)

• Breeding a horse with a donkey, however, is a different thing. This is because the two animals are members of different species (Equus caballus plus Equus asinus, respectively).

• In most cases, you won't be successful if you try to get animals of two different species to breed. Elephant plus wildebeest simply won't work. Catfish plus camel -- well, that's just ridiculous.

• But in the case of two species that aren't obviously ridiculous combinations, even if you took the two animals out of their usual habitats and put them in the same room together, thus overcoming whatever geographic or behavioral barriers that might naturally exist between the two, and then if you artificially inseminated one with the juice of the other, in most cases, it wouldn't take. The genetic differences between the egg of one and the sperm of the other would be too great for the egg to get fertilized and remain viable.

• However. In some cases, among some species, breeding across species lines, or cross-breeding, does happen. It occurs more commonly -- and successfully -- in captivity where people can oversee and assist during all parts of the process, from insemination through weaning and rearing the young. But cross-breeding has also happened in the wild.

• Often, the resulting hybrids have genetic disorders of various kinds, or they may be infertile. They may also be susceptible to diseases that their non-hybrid parents may be able to resist. But sometimes the hybrids do survive -- and not only that, sometimes they flourish and also help the populations of both their parent species thrive.

This is a liger (son of a male lion and female tiger). His name is Hobbs.
He has a mane and roars like a lion. And, like a tiger,
he has stripes and enjoys swimming.
He can't chuff, though, the way a tiger does.
(Photo from Ligers and Tigons)


The table I've created below lists animal hybrids that I've encountered in my brief foray around this-here internet. I'm sure there are more combinations than what I've listed. It's also important to note that I have focused on mammals. There are myriads of combinations among birds, among fish, and even more among plants, and who knows how many among insects.

In this table, I've indicated the name of the resulting hybrid, if one was noted. In most cases, people named the hybrid if it was born in captivity. Also, some animals have been bred in captivity (wolf plus coyote combinations, for example), and scientists have also discovered similar combinations breeding in the wild (a species of wolf mating with coyotes).

Hybrids Born In Captivity
Species One	Species Two	Hybrid
Dog	Wolf	Wolf-dog
Dolphin	"false killer whale" (orca?)	Wholphin
Cattle	Buffalo	Beefalo
Lion	Tiger	Liger / Tigon
Leopard	Lion	Leopon
Grizzly bear	Polar bear	Grolar / Pizzly
Camel	Llama	Cama
Tamworth pig	Wild boar	Iron age pig
Horse, female	Donkey, male (jack)	Mule
Horse, male	Donkey, female (jenny)	Hinny
Zebra	Any equine	Zebra hybrid
Zebra	Horse, male	Zorse
Zebra	Pony	Zony
Zebra	Donkey	Zedonk
Golden Pheasant	Lady Amherst Pheasant
Florida panther (endangered)	Texas cougar
Wolf	Coyote
Cross-Breeding in the Wild
Species One	Species Two	Hybrid
Grizzly bear	Polar bear	Grolar / Pizzly
Wolf	Coyote
Coyote	Dog
White-tail deer	Mule deer
Cattle	Bison
Cattle	Yak

Sources
Mark Derr, "Crossbreeding to Save Species and Create New Ones," July 9, 2002
MadSci Network, Genetics, cross breeding posted by Michael Onken, May 30, 1996
"Cross-species Mating May Be Evolutionarily Important and Lead to Rapid Change, Say Indiana University Researchers," Science Daily, August 8, 2003
"What are the ramifications for wildlife of cross breeding species..." emagazine.com, week of July 24, 2005
Hemmy.Net, Top 10 Hybrid Animals, June 19, 2006
Fact Monster, Hybrid Animals