Haldane and Hybrid Bears

Haldane's* Rule:

When in the offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterozygous (heterogametic) sex.

This rule is almost universally true (see table**) and is supported by the observations that among hybrids such as ligers, zonkeys and mules the males (XY) are all sterile while females (XX) may be fertile (though often poorly so, due to mismatched chromosome numbers, discussed briefly here). The reverse observation - sterile females - is true in species where the male is the homogametic sex such as birds and butterflies. Hypotheses explaining the genetic basis of Haldane's Rule and its challenges are explained nicely here.

Recently, a new fertile hybrid was discovered. The grizzly-polar bear hybrid has been seen before, as discussed here, and with changing habitats and more grizzly-polar bear encounters we'll likely see more. The Toronto Star is reporting the first offspring of a hybrid bear.

Researchers in the Northwest Territories say they may have found the first recorded offspring of a hybrid female polar-grizzly bear in the wild. [...] Officials with the territorial government say those test showed that the dead bear was the offspring of another hybrid bear — a female polar-grizzly mix who had mated with a male grizzly.

Given Haldane's Rule, that the hybrid parent was female isn't surprising, but it remains to be seen whether the males are sterile or if this becomes the first mammalian exception.

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*In addition to being one of the founders of population genetics, Haldane also wrote poetry about rectal cancer, a disease he succumbed to in 1964.

**Table source: Nature 355, 511-515 (1992). Ref. 41 refers to Coyne, J.A. and Orr, H.A. in Speciation and its Consequences (eds Ott, D. and Endler, J.) 180-207 (Sinauer, Sunderland, Massachusetts. 1989)

The sex files: cavemen, monkeys and beetles

Bayman recently pointed out that he finds Neanderthals sexy, and thinks that maybe different hominids experimented with interspecies sex, perhaps while in college. Yet he may not be alone with these views, some people have proposed that red hair for example was a Neanderthal trait introduced into our gene pool. One of the long-standing problem with that theory is that no hybrid bones were ever uncovered, although a recent finding in Gibraltar may change that... Still according to wikipedia:

"On November 16, 2006 Science Daily published scientific test results demonstrating that Neanderthals and ancient humans probably did not interbreed. Scientists with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the Joint Genome Institute (JGI) sequenced genomic nuclear DNA (nDNA) from a fossilized Neanderthal femur. Their results more precisely indicate a common ancestor about 706,000 years ago, and a complete separation of the ancestors of the species about 376,000 years ago. Their results show that the genomes of modern humans and Neanderthals are at least 99.5-percent identical, but despite this genetic similarity, and despite the two species having cohabitated the same geographic region for thousands of years, there is no evidence of any significant crossbreeding between the two."

Of course this makes sex with monkeys even less probable. In fact, Dave Chapelle once pointed out that AIDS could not have come from someone having sex with monkeys, because anyone who would have sex with a monkey, probably doesn't have sex with woman. Yet there has been experiments by a Russian scientist in the past:

"Dr. Il'ya Ivanov was a world-renowned expert on veterinary reproductive biology, but he wanted to do more in life than breed fatter cows. So in 1927 he traveled to Africa to pursue his vision of interbreeding man and ape. Thankfully his efforts weren't successful. To a great degree this was due to the native staff of the West Guinea research facility where he worked, from whom he constantly had to conceal the true purpose of his experiments. If they had found out what he was really doing, he wrote in his diary, "this could have led to very unpleasant consequences." The necessity of carrying out his work in secrecy made it almost impossible to do anything, although he did record two unsuccessful attempts to artificially inseminate female chimpanzees with human sperm."

He eventually tried to implant an orangutan embryo into a human womb, but the ape (Tarzan) died before the experiment could be performed, and he was sent to prison.

Still, sex with monkeys is probably more pleasant than sex with Bruchid beetles, at least for females. In this species the males unfurl an impressive penis covered with spikes and impales the female's reproductive tract. The female tries to kick the male to end copulation early and minimize damage. However she does get something out of it, she uses the copious amount of ejaculate to rehydrate and nourish herself. So the perfect female in beetles likes it quick and swallows...

In humans, kissing may also be a way for females to rehydrate: "Males, however, were more likely than females to initiate open mouth kissing and kissing with tongue contact. The researchers speculate that the exchange of saliva during kissing may have biological consequences in its own right. Male saliva contains measurable amounts of the sex hormone testosterone which can affect libido."

Zeedonks, Beefalos, & Wolphins

The title of this post is the names of some lesser known intra-specific hybrid animals (check the link for more), namely a cross between a Zebra and donkey (aka zonkey), a cattle/bison cross, and a rare cross of a False Killer Whale and a Bottlenose Dolphin. Of course, the most common and well known hybrid is the mule, a cross between a horse and a donkey. Most intra-specific hybrid animals are sterile as a result that they can not produce viable gametes through meiosis because of a lack of homologous chromosomes. Since a hybrid has one set from one animal and one set from another they don't pair up properly during metaphase, they most often also have a different number of chromosomes to begin with. Some animal hybrids are fertile however such as the female tigon.
From Napoleon Dynamite:

Deb: What are you drawing?

Napoleon: A liger.

Deb: What's a liger?

Napoleon: It's pretty much my favorite animal. It's like a lion and a tiger mixed. Bred for its skills in magic.

Napoleon dynamite was a bit of a dweeb (magic is an innate or learned ability and not a skill) but a liger is pretty awesome. Check out this video that will make you respect the liger.

I guess I was thinking about this since someone mentioned that they had heard of a cat/rabbit cross. They are mythical and probably don't exist although there are lots of breeds of rabbits that have cat like appearance. They don't exist but that's not from lack of trying.