Nature Wins Over Nurture in the Gaited Horse

Guðmundur Arnarson rides Sævar frá Stangarholti (grey with sunfading black base) in tölti at five-gait horse championships in Hella, 2008. Photo Dagur Brynjólfsson, WikiCommons

We talk very easily about “a gene for this” or “a gene for that” but most of our characteristics have more complex biological origins than a single strand of DNA. That’s perhaps why it’s such a surprise to read this story, which my brother, Sarah Everts and Christine Wilsdon all sent me.
Researchers at Uppsala University have discovered that a variation on a single gene called DMRT3 on chromosome 23 causes gves mice a fifth gait. The scientists moved on to looking at Icelandic horses, famous for their rapid “tolt” and sometimes for “pacing”. From GenomeWeb:

To look at this in more detail, the team started by doing an association study involving 30 Icelandic horses that could walk, trot, gallop, and amble or “tölt,” and another 40 Icelandic horses that could do those four and move at the two-beat pace gait.

Amongst the horses capable of pacing, the researchers found a significant association involving a region on chromosome 23. More extensive analyses indicated that five-gaited Icelandic horses typically share several SNPs in the region, including a nonsense mutation that introduces a premature stop codon in DMRT3.

When the team screened hundreds more Icelandic horses, it identified the same alteration affecting both copies of the DMRT3 gene in almost all of the five-gaited horses tested.

In Icelandic horses with four gaits — those that could tölt but did not perform the pace gait — the DMRT3 mutation was still more common than it is in many other horse breeds. But the change was far less likely to be homozygous.

The nonsense mutation in DMRT3 turned up in some other breeds too, the researchers reported, though it tended to be more common among those with uncommon gaits and in breeds developed for harness racing, consistent with the notion that DMRT3 function contributes to the way coordinated movement is controlled.

Discover Magazine has interviews with some of the scientists involved and added this, suggesting that while nature may have made the gaited horse by random mutation, it was human nurture that helped it to thrive:

By contrast, it’s absent in all horses that stick to the standard walk, trot and gallop. Thoroughbreds, Shetland ponies, wild Przewalski’s horses—all of them have unabridged DMRT3 proteins. The conclusion is stark: for a horse to move beyond its three natural gaits, it needs a stunted version of the DMRT3 protein. … [Mice with the mutation] walked normally, but the coordination between their legs broke down at high speeds.

The same is true for horses, and explains why the DMRT3 mutations are almost non-existent in the wild. Carriers find it hard to transition from trots and paces to full-blown gallops. They lack the coordination necessary to pull off the fastest gait, and predators would easily have removed them from the gene pool.

Humans were kinder, and saw a different sort of potential. Andersson imagines that early humans noticed that some horses could move in unique ways, and selected them for breeding, perhaps because they offered a smoother ride or were more versatile at intermediate speeds. Certainly, these animals also do very well in harness-racing, where trotting horses are disqualified if they break into a gallop. In our stables and tracks, an otherwise debilitating mutation has found a comfortable home.

At this point a bell went off in my head and I made my way to the bookshelf. Stephen Budiansky’s The Nature of Horses: Their Evolution, Intelligence and Behaviour. Page 21 of the Phoenix paperback:

The almost unbelievable discovery of fossil footprints of three Hipparion horses [in Tanzania]  from the middle Pliocene (3.5 million years ago) has provided ample confirmation of the speed and agility of these grasslands adapted horses.  … A subsequent analysis of the horse footprints makes a convincing case that these Hipparion horses traveled at a good clip utilizing the gait known as the running walk – the characteristic gait of Tennessee walking horses, Icelandic ponies, and paso finos, in which the length of stride is extended and only one or two feet are in contact with the ground at any given time. Comparison of the the fossil footfalls wih the footfall patterns of Icelandic ponies suggests that one of the Hipparions was traveling at 15 kilometers per hour.

Hipparions, imagined by Heinrich Harder (1858-1935) via WikiCommons

Hipparion is a relative of the modern horse, but not an ancestor. According to Wikipedia, it existed for 22.219 million years, which really ain’t bad for a runty little gaited horse.

Whole Heap of Little Horse Links

I was away! Things happened! But first – a round up of curious happenings in the horse world!

  • Looks like I got rid of the virtual racing stable I ran in the early 1990s far too early. An unraced imaginary horse from the Digiturf game has just been sold for $5,225. Yes, not only is it nonexistent, it’s also unproven. $5,225. You could get a real racehorse for a lot less. ESPN reports.
  • The Guardian’s dance critic was dispatched to review para-dressage: “With their tightly plaited manes and long ballerina necks, they perform tightly controlled pirouettes and piaffes with impressive finesse; they float across the arena with a silken stride that is like a horsey grand jeté.”
  • An Australian study suggests that Monty Roberts’ methods should be re-assessed. (Horse Talk). UPDATE: Monty responds with a link to an earlier peer-reviewed study of his methods from Anthrozoology.
  • A riding school in Kenya thrives, thanks to its enterprising owner. (BBC).
  • Yahoo has a mighty fine photo gallery of an Icelandic horse round up. Iceland: a nation where horse shoes are sold at garages. MSNBC has sulky racing on the north German coast.
  • The Bloggess brings us the worst example of equine taxidermy I’ve yet seen – and I love bad taxidermy. It’s meant to be a falabella.
  • Kazakhstan is shipping its own horse-meat sausages to London for its Olympic Team. (The Atlantic)
  • As a US Senate hearing calls for stricter rules concerning drug use in horse racing, the New York Times gets hold of Kentucky Derby winner I’ll Have Another’s vet sheet. The colt had been battling tendon problems and osteoarthritis for some time before he even began his Triple Crown bid. That’s an unsound horse, racing on dirt at the highest level. Since the NYT’s report, other racing figures have come forward to say this is no big deal and in fact, common and legitimate. (New York Times).
  • Meanwhile, here’s a less depressing NYT blog post on using dressage to train both competing and retired racehorses. (NYT)
  • Riding school ponies stolen in area of Florida notorious for blackmarket horse-meat slaughters. (CBS Local).
  • And so that we don’t end on a bum note, here’s North Korean leader Kim Jong Un’s girlfriend, Hyon Song-Wol, singing her smash hit “Excellent Horse-like Lady” or “A Girl In The Saddle Of A Steed”. Enjoy.

The Mares of Diomedes Gallop On

In Greek myth Heracles’ eighth task is to steal the flesh-eating mares of the giant Diomedes: Podagros, Lampon, Xanthos and Deinos. Heracles is victorious in the ensuing struggle with Diomedes, and feeds his body to the horses who chomp him up with much relish and gore, as in all the best Greek literature. In some versions the mares also breathe fire and you might have thought that as the horse is the herbivore incarnate, Podagros et al’s taste for flesh was as fanciful as their flaming nostrils.

Not so, it seems.

Several years ago Horse.com featured a few articles on meat-eating horses which threw up some interesting curiosities. Did you know that Icelandic horses are fed dried fish as it contains nutrients not present in the grass on the island? Or that Tibetan horses were fed sheep blood and millet gruel? More gruesome still were the accounts that readers sent in of carnivorous horses they had known, that consumed whole ducklings or murdered pigeons in their fields. Now horse historian CuChullaine O’Reilly has written a book on the subject, called Deadly Equines. Horse Talk reports:

O’Reilly said he was stunned to discover that mankind had known about meat-eating horses for at least four thousand years; that they had been known to consume nearly two dozen different types of protein, including human flesh, and that these episodes had occurred on every continent, including Antarctica.

“This wasn’t an odd example or two. This amounted to a hidden history of horses.”

O’Reilly says tales of deadly and flesh-eating horses arise in mankind’s mythology, as well as history.

“For example, mythology states that Alexander the Great’s horse, Bucephalus, was a notorious man-eater.

“Literature has Shakespeare, Steve McQueen and Sherlock Holmes all involved with man-killers or meat-eating horses. And we now know that meat-eating horses were used to explore both the Arctic Circle and Antarctica.

“The evidence is there for all to see – for those willing to do so.”

My copy has been ordered!