Your Thanksgiving Turkey Is in Danger of Poor Genetic Diversity From Overbreeding

Domestic turkeys originated from Mexican wild bird thousands of years ago, but now, like the Cavendish banana, they could become vulnerable to extinction.

Ruth Schuster
Ruth Schuster
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A broad-breasted Bronze turkey tom: This subspecies was selected for size and is now bred chiefly through artificial insemination, because the oversize tom is likely to squash his mate to death.
A broad-breasted Bronze turkey tom, who could be a serious danger to his mate merely by virtue of his weight. Credit: Lupin, Wikimedia Commons
Ruth Schuster
Ruth Schuster

Turkey dinner is a staple for Thanksgiving, never mind that the bird Americans love to gobble today didn't come from Turkey, and that it isn't turkey, at least as God/evolution made the bird.

The domestic turkey being roasted or fried nationwide in America this week originated from the south Mexican turkey, after some 3,000 years of husbandry that changed it radically from the original bird.

Intense selection by farmers for convenient characteristics like big breasts led today's bird to become genetically distinct from the Mexican bird from which it arose, according to whole genome sequencing of 32 individuals, carried out in 2012 as part of a collaborative genetic analysis done in the U.S. and the Netherlands.

As happens, that intense selection for "desirable" traits has left the turkey with very little genetic diversity. How little? Less than the diversity of domestic pigs and cows, for instance.

"Commercial breeding with small effective population sizes and epistasis can result in loss of genetic diversity, which in turn can lead to reduced individual fitness and reduced response to selection," summed up the research team headed by Muhammad Aslam of Wageningen University, the Netherlands.

Which means: Limited genetic diversity can doom a species. The wider the range of genes in the species' pool, according to the theory, the more likely the species as a whole is to survive exogenous shocks, such as changes in environmental conditions that might kill off most of the flock – but a select few with appropriate traits might survive.

This is a picture of a wild turkey, which could, at a long distance, if one is not armed with spectacles or binoculars, be mistaken for a guineafowl. Credit: Wikimedia Commons

For example: Say some turkeys can store fat more efficiently than others on the same food. Leaving aside how tasty they would be, they might also be better equipped to withstand cold snaps that kill off their brothers. Wider genetic diversity is also considered an advantage in fighting off disease and so on. But when people pick and choose which animals to breed, thinking they're improving the stock – they may indeed enhance a characteristic they like, but they're going to pay a price in genetic diversity.

A classic example of a delicious world crop vulnerable to extinction thanks to over-cultivation constraining its gene pool is the Cavendish banana.

A 3,000-year-old tradition

We are talking about modern turkey farming, by the way. "Pre-contact" native Americans didn't trudge to ancient Mexico to get their turkey fix, according to a 2009 study. Genetic analysis of bird bones and coprolites (fossil feces) spanning some 2,000 years, dating from 200 B.C.E. to 800 C.E., shows the locals in the southwestern United States ate heavily of the bird, but had domesticated a turkey breed that was not the Mexican variant.

Today's American cultivated turkeys do all descend from the Mexican Meleagris gallopavo gallopavo, the genetic study proved. These turkeys began to be domesticated in about 800 B.C.E., according to an analysis of ancient mitochondrial DNA that was published in the PNAS journal in 2010. This apparently happened in Mesoamerica, where farming is believed to have begun around 9,000 years ago.

Today, America cultivates eight subspecies of toothsome turkeys, distinguishable chiefly by their plumage. Five of the varieties were formally registered in the American Poultry Association's Standard of Perfection in 1874, including the big-breasted Bronze, which is a cross with English turkeys. (Said "English turkey" is of course not native to England any more than the French are. The turkey was discovered by the Old World during the Spanish conquest.)

The Royal Palm Turkey which, like all other American farm turkeys, arose from a Mexican strain.Credit: Wikimedia Commons

The most recent subspecies to be registered, in 1971, was the Royal Palm, which sounds like it should be a tree, but is a gorgeous black and white turkey.

Why Israelis eat more turkey than other peoples

Israelis eat the same or more amount of turkey per capita than Americans or Europeans, and that's without celebrating Thanksgiving.

Consumption in Israel runs between seven and eight kilograms per capita a year, says Doron Ben-Artzi, head of the turkey section at the Israeli Association of Poultry Farmers. The Agriculture Ministry says it's rather more - eight to nine kilograms a year. Israelis used to eat even more, the ministry added, but started to shift to chicken - of which they now consume about 42-44 kilograms per capita a year.

In the U.S., the figure for 2013 was 7.4 kilograms of turkey per capita – and the Americans eat far more turkey than most other people (though Austrians have long evinced a weakness for the bird). Not so the English, where per-capita consumption of turkey is half the figure for Israel.

Why do Israelis eat so much turkey? "It's because we don't eat pigs," suggests Ben-Artzi. "Neither Jews nor Muslims touch pork. We make our sausages and smoked deli meats from turkey and beef."

Only two subspecies are cultivated in Israel: A turkey coop at Kibbutz Megadim.Credit: Eyal Toueg

Nor does Israel monkey with selective breeding of turkeys. Ben-Artzi says that Israel buys breeding stock birds from Canada and England. Of all places.

The local breeds are known as "Big7" and "Hybrid", the Agriculture Ministry relates, adding, "It is not known how they first got to Israel."

It bears noting that like with certain species of dogs, some species of turkey have been cultivated to the point that they cannot breed naturally any more, or ought not to, unless one is into turkey snuff.

For instance, the Bronze was selected and selected for size, creating the strain called "Broad-Breasted Bronze," which can only be bred through artificial insemination, because the turkey tom is likely to squash his mate to death. There are also issues with the oversized females that survive this process crushing their eggs. Happily, the so-called "Standard Bronze" can still have sex and procreate normally.



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