slc45a2

doggosrbest  asked:

Have you seen the scientific american article titled "Save the White Tiger"? It seems to me that it's a little misguided? Like "we have a responsibility to save" white tigers? They're talking about expanding the gene pool of white tigers. Is this legit conservation?

It’s not real conservation, no. It’s a bunch of talented scientists (I think it’s written by the people who isolated the gene that causes white tigers to be white) who don’t really understand the larger conversations surrounding why conservation should happen and who apparently don’t understand much about animal behavior or inbreeding depressions. There’s like two things just blatantly wrong that are scientific and then a bunch of really woogly conservation stuff. (I am kind of consistently appalled lately at the erroneous animal related things SA has been publishing, e.g., Bekoff’s commentary on Harambe). 

“Similar variations in SLC45A2 have been observed in other vertebrate species ranging from humans to chickens. With rare exceptions the swap’s only effect on the animal is a decrease of external pigmentation. That’s what makes the white tiger white. And until trophy-hunting humans came along the mutation made little difference to the animals’ ability to survive and reproduce—most of its prey species are color blind.“

This isn’t how being able to not see color works, because animals can still see contrast. A high-contrast white-and-black animal is still going to stand out starkly in a low-light jungle compared to an orange one (which would appear as a shade of grey among shades of grey to an animal without color vision). More importantly, the reason light coloration is maladaptive is because it makes animals more vulnerable to predators - and baby tigers are plenty vulnerable for all that they’ll grow up to be beasties. Mothers of many species will abandon light colored cubs for exactly that reason; because they’re so easily spotted and picked off, they’re pretty much a waste of resources to try to raise. The humans hunting for cats is a fallacious leap as to why they’re rare - in fact, the article mentions earlier how rarely the white mutation occurs in natural populations so I don’t know where that came from. 

“Almost all of the white Bengals alive today are descended from a solitary male cub that was captured in 1951. Deliberate inbreeding has maintained the animals’ recessive coloration but it also has led inevitably to a whole range of health problems that helped inspire William Conway’s “two-headed calves” overstatement. In fact, observations of 52 white tigers born in the U.S. at the Cincinnati Zoo detected no significant heritable defectsother than some weakness in the animals’ eyesight

In any case, we now know how to reduce or eliminate the problems that have arisen from inbreeding among white tigers. Now that the crucial mutation has been identified, it will be possible to identify and crossbreed pairs of Bengal tigers, each one possessing a single copy of the recessive gene. Basic Mendelian rules give a 25 percent probability that any given pregnancy will produce white-tiger offspring while significantly expanding the gene pool of healthy animals.”

Apparently these authors also have no idea how you actually get out of an inbreeding depression… so they make a claim that as long as you’re not breeding cats with the characteristics {white, inbred} to {white, inbred} cats you’re going to have healthy cubs. Um, no. And they try to use basic Mendelian genetics as proof when all punet squares really tell you is how many of what color cat you’ll get. 

If you think back to basic high school bio, Mendelian genetics tell us that if you take two animals that are heterozygous (one of each gene, one normal and one white mutation) and breed them, you’ll get a probability of the cub colors that is 1:2:1. Out of four cubs, one would be double recessive and turn out white. One would have double dominant genes and be orange with no trace of the white gene. Two cubs - the ones that matter here - would be like their parents, with one white gene and one regular. Those are the ones that the authors of this article are saying should be bred to produce ‘healthy’ white tigers… except they’re the offspring from exactly the same inbred pairings as the white cats. 

The only way to actually get out of an inbreeding depression is to add genetic material from animals unrelated to any in the current captive population: so we’d need to find either wild white tigers or wild tigers that are heterozygous for an incredibly rare genetic mutation (which happens to be invisible). Oh, and we don’t only need one - in order to really turn around the genetics of the population, you’d need a bunch of individuals. Ergo, it’s pretty much impossible to breed ‘healthy’ white tigers - and definitely not the way the authors are suggesting. 

The article also ends with an odd stance that tells you that the authors aren’t very well versed in the actual conservation debate surrounding white tigers:

“And recognizing that white tigers are part of the natural genetic diversity of their species, we humans should consider saving them. (….) No one knows how many centuries—quite possibly millennia—white tigers lived freely in their natural habitat before human hunters eradicated them. Doesn’t our species now have a responsibility to maintain at least a few white Bengals in good genetic health?”

Okay, again, they’re doing this weird thing where they blame the reason that white tigers don’t exist in the wild on human hunting. I can’t think of a single instance of a trophy hunt involving a white tiger that wasn’t modern-era canned hunting… except maybe in really old stories, and I don’t think I’ve ever seen evidence of an actual trophy. 

What the authors are basically positing is this: because they can exist, they should, and conservation efforts should facilitate that. They seem to be predicating that assumption on the idea that all genetic diversity is valuable, even if preserving some of it comes at the cost of reducing genetic diversity in the captive population (because breeding inbred animals contributes to the inbreeding depression that all endangered captive populations are carefully managed to avoid perpetuating as much as is possible). 

There’s a huge debate right now going on about what is actually valuable diversity in a species, and why/if we should conserve it - which gets down into a discussion about the philosophy of conservation. Conservation with the goal of putting healthy populations back into the wild is going to view the genetics it wants to conserve very differently than conservation from the standpoint of showing off the range of animals that existed in the wild before we killed all of them. Color morphs are pretty and yes, they’re possible, but does their existence really contribute anything to the end-goal of conservation? We don’t know. I definitely don’t agree with the guilt-trip the authors end with - because we’ve supposedly killed all of them off, it’s our responsibility to spend extra resources bringing back and conserving a genetic mutation whose presence has been artificially inflated in captive populations, popularized, and exploited for profit. 

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Since the 1800s, people have sometimes reported seeing pure white tigers, these have become known as Stripeless Tigers (or Ghost-Striped Tigers). Written descriptions can be found in many places, including the 1829 book Le Règne Animal written by French zoologist and naturalist Georges Cuvier. “A white variety of Tiger is sometimes seen, with the stripes very opaque, and not to be observed except in certain angles of light.”

However these cats are far from a mystery animal from historic documents - they are an extremely rare color morph. These tigers not only hold the genetic mutation in the pigment gene “SLC45A2″ (this mutation causes pigment changes in red and orange colors while not affecting black colors at all). They have another mutated gene on top of that one which causes them to lose the color in their stripes. 

In 2004, a stripeless white tiger was born to two normal healthy bengal tigers at a wildlife refuge in Alicante, Spain. This cub was named Artico (left photo). In 2008, another was born at Cango Wildlife Ranch, near Cape Town, South Africa. Her name is Fareeda (right photo). Fareeda is thought to be the first white tiger born in Africa, even with her lack of stripes. It is said that these tigers are two of only 20 stripeless tigers in the world, all living in captivity.