Tourists Feeding Iguanas in Bahamas Are Giving Them Diabetes

The rock iguanas of Exuma are experiencing sugar highs after being treated to alien fruit. Prolonged high blood sugar is no better for them than it is for you

Ruth Schuster
Ruth Schuster
Exquisite, endangered and exposed to diabetes: Northern rock iguanas of Exuma Island
Exquisite, endangered and exposed to diabetes: Northern rock iguana of Exuma IslandCredit: Erin Lewis
Ruth Schuster
Ruth Schuster

“Ecotourists,” a misnomer if there ever was one, probably just want to pamper the exotic iguanas of the Bahamas. Supposedly, they are there to appreciate the natural environment without harming it.

First of all, traveling for nonessential purposes is not ecological. Secondly, tourists lavishing grapes on wild lizards could end up giving them diabetes, researchers warned in a new paper published Thursday. The sugar-high treat is giving the iguanas of the Bahamas’ Exuma islands unnatural sugar highs and is damaging their glucose metabolism, they demonstrate.

How does one feed grapes to Northern Bahamian rock iguanas? On wooden skewers, as it turns out.

Why is this happening? Some people enjoy feeding animals. But it’s rarely appropriate food: bread is not good for ducks, and Bamba peanut puffs are not an ideal snack for the giant turtles in Israel’s Alexander River.

A wild Northern Bahamian rock iguana. Feeding him grapes may seem like a grand idea. Don't do it.Credit: Jimmy Baikovicius/Wikimedia Commons

It turns out that feeding grapes to the rock iguana population has become a major tourist attraction.

But tourism has moved faster than evolution. The iguanas have not had a chance to adapt to their unnatural diets and, Susannah French of Utah State University and colleagues report in the Journal of Experimental Biology – this is causing the reptiles to experience high blood sugar and possibly pre-diabetic phenomena.

One may wonder what all the fuss is about. The Northern Bahamian rock iguana (Iguana cychlura) is vegetarian. The kids eat plants and insects and the adults eat whatever fruit and leaves they can get, though it’s been recently speculated that they’re no purists. A 2016 study of Bahamian rock iguana consumption habits published in Herpetological Conservation and Biology, based on an analysis of their feces, concluded that their diet is “diverse.” It differs in dry and wet seasons, and unexpectedly – the lizards are apparently not 100% herbivorous.

One bizarre aspect is that the natural dietary habits of the wild rock iguana are poorly understood in part because of tourists. In any case, grapes are a high-sugar fruit and are not endemic to the iguanas' domain.

Nobody knows what Northern rock iguanas really eat but it isn't grapesCredit: Erin Lewis

Why are tourists feeding skewered fruit to iguanas? Because. Why do you throw bread at ducks and pigeons? Why do visitors to Israel’s safari park insist on ignoring the signs warning them not to feed the animals? Because it makes the animals happy which makes us happy. Among the mammalian set, only cats lack the ability to taste and enjoy sugar.

But sugar and processed industrial foods are no better for the other animals than they are for us. This apparently also holds true for supplying grapes to iguanas.

The dietary aberrance was postulated to have adverse physiological effects on the unfortunate animals and now the new paper shows that it does.

The fact that humans can tolerate a highly varied diet (we are technically omnivores) is the result of millions of years of evolution. But suddenly people are feeding junk and inappropriate not-junk to wild animals that haven’t had millions of years to adapt to it, rather mere decades since mass tourism began.

Northern rock iguana in Exuma. Not to be fed with exotic fruitCredit: Erin Lewis

To test their theory that grapes are bad for the lizards, the scientists tested how a controlled, unnaturally high glucose diet affects glucose tolerance (which can signal glucose dysregulation) in captive green iguanas. They performed similar glucose tolerance tests on wild Northern Bahamian rock iguanas, some that were frequently treated to grapes by tourists and others that got no grapes. The researchers evaluated short and longer-term blood glucose responses, and corticosterone concentrations in the blood.

The discovery: Experimentally sugar-charging iguanas in the lab, and tourist feeding in the wild, significantly affected the reptiles’ glucose metabolism. This is bad. Lizards loaded with sugar experienced acute increases in blood glucose following a glucose challenge; and relative to the un-graped iguanas, had significantly lower baseline corticosterone concentrations.

Among humans, it is now dogma that routinely eating a high sugar diet can ruin (“exhaust”) our ability to regulate our blood glucose. This only gets worse when we eat tons of sugar alongside tons of fat. This has never been demonstrated in rock iguanas before, but some work has been done in snakes and alligators (their metabolisms, it must be said, are not like ours).

Conclusion: The grapes alter the lizards’ glucose metabolism and that could give them diabetes, just like it does in humans. Long-term glucose dysregulation can kill.

The northern Bahamian rock iguana is extremely endangered, thanks to habitat encroachment, the introduction of pigs, dogs and more to the islands – and because of us. Some people still hunt them down and eat them. The iguanas don’t need added metabolic stress.

What can be done? Stop feeding grapes to iguanas in the Bahamas.

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