Salt Glands in Iguanas; Video footage of a South American iguana swimming along a reef

The metaphorical ink had hardly dried on my post (22 March 2019) about salt glands in Galapagos Marine and Land Iguanas and their hybrids when my attention was drawn to a recent video of a common South and Central American iguana, the Green or Linnean Iguana (I. iguana), swimming along a reef off Curaçao.

It's not everyday you spot a land iguana roaming the reef in Curaçao 🦎. 🎥 : IG user turtleandray_photography pic.twitter.com/RzoNE5fZJ3

— PADI (@PADI) 1 April 2019

The question raised, of course, is: was it was feeding on the reef. I am sure that iguanas could swim for hours in sea water without taking in any sodium chloride but eating is a different matter since, like the Galapagos Marine Iguana it is difficult to see how ingestion of sea water could be avoided.

Fundamental questions about the salt gland of a number of iguanid lizards, which appear to be able to swap between a high sodium to a high potassium secretion according to diet or salinity of water ingested, remain unanswered. Some of the questions may be basic, for example, do high sodium and high potassium secretions come from the same gland in the head, or the same cells of one gland? We need some proper physiology and cell biology to find out. And more observations from divers of the type shown in the video.

For more information on the sighting of iguanas in the sea, see Greg Mayer’s post on Jerry Coyne’s WEIT here.

Salt Glands in Iguana iguana. Somebody got there first

After Knut Schmidt-Nielsen described his discovery of salt glands in marine birds in 1957, other scientists and naturalists realised that they had seen the phenomenon earlier but had no appreciated what they were seeing. In the early 1960s, salt glands were discovered in terrestrial lizards (the salt gland in the Galapagos Marine Iguana was described by Schmidt-Nielsen and his friend Ragnar Fänge in 1958).

In 1963 Knut, with Arieh Borut, Ping Lee and Eugene Crawford in a paper in Science (142, 1300) reported:

A specimen of the tropical lizard Iguana iguana which was kept in the laboratory was occasionally found with white incrustations around the nostrils. The material was water soluble and preliminary analysis showed large amounts of potassium as well as sodium. Closer observation of the lizard while kept in a glass-walled terrarium revealed that the animal had the habit of pushing its nose against the wall thereby leaving a salt deposit on the glass.

A few weeks ago I was looking for information on Mrs Kathleen Pickard Smith for my other blog on the history of keeping reptiles and amphibians. She wrote a popular book on her experiences during the 1950s, Living with Reptiles, which was published by Thomas Nelson & Sons of Edinburgh in 1961. I read the book in 1962 and eventually gave it to the Zoo library. On reading bits again while I was scanning it,  I find she noted the following about her iguana, 'Ig':

Never a fast or a hunger strike to alarm us—true, he sneezes quite a bit in cooler weather, which leaves a chalky deposit on his nostrils and on the glass of his cage, but this is quite natural.

So, again we have an observation of salt glands in action, this time in a terrestrial lizard, before the observer could appreciate what had been observed.

#180977731 / gettyimages.com