Lesser siren

Very little is known about this unique amphibian, the lesser siren. Image taken at the California Academy of Sciences.

This elegant little amphibian is the lesser siren, one of only 4 species of siren, all of which are found in North America. They all have the same body shape-long and slender, like an eel. They don’t have any rear limbs. The only limbs they have are the two tiny, weak arms in front, one of which is showing above.

These animals spend a lot of their life buried in mud or sand at the bottom of swamps or ponds. They can tolerate some pretty harsh conditions.  If their pond dries out, they can cover themselves in a mucus that hardens to make a thick papery cocoon with just their mouths sticking out, where they can wait for rain to restore their habitat. In the rainy season, at night, they can even travel short distances across land.

This group of amphibians will retain their larval characteristics for their entire lives. This means they will always have those big, fluffy gills (even though they also have small lungs), no eye lids and a lateral line, which allows them to feel pressure changes, and thus objects, in the water.  There have been some cool experiments to see if they can make a siren metamorphose. It seems that they have completely lost (or never had?) this capacity genetically. When researchers injected other tailed amphibians that retain their larval characteristics, such as the axolotls, with a hormone called thyroxine, they can induce metamorphosis, but not in sirens.

Scientists have wondered why certain amphibians will stay in their larval stage or retain larval characteristics. Why would this have evolved? One thought is that the aquatic habitats are surrounded by hostile land and therefore it’s beneficial to stay in the water. Another thought is that in some areas the water doesn’t have a lot of iodine, which is necessary to produce the hormone thyroxine needed for metamorphosis.  This is still an open area in research.

By the way, if you’re wondering what a true siren call is, it’s actually a distressed yelping sound. And honestly, I can’t imagine a siren call that would work better as an irresistible lure for me than the call of an animal in need.  Well…maybe a U2 song.