Tiger Salamander

Tiger Salamander. Image taken at the San Francisco Zoo.

Tiger salamanders are large burrowing salamanders found throughout North America. They have been the focus of a lot of research particularly because various species of tiger salamander have different possible developmental paths and how and why they take one path over another has been a fascinating area of study.

For example, some of these salamanders are neotenic. This means that when conditions on land are particularly harsh, they will retain some of their larval characteristics, like big, fluffy external gills and never complete metamorphosis into a terrestrial adult form. They will stay safely in the water for their entire lives. Although they keep larval characteristics, they can still reproduce.

And then there are several species of tiger salamander that have cannibal morph larva. That is, there are two larval forms, a smaller form that eats aquatic invertebrates, and then a much larger form that can also eat the smaller larval form.

Tiger salamander larva

A cannibal morph tiger salamander larva eating a non-cannibal morph tiger salamander larva. Image by David Pfennig and James Collins.

Scientists wanted to know what triggers a “typical” larva to morph into a cannibal larva? They discovered several environmental factors, that actually make a lot of sense. For example, cannibal morphs develop when they live in very dense populations with other tiger salamander larva. This makes perfect sense because if the population is dense, then there is a lot of competition for food and potential food if you can eat your own kind. Another factor that determines whether or not a larva develops into a typical morph or a cannibal morph is how closely related the larva around them are. If they are closely related to nearby larva, they are not likely to develop into a cannibal morph. Again, it makes sense because if they are related then they share genes and they don’t want to eat an animal that will increase the likelihood of passing those shared genes on to the next generation. Studies have also shown that when given the choice, cannibal morphs will choose to eat non-kin rather than their own kin. And yes, they can tell if they’re related and even how much they’re related to each other. Experiments indicate that it is probably by sense of smell.

Another question that had intrigued scientists is why don’t we see more cannibal species in nature? When you think about the benefits of cannibalism, such as removing competition for food and possibly mates if its sex specific cannibalism, as well as having a nearby food source, it seems like evolution would have selected for this more often. They found a good explanation for this one as well. Most diseases are pretty host specific. For example, while there are a few diseases that can be transmitted between us and say our cats, there are a number of diseases that can’t be.  Carnivores in general prey on the sick and the weak, or the easiest to catch prey. Laboratory results showed that cannibal tiger salamander larva did in fact choose to prey on the sick and were more likely to die from an acquired disease. And so cannibalistic tiger salamander species kind of have the best of both worlds. They aren’t cannibals unless the conditions are optimal for them to be so. Then some of them can switch.

And what adorable little cannibals they are!

Tiger salamander

A tiger salamander. Image taken at the San Francisco Zoo.

By the way, the California tiger salamanders are not doing so well and there has been constant fights from groups who want to develop on prime tiger salamander habitat to remove their protected status in California. The fight was won yet again this year when the California Fish and Game commission voted to keep them protected under the California Endangered Species Act. There are actually a lot of things working against these animals right now and they need the limited protection they are granted because of their status.  Stay informed and find out what you can do to help protect them at Save the Frogs, which incidentally will also save the salamanders.