• Emily Costello

Cannibalistic Salamanders

Small lizard-like amphibians, with slender bodies, blunt noses and bulging eyes. Their slimy, permeable skin ties them to the water and to damp, cool environments. Famously, they are known for their ability to escape the jaws of a predator by dramatically losing their tail, however, autonomy is not the only bizarre, slightly disturbing trait of these creatures. Around one third of this species can be found in North America, within mountainous habitats where pools surrounded by damp vegetation sit undisturbed. It was here that researchers stumbled upon something strange that sparked an interest within the science world and led to future key discoveries.

The creature in question is of course, the salamander.

The specific species found were Tiger salamanders. These guys have two morphs (body types). Whilst the majority spotted had the iconic blunt head and stunted teeth of a typical salamander, others had rather wide heads with odd teeth protruding – which when looked at closely, resembled fangs. Whilst both groups belonged to the same species, they had rather striking differences in appearance… but what those differences meant in terms of behaviour and diet, was even more so.

Before I get to the gruesome details, you may be wondering why there are two different body types within the same species group. If you know a little about natural selection, you may have come across the term ‘phenotypic plasticity’ before. If not, essentially some creatures can shape- shift due to pressures from their environment. This is exactly what is happening here. The tiger salamander, when still only a larva within the egg, will pick up on cues from their surroundings. These then signal to the body to become one of two morphs: A ‘typical morph’ or the rather suitably named ‘cannibalistic morph’. Yes. Cannibals.

Okay, so some salamanders eat their neighbours. Disgusting, yes, but very beneficial. The protein from another salamander will help that individual grow strong and compete against others for food and space. It makes sense. Why then are there only a percentage of the group with this thirst for blood? Well, as I mentioned earlier, the deciding factor determining the path each salamander’s life will take is due to a surrounding pressure. You may think when food is scarce, it may encourage this type of behaviour. However, even when food and water is stable enough to provide for all members of the group, cannibalistic morphs continue to appear. In this case, research may have discovered another reason for these savage individuals and more interestingly, highlights the importance in the phrase ‘family matters.’

In 1993, researchers put salamander larvae to the test – how much can they really sense from their environment? Limiting food, increasing competition and introducing a predator in their pond all effected the type of morphs that were produced, but it seemed these guys were also fully aware who they shared the brooding patch with.

When the larvae were reared in family groups, with similar genes, an average 40% developed into cannibals. Comparing that to the larvae that were reared in mixed groups of unrelated individuals, where a staggering 89% turned on each other with their newly formed fangs and taste for blood. As unbelievable as it seems, this data suggests that as well as other cues, tiger salamanders can identify relatedness between themselves and their neighbours before ever hatching. Surrounded by relatives, it seems this urge to eat each other subsides, perhaps due to the fact that these related individuals surviving to breed could benefit you by a percentage of your own genes passing onto the next generation.

The inclusive fitness theory suggests – altruism (doing something costly to benefit another) between individuals in a group enables others to pass on their genes. In the case of the tiger salamanders, taking on the form of the cannibal morph would set you up for success but also hinder others in your group. By losing the ability to grow from all the easy meals around you, you are allowing them to breed themselves. This is higher in related groups showing that family really does matter – especially if you are a little tiger salamander floating in an isolated pool at the top of a North American mountain.

This happens elsewhere in nature too. For example, worker bees taking on totally different body shapes and roles to the drones and their queen, all for the benefit of the group. By understanding why these strange and weird differences occur in one species it can help us understand another. As amphibians, salamanders fall into the category of most threatened animal group in this planet right now. Amphibian numbers are dropping at a rate higher than any other group. It is important to understand how they function and what allows them to thrive if we are to help them… and hey, now you know that some salamanders grow fangs, especially those that don’t have much family.

As always, if you want to read the research -> Pfennig, D. and Collins, J., 1993. Kinship affects morphogenesis in cannibalistic salamanders. Nature, 362(6423), pp.836-838.

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