April, 2020 - By Koaw

Northern Virginia - (The text below is derivative of Koaw Nature’s video on YouTube.)

Polymorphism is a phenomenon in our natural world that I just love! It’s an evolutionary strategy that has proven to work for many species, including the red-backed salamander.

Polymorphism is the occurrence of two or more different phenotypes, sometimes referred to as different morphs or phases, in an interbreeding population. These morphs of the red-backed salamander show different colors in their skin pigmentation.

We often find the red-backed phase and the lead-backed phase, but the yellow-backed phase is a bit rarer. I was excited to find many morphs on the same day but even more excited when I found three different morphs all under the same log! Enjoy the video!

The eastern red-backed salamander is typically found with a reddish stripe along its back. It is also common to find the eastern red-backed salamander with no real visible stripe in its lead-backed morph. Technically we’d call a lead-backed morph an anerythristic specimen because it is lacking red pigmentation. We can also see the yellow-striped morph, where we’d technically call this a xanthochroistic or xanthic morph, as yellow has replaced the red pigmentation.

These stripes can actually vary greatly in color on the eastern red-backed salamander—from red to orange to yellow and even to white—but I’m yet to find a white-striped specimen.

Keep in mind that these morphs are not resulting from recent mutations in the DNA, rather these colors are resulting from heritable alleles, or variant genes, that exist and have existed within these populations for a long time. In most places of the northeastern North America, where this salamander is found, the red-striped phenotype is represented more than the other phenotypes in most populations, probably because of a dominant allele or multiple alleles. But in some localized populations, the lead-backed phase is more often seen.

And on occasion you can find a red-backed salamander that is entirely red, or what we would call erythristic. But I have a feeling this wouldn’t count as a polymorphism like the colors of the red-backed morph or the lead-backed morph because an all red salamander is probably all red because of a new mutation, a heritable frequency too low to count as a polymorphism.

Polymorphic traits are sustained in a population because they are favorable for adaptive evolution that allows the genes to be passed on in varying environmental conditions. Having different morphs has been a successful evolutionary strategy for this species.

-K

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