Exploring dimorphism

Hi everyone, this is Ash, Keeper II in Herpetology. Today I would like to talk about a pretty cool biological variation that occurs in our natural world: sexual dimorphism! What is this, you ask? It is a term when males and females of the same species appear externally different. These differences have primarily evolved through sexual selection by chosen mates and produce viable offspring.

There are many examples of this that we’re all familiar with. Some examples include (most) male lions being larger than females and having a mane; male peafowl with their extravagant tail feathers and bold colors while females are a little less adorned; and in a very extreme case, female deep sea anglerfish that can be many times the size of their tiny parasite males (if you don’t know about anglerfish, look them up…they are…WEIRD!). What do they all have in common? Sexual dimorphism! 

As a herpetologist, I am here to talk about snakes! Did you know that snakes can exhibit sexual dimorphism? They exhibit it in a number of different ways. For example: In the green anaconda, Eunectes murinus, females are heavier and longer than males. This works out well because the larger the female, the more offspring she could potentially produce. It also is an advantage for the males to be smaller. Often “breeding balls” (think “dogpile” except with snakes) will occur where many males will compete for a chance to reproduce with the same female. As the males are so much smaller, they are less likely to expend energy trying to mate with another smaller snake in the breeding ball, which would most likely be another male.

Another example: banded rock rattlesnakes, Crotalus lepidus klauberi, exhibit a difference in male vs. female coloration. Males have more of a green-blue coloration in between their black, or dark brown banding, while the females have more of a grey-purple color in between dark bandings (see photo). They live in very rocky areas with a lot of lichen, so their different colors help them camouflage with their natural surroundings. 

Another neat example: the Malagasy leaf-nosed snake, Langaha madagascarensis, is known to have a differently shaped scales, just past the nostrils, that looks like a horn. Males exhibit a long-pointed snout (imagine a narwhal, but in snake form) and are dark brown with a yellow or white stripe going along their lower sides. The females also have nose appendages, but they appear leaf-shaped. The females are also overall a uniform grayish color. If you didn’t know better, you might think they were two different species! It is not known why they evolved to have these extreme noses, although it does seem to help with camouflage!

These are just a few examples of the variety in sexual dimorphism snakes can present. Snakes are incredibly diverse in just about every way! This is one of the many reasons why I think they are some of the most fascinating creatures on the planet!

Ashley T.
Keeper II, Herpetology