Creature Feature: Amazon molly

Where does the Amazon molly get her name? If your first guess was that she hails from the rainforests of South America, I’m sorry to say that you’d be wrong! Mollies are a group of small fish belonging to the genus Poecilia. While there are some mollies native to South America, the Amazon molly, Poecilia formosa, is actually a freshwater fish that is native to the streams of northeastern Mexico and southeastern Texas [1, 2]. 

An “Amazon Prime” molly. Drawing by Kirsten Sheehy

If she isn’t from the Amazon River, perhaps she’s just Jeff Bezos’ most recent attempt to corner the aquarium market? Sadly, the Amazon molly would probably not catch your eye while online shopping. Compared to mollies like the green sailfin molly, with his flowing checkered dorsal fin, or the black mottled hi-fin lyretail molly (what a mouthful!), with his beautiful speckles and stylish tail, the Amazon molly is actually quite drab. She sticks to a simple (though subtly glamorous) silver.

Mollies can take many beautiful forms. [Source]

So if she isn’t from the famous river and she isn’t the latest internet shopping craze, why is she called the Amazon molly? To answer that question, we must turn to classical Greek mythology. If you aren’t familiar with the Iliad by Homer, it is a story about the battle of Troy. In this battle, Achilles (of weak-heel fame) fights many foes, not the least of which is the tribe of Amazon warrior women. These fearsome warriors have inspired many stories over the centuries, including the 2017 re-boot of Wonder Woman [3].

While the Amazon molly is fierce in her own right, she is not named for her fighting abilities or super strength. To understand how she got her name, we need to look a little closer at her biology. The Amazon molly reproduces by gynogenesis. Gynogenesis is a type of asexual reproduction that requires the presence of sperm, but does not incorporate any of the male DNA into the new embryo. There are several animals that use gynogenesis, including whiptail lizards, root knot nematodes, and Ambystoma salamanders. For the Amazon molly, this means that she will mate with a male from a closely related species, but, after mating, she then ignores all of the male’s genetic material [4]. After rejecting the male’s genetic material, only her genes are passed onto the offspring, meaning she is essentially cloning herself! The 40 or so offspring that she produces are genetically identical to each other and all female.

An Amazon molly in some greenery. Drawing by Kirsten Sheehy

So, there we have it. The Amazon mollies are so named because they are all female, just like the Amazon warriors of legend. And while the Amazon molly is not from a rainforest, is not an online shopping sensation, and does not have super-fish strength, she has definitely earned a spot in biological legend for her super-cool reproductive strategy. For the Amazon molly, the past, present, and future truly is female.

Kirsten Sheehy is a PhD student in the Laskowski Lab at UC Davis. She is excited to be using the Amazon molly as a model organism to explore behavioral plasticity.


References:

[1] Balsano, J.S., Rasch, E.M., Monaco, P.J. (1989). The evolutionary ecology of Poecilia formosa and its triploid associate. In: Meffe, G.K., Snelson, F.F. (Eds.), Ecology and Evolution of Livebearing Fishes (Poeciliidae). Prentice Hall, New Jersey, pp. 277–298.

[2] Heubel, K. U. (2004) Population ecology and sexual preferences in the mating complex of the unisexual Amazon molly Poecilia formosa. PhD thesis, University of Hamburg, Hamburg.

[3] https://www.imdb.com/title/tt0451279/

[4] Schlupp, I. (2009). Chapter 5: Behavior of Fishes in the Sexual/Unisexual Mating System of the Amazon Molly (Poecilia formosa). Advanced Study of Behavior. 39, 153–183.

Main Image: A grecian urn depicting a battle-ready Amazon molly. Drawing by Kirsten Sheehy

Edited by Meredith Lutz

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