Male genetically modified zebrafish aren’t exactly Casanova’s.
First things first, this is not written as an argument for or against genetic modification. It’s an intense and complicated debate, and shouting or finger-pointing will get us nowhere. Anyway, that’s for another day. Now, it’s time for funky science.
One of the arguments that opponents of genetically modified organisms (or GMOs) often use is the worry about escaping renegade organisms that take over the world (well, at least a part of it). But how realistic is this concern?
Fluorescent Fish
One of the first commercially available genetically modified animals was originally developed to detect pollution by glowing when a certain toxin was present. Soon, however, the pet trade potential became obvious. Enter glow-in-the-dark fish (or GloFish®).
Thanks to the use of a jellyfish gene, the first green glowing zebrafish (Danio rero) saw the light in 1999. Since then, other colors and species have joined the ranks of radiant fish. In 2003, they officially invaded the pet trade. In 2011, glow-in-the-dark sushi was prepared by the Center for Genomic Gastronomy. Indeed, these fish were, and are, a commercial success.
Red for Passion? Not so much…
But are they evolutionarily successful as well? With the help of red GloFish®, a research team at Purdue University sought to address this question. An earlier study suggested that female zebrafish strongly preferred GloFish® males over wild ones when the two types of male were kept separate. Does this mean that, if the genetically modified fish enter a wild population, it will end up being composed exclusively out of glowing fish? Imagine that, ponds filled with glow-in-the-dark fish!
Reality, however, is more complex. In wild conditions, our red wannabe-Casanova’s not only have to seduce the females, they have to compete with the wild males for access to females as well. And that, kind readers, seems to be where the true challenge lies. When males had to compete for a female, the wild ones were more successful. They chased the red males much more than vice versa, and were more persistent when chasing females. So, while the study did not uncover any difference in health, fertility and lifespan between the two types of male, the wild ones were more aggressive. The cause of this remains unclear, but the consequence is that the wild guys had 2.5 times as many kids as their red rivals.
To see the evolutionary consequences of this, the research team complemented these behavioural studies with a long-term population experiment. Using data from 15 generations of fish across 18 populations (over 18 500 fish!) they were able to show that, at the moment, glow-in-the dark fish are no evolutionary success story. In all but one population the red males had entirely disappeared from the scene.
Life finds a way
Of course, this study concerns only one species of genetically modified organism. Other GMO’s might be more successful in evolutionary terms. The outcome of genetically modified organisms that escape or are introduced into the wild depends on a lot of factors. On top of that, gene pools are not static. As Ian Malcolm says in Jurassic Park: “Life finds a way.”
But to learn more about the possible outcomes, studies such as these are a great help. What’s more, this study not only combines short-term behavioural experiments with a long-term population study, coupling evolutionary mechanisms and outcomes, but it shows how GMO’s can be a really good study system to address questions that are of interest to pure science as well as to its applied cousin.
Anyway, the lesson here? If you’re a zebrafish and you want to be evolutionary successful, you’ll have to do more than glow in the dark.
GloFish, GMO, zebrafish, evolution, sex, fertility, wild, health, lifespan, biology
