When you walk into almost any aquatic pet store it’s likely that some of the first fish to catch your eye will be male guppies.
Domestic male guppies come in all shapes and colors. Together, they make shimmering masses of blue, green, purple, red, and everything in between. Wild guppies (Poecilia reticulata), on the other hand, are much different morphologically. In the wild, male guppies are smaller, less ornate, and their color is limited almost entirely to orange.
Female Guppies Love Orange
Why the low color diversity in the wild?
Well, for one, being conspicuously colorful is a dangerous game to play in the wild. Unless you’re trying to make a statement about your unpalatability (as in the case of aposematic coloration), being brightly colored and conspicuous is often a one-way ticket to a predator’s digestive tract. Animals need to balance the costs and benefits of being conspicuous. For many animals, that balance is typically expressed in terms of mating success.
This is perhaps the primary driving force behind orange-skewed color diversity in guppies. It turns out that female guppies have a particular affinity for the color orange. By the way, it’s not just any orange, but a particular hue of orange. In response, male guppies have evolved to display that same color orange in wild populations.
The males, however, have a problem. They are incapable of biologically synthesizing the carotenoids necessary to produce that particular color orange. They, therefore, have to derive them from the environment.
Where Male Guppies Find Pigments
Carotenoids are a group of organic pigments that are abundantly expressed in plants and appear to have evolved as a response to the interactions of lifeforms with light. They fill key roles in photosynthesis and photoprotection and are often responsible for the red, yellow, and orange colors of various fruits and vegetables that we are all familiar with.
Unfortunately for guppies, almost all animal life is incapable of synthesizing carotenoids. Their only way of obtaining them is to find foods rich in carotenoids. In the case of guppies, most of their carotenoid pigment intake comes from benthic algae. The male guppies eat the algae and their bodies subsequently utilize those foreign pigments to produce the color that female guppies find so appealing.
But wait…that’s not the end of the story – that would be too easy. Just consuming carotenoids and turning orange isn’t good enough. Female guppies exert a little more pressure on their prospective mates.
If a male is too orange, it isn’t appealing. The same goes for males that aren’t orange enough. To get just the right amount and hue of orange, male guppies balance their levels of carotenoids with levels of drosopterin pigments produced by their bodies.
The combined effect is a sort of yellow-orange color within the range that females seem to find most attractive. Only the guppies that can create that right balance of diet and drosopterins occupy the niche of highest attractiveness.
Why is Orange So Attractive to Guppies?
Now, all that information begs the question of where this inordinate preference for orange came from in the first place?
One of the prevailing theories is that it originated from guppy foraging behavior. In the South American and Caribbean habitats where guppies originated, nutritious orange fruit will occasionally fall into the water.
Observational studies have shown that guppies avidly consume these fruits when available and have developed a sensory preference for orange things in general. This sensory preference for the color orange eventually made its way into the reproductive strategies of male guppies looking to court females.
I’d be curious to see what would happen over time if a population developed a preference for a different color food. In the meantime, this provides us with a great example of how seemingly disjoint evolutionary occurrences, like the color of fruit and guppy mate selection, can be intimately connected.
This post was updated from an original version published in 2014
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