# Are firefly-like vertebrates biologically plausible?

Fireflies are amazing little insects. They have the ability to produce a pulse of light without the help of a symbiotic relationship with bioluminescent bacteria.

This works via a chemical reaction which involves a light-emitting pigment called luciferin [L] and an enzyme called luciferase

$$\text{luciferin} \ + O_2 \ _\overrightarrow{\text{luciferase}} \ \text{Oxyluciferin} \ + \text{light}.$$

So is it biologically plausible for a vertebrate to have this ability?

Let's say it has a special light organ on its head and uses this ability to communicate to other members of its species (similar to a semaphore) and/or to cause a short term dazzling effect that blinds a predator for a few seconds/minutes.

It would be something like how this guy does it (he's from monster hunter world):

• this research may interest you, pnas.org/content/115/50/12728 – John May 5 at 12:43
• If you want the light to be BRIGHT, like in the picture, bioluminescence isn't the way to go. Lots of things on this website are focused on dragons and flame. Fire will be much brighter. – DWKraus May 5 at 21:17

There are fishes living in the depths of the oceans which are capable of producing bioluminescence for the sake of mating and attracting prey.

Fishes are vertebrates, and apparently have been able to evolve this feature. Maybe they use slightly different chemical paths, but the result doesn't change. They emit light.

Sure!

As fans of Finding Nemo know, the anglerfish is a vertebrate that can glow. The chart below shows other fish (vertebrates) that have evolved bioluminescence. As the source for that chart says, it's not just a fish/firefly thing:

Lots of non-fish species use bioluminescence as well — some bacteria, sponges, jellyfish, crustaceans, segmented worms, squids, sharks, and even plenty of terrestrial species like fireflies. All bioluminescence is caused by a chemical reaction. Some of these organisms produce the necessary chemicals themselves, while others, like the anglerfish, rely on the help of symbiotic bacteria.

Broadly speaking, there are two different ways of making a creature glow: either the critter produces light by itself (as your equation demonstrates) or it gets some help. The Anglerfish uses the latter approach. It's developed a symbiotic relationship with bacteria. In your world, there's no reason that a non-aquatic species couldn't develop a similar relationship with a glowing bacteria.

• what if it's a land based vertebrates, can it be plausible? – user3556983 May 5 at 5:48
• @user3556983 You could definitely write about a land-based vertebrate with bioluminescence. Just because it hasn't happened doesn't mean it's implausible for sci-fi writing. – Andrew Brēza May 5 at 13:07
• From an evolutionary standpoint, you'd expect such a creature to live in a dark environment, but to have ancestors who didn't - because a species that evolved entirely in the dark would be unlikely to develop eyes (relying on other senses to navigate), and thus would not benefit from being able to produce light, and a species that evolved entirely in well lit areas would also not benefit (as much) from this trait. – Darrel Hoffman May 5 at 13:52
• @user3556983 - Even if it's implausible for a land-based vertebrate to evolve it (I don't find it implausible; it may have even happened before in some extinct organisms for all we know! This sort of thing doesn't fossilize), you could say that in your universe, land-dwelling vertebrates evolved from bioluminescent fish instead of normal fish like in our universe. In that case, most vertebrates would have lost the feature (since I suppose it's generally less useful on land, since land generally is well-lit, per Darrel's comment). – Dark Malthorp May 5 at 14:22

A vertebrate to evolving from a firefly isn't going to happen. If it did, it'd have to be an incredibly convoluted process which involves degrading the evolution to where vertebrate can evolve from that. Theoretically not impossible, just not likely. Also something that isn't going to happen on Earth because evolution moves forward, not backwards.

It is possible for a vertebrate to have the biological process that fireflies have to produce glowing light. It's an organ which functions independently of vertebrate status, so there's nothing stopping a vertebrate from having it.

• The question did not ask about a firefly evolving into a vertebrate. – Dark Malthorp May 5 at 0:48
• May I asked why you think that evolution has a direction? – NomadMaker May 5 at 3:02
• @Halfthawed I did actually look at the edit history - Even in it's original form, it seems evident that "firefly based" meant "I was inspired by fireflies to have this idea" not "evolved from fireflies." – Dark Malthorp May 5 at 3:36
• @Halfthawed There's species of tapeworm that are descended from much more complex ancestors. Evolution often drops features and complexity that is no longer worth the cost. – prosfilaes May 5 at 5:11
• So far as evolution is concerned, "forwards" just means the next mutation: it is possible for different groups of an animal to develop completely opposite notions of "forwards", depending on their environment - that's precisely what happened with Darwin's Finches, and lead to the development of the Theory of Natural Selection. – Chronocidal May 5 at 13:37

Most land-living vertebrates have too thick skin to make this bio-luminescent light possible. The fact that of the vertebrates cited above only fish specimen have this feature supports that. Fish have thin skin as they don't have to protect against water loss at the same degree as the land-living creatures. Obviously insects with their chitin exoskeleton have the "advantage" as chitin allows for a thin but strong build.

• fish skin still needs to be waterproof, otherwise they lose water to the ocean. – John May 5 at 12:37