Don’t worry, we’re not going to dive into nuclear and particle physics this week. Instead, we’re dipping a toe into taxonomy — a field that makes much less sense. Really, it’s the theory of relatedness.
About 20 years ago, I set up a large display terrarium that housed several rat snakes. I wanted to show off several animals, all of which were different subspecies of the common rat snake (scientifically, Elaphe obsoleta).
The animals I had together were a yellow rat snake (E. o. quadrivittata), and Everglades rat snake (E. o. rossalleni), a black rat snake (E. o. obsoleta), a gray rat snake (E. o. spiloides) and a Texas rat snake (E. o. lindheimeri). The display was fascinating, because all the snakes were so similar yet so different.
If I had that same display today, with the exact same animals, I would no longer have examples of five different subspecies. Instead, I would have two separate species (Pantherophis spiloides and P. obsoletus). The Everglades, Texas, black and yellow rats are considered to be simply color phases of P. obsoletus, now called the eastern rat snake.
Those of us who keep reptiles and fish constantly have this problem. You get to know an animal under one name, and then the taxonomists yank the rug out and suddenly that’s not the name anymore. Animals get reclassified, species get lumped together or split apart, color forms become new species, and so on. It’s frustrating and annoying.
But, on the other hand, taxonomy — the science of describing, classifying and identifying plants and animals — has come a long way in a very short time. Blame it on the DNA.
You might remember a little taxonomy from high school. “King Phillip came over for good soup” is a mnemonic used to help remember the levels of taxonomic classification: Kingdom, phylum, class, order, family, genus and species. Each level narrows in scope until we come to organisms that are similar enough to breed and produce fertile offspring.
As an example, let’s look at us. Most people know humans are classified as Homo sapiens. However, our full classification is kingdom Animalia (all animals), phylum Chordata (animals with backbones), class Mammalia (mammals), order Primates (lemurs, pottos and monkeys), family Hominidae (apes), genus Homo (humans), species sapiens (modern man). It’s not a perfect system, but it’s serviceable.
Once upon a time, taxonomists had to rely on appearance and behavior to determine how to classify a new species. This system of educated guessing resulted in lots of missteps. The bonefish is a good example. When it was originally described in 1758 by Carolus Linnaeus (the man who invented this classification system), he called it Esox vulpes.
Esox is the genus that contains freshwater pikes, pickerels and the muskellunge. Clearly, a bonefish is not a pike. But look at it: A long fusiform shape, no spiny fins, a deeply forked tail. If it weren’t for the toothless mouth, they’d be pretty similar. And it was the closest match he could find.
Later scientists realized his mistake, but again they had no good match. For a while they put it in Clupea, the genus Linnaeus set up for herrings. When they realized that was also a poor fit, they gave it its own genus, Albula, and there it’s been for more than 170 years.
Much of the recent disruption has been caused by genetic studies, which can do much to reveal the true nature of how closely related animals really are. Bonefish taxonomy didn’t change at all from 1850 until about 20 years ago, when researchers looking at DNA realized the two named bonefish species were actually several species — maybe a dozen or more.
Studies continue, but the work is slow (mostly because there’s no money in it). Since the newly discovered species are impossible to tell apart by eye, most people don’t give two hoots anyway.
Another problem with using visual cues to determine relationships is that sometimes animals which look alike aren’t closely related. For example, a mangrove snapper and a Mayan cichlid look quite similar, but cichlids are actually far more closely related to damselfish — little coral reef species common in saltwater aquariums.
It’s called convergent evolution: Unrelated animals responding to similar pressures and coming up with the same adaptations. We see it all over the world. Green tree pythons and emerald tree boas look nearly identical, despite being unrelated and living half a world apart. Wolves and the now-extinct thylacine (Tasmanian tiger). Bats and pterodactyls.
DNA analysis is changing the classification of birds in ways never before imagined. For example, grebes — once thought to be related to loons based on physical similarity — are now known to be more closely allied with flamingos and doves. Falcons have been found to be more closely related to parrots than to hawks and eagles. Ducks are an enormous puzzle that we are just beginning to sort out.
The new tools of taxonomy will eventually lead to a better understanding of life on our planet, but there will be growing pains. What we are sure of so far is that our basic understanding of classification has been vastly oversimplified.
Right now, we can’t even properly define what a species is. One common definition is that if animals can interbreed and produce fertile offspring, they must be the same species.
The snakes that I mentioned at the beginning of this column will readily interbreed with one another. They can also breed and produce fertile offspring with king snakes, milk snakes and gopher snakes.
Yet it’s clear these animals — which live in a huge variety of habitats, look nothing alike, and have adult sizes ranging from 20 inches to 8 feet — are not the same species, nor even the same genus. Nature once again stymies our efforts to put everything into neat and tidy categories.
So when you find that an old reference book doesn’t have the same name for a species that you’re used to, don’t curse the taxonomists. They’re just trying to understand how the world works — and it turns out they’re really no better at it than the rest of us.
Capt. Josh Olive is a fifth-generation native Florida Cracker and a Florida Master Naturalist, and has been fascinated by all sorts of wild things and places since he was able to walk. If you have questions about living with wildlife, contact him at Publisher@WaterLineWeekly.com or 941-276-9657.