Lookalike Species

Lookalike Species Lumbriculus variegatus. This specimen has two tails, possibly due to injury.
Photo Credit: Dvortygirl [CC-BY-SA-3.0 or GFDL], via Wikimedia Commons

Some animals that look exactly alike may be genetically separate species.


Lookalike species. I'm Bob Hirshon and this is Science Update.

Some animals that look exactly alike may actually belong to different species. This according to zoologist Christer Erséus of the University of Gothenburg in Sweden. He and his colleagues have genetically analyzed various worms, comparing identical-looking specimens from different parts of the world.

And particularly when worms are common, when they are said to be found everywhere, the general pattern is that there are more than one under a single name.

For example, they found that one species of freshwater worm was actually two species—twice as different genetically from each other as humans are from chimps. Because these same worms are often used in scientific research, Erséus says lumping them into one species may compromise the results. I'm Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

The term "species" generally describes a group of genetically related organisms that can interbreed with one another, but not with organisms outside the group. Sometimes, species correspond with common names for and categorizations of animals: for example, lions, horses, and humans each represent separate and entire species. In other cases, though, non-scientists lump many species together into one category: for example, there are over 365 species of squirrel. That's because in everyday life, we generally classify animals according to how they look.

Granted, animals within one species may look very different from one another: all the different breeds of dogs, from Chihuahuas to German shepherds, belong to one species, Canis lupus familiaris. But generally speaking, scientists have assumed that two anatomically identical animals must belong to the same species. That's what they thought about the freshwater worms Erséus' team studied, which were classified as the species Lumbriculus variegates.

These worms are found throughout the world, and Erséus' team looked at populations from North America and Europe. Although the worms look exactly alike, the researchers analyzed them genetically and found that they fell into two very distinct groups. By one commonly accepted measure, their genetic codes were 17 percent different from one another. By the same standard, humans and chimpanzees differ by only 9 percent, and individual people differ from one another by less than 1 percent. Erséus says this suggests the two groups of worms have been evolving separately, with no cross-breeding, for millions of years.

So does that make them separate species? Certainly, on the genetic level, they're far more separate than many other officially different species. But since there's no hard and fast rule about what defines a species genetically, this may be a question that scientists grapple with for some time. Erséus says he's already identified other separate species currently classified under one name. If scientists agree, then we may discover that there are thousands of new species hiding in plain sight.

Now try and answer these questions:

  1. What is a species?
  2. Why were these worms classified as one species?
  3. Why does Erséus say they represent two different species?
  4. What do you think might be the most reliable way to define species? Genetics? Ability to interbreed? Physical appearance? Give reasons for your answer.

You may want to check out the June 5, 2009 Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: frogs fight disease, species confusion, super spider silk, tenacious mosquitoes, better cows, and more.

Going Further

For Educators

In the National Geographic News article Handheld DNA Scanners to Identify Species Instantly? read about the Consortium for the Barcode of Life. The group hopes to develop a handheld scanner, which would be available to the general public, capable of instantly identifying plant and animal species by their DNA "bar codes."

The article Lumbriculus variegatus: A Biology Profile, provides background information about the taxonomy, lifestyle, reproduction, muscle, circulation, and behavior of this species of freshwater worm (before Erséus' findings).

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