What has three eyes, two noses, and an antenna poking up like a little puppet from its head?
That would be a unique specimen of the freshwater crab Amarinus lacustris, discovered in New Zealand and described in this week’s issue of the journal Arthropod Structure & Development.
The “tri-clops” crab’s peculiar extra parts, and its malformed brain, are likely the result of a combination of bodily missteps. The crustacean has characteristics of a conjoined twin (duplicated parts: in this case, eyes) and a messed-up attempt at regeneration (crabs can regenerate an eye if one is damaged, but here an antenna popped up instead). (See: “Pictures: 5 Animals That Regrow Body Parts.”)
Nature is no perfectionist; boo-boos happen. For scientists, these oddities are not just fun to study but valuable to understand.
“Naturally occurring anomalies show what is possible,” said Gerhard Scholtz, of Humboldt University in Berlin, who led the new study on the weird crab.
Studying them “is like learning from mistakes. If things go wrong, and you understand the causes and mechanisms, you understand the causes and mechanisms for normal development as well.”
We took a look at some of nature’s most fascinating blunders.
There are bad genetic mutations and fatal ones—which, by their nature, are weeded out of the gene pool. But other genetic tweaks stick around, because they offer some competitive advantage, something that improves survival. (Sound familiar? Darwin had it figured out in his “survival of the fittest” theory.)
Genes aren’t solely responsible for abnormal beasts. For instance, the development process, which involves genes but also other factors, can stumble: If a body part develops at a slightly different time than usual, there can be a cascade of effects.
The environment too may fiddle with processes. For example, the temperature of incubating reptile eggs decides the sex of the animals, and excess heat can cause two heads to grow instead of one. (See: “Two-Headed Reptile Fossil From Age of Dinosaurs Found.”)
Often, the cause of an aberrant form isn’t just one thing but a mix of factors, said University of Iowa neuroscientist Mark Blumberg, author of the book Freaks of Nature. As he explained it, “Many of the normal features that we see in animals—think elephant trunks, enlarged genitalia in female hyenas—may have arisen as evolutionary novelties with changes in the environment” that altered how the animals developed.
He added, “some scientists now believe that the genetic changes follow rather than lead the process.” So instead of one culprit, a mix of environment, genes, developmental steps, and time can together breed a whole new animal.
Mutations can also lead scientists to a helpful process of backward reasoning, Humboldt University’s Scholtz said. “One observes a pattern and tries to reconstruct the mechanisms and historical pathways that might have led to this result—like a detective using [a blood-spatter pattern] to reconstruct a murder.”
Today, of course, scientists don’t have to wait for nature to mess up. They can create their own mutants in the lab by fiddling with cells or plucking out genes.
Genetically altered knockout mice, for example, are used in many research studies.
In the 1950s, Idaho sheep ranchers were startled by the birth of cyclops lambs—animals with a single eye smack dab in the middle of their foreheads. They also had underdeveloped brains.
It turned out that flowers were to blame: A chemical in corn lilies that the animals had been eating during drought periods was stunting the lambs’ embryonic growth.
Later, scientists figured out that cyclopamine, as the chemical was named, blocks the activity of a gene vital to embryonic development. More recently, the chemical has been studied for its antitumor activity.
Though less bizarre looking than some, one of the more important “freaks” emerged in the early 1900s, before the field of molecular biology even existed: the white-eyed Drosophila fly.
By studying the fly—which appeared in a batch of normal red-eyed flies he was breeding—evolutionary biologist and embryologist Thomas Hunt Morgan helped figure out the role that chromosomes play in heredity.
Over the years we’ve covered lots of nature’s anomalies, especially the two-headed kind.
According to Scholtz, such examples of Siamese twins most likely result from the incomplete splitting of an embryo that otherwise would have become identical twins, and they occur in all major animal groups.
Nature’s bloopers can be truly useful to science. The rest of us just love sending pictures of these freakish creatures to our friends. Albino cyclops shark, anyone?
Follow Jennifer Holland on Twitter.