6 Animals That Are Rapidly Evolving

istock
istock

We sometimes think of evolution as a thing of the past, but it continues today, especially as environmental pressures force humans and animals to adapt to survive. Here, a few examples of animals evolving in real-time.

1. The lizard with extra sticky feet

The native green lizards that occupy the lower branches and trunks of Florida’s trees got a rude awakening when their invasive cousins, the brown lizards, moved in. Faced with limited resources and double the competition, the green lizards made a move: they abandoned the lower branches for the treetops. Up there, the limbs are thinner and smoother, so the green lizards’ bodies had to adapt to the environmental shift. To better cling to the smooth branches, their toepads grew bigger and their scales got stickier—in just 15 years and about 20 generations. “The degree and quickness with which they evolved was surprising," said Yoel Stuart, a postdoctoral researcher in the College of Natural Sciences at The University of Texas at Austin and lead author of the study. "If human height were evolving as fast as these lizards' toes, the height of an average American man would increase from about 5 foot 9 inches today to about 6 foot 4 inches within 20 generations." 

2. The shrimp that lost its eyes

In the process of evolutionary change, you either use it or you lose it—and this is certainly true for a group of cave-dwelling crustaceans. These crabs and shrimp live underground where there is no light, and the sense of sight doesn’t do much good. As a result, they’ve gone blind, relying on smell and touch to navigate the cavernous depths. When researchers compared the brains of these spelunkers to their land-dwelling relatives, they found that not only are these creatures sightless, they’re actually losing the parts of their brains associated with vision. Meanwhile, the areas that control touch and smell are getting bigger. "It's a nice example of life conditions changing the neuroanatomy," the study’s lead author, Dr. Martin Stegner, from the University of Rostock in Germany, told the BBC. It’s taken about 200 million years for the brain changes to occur, which may not seem “rapid,” but as the Washington Post’s Rachel Feltman says, it’s “a relatively short time, in the evolutionary scheme of things.”

3. The owls that are changing color

Climate change is forcing many animals to adapt to survive. The tawny owl in Finland is a good example. These creatures come in two colors, brown or pale grey. The cold white winters have traditionally favored the grey owls, which can hide from predators by blending into a snowy color scheme. But as the winters have become more mild over the last 50 years, researchers noticed a shift: grey owls are on the decline and the brown birds are thriving, better suited to blending into the bare brown branches of the forest. As more brown owls survive, more brown genes get passed down through generations. Until now, the researchers say, “an evolutionary response to a quantified selection pressure driven by climate change has not been empirically demonstrated in a wild population.”

4. The fish that’s migrating earlier

Climate change is also the driving force behind a recent behavioral shift in pink salmon. As water temperatures rise, the fish are migrating from the ocean to the river to spawn about two weeks earlier than they did 40 years ago. And this isn’t just a new behavior—it’s actually a change at the genetic level. Between the 1980s and 2011, the number of late-migrating salmon declined by 20 percent, according to Ryan Kovach, a population ecologist at the University of Alaska in Fairbanks. The change happened over just one or two generations, which suggests organisms can adapt to climate change very quickly. “We show that there has been a genetic shift towards earlier migration timing through what appears to be natural selection against the late-migrating individuals in the population,” Kovach says

5. The bedbugs with super-strength

Unfortunately, our long-running battle with these bed-hopping pests has backfired, producing bedbugs with thicker shells and nerve cells of steel to resist the harsh chemicals we lob at them. Bedbugs in New York City are now 250 times more resistant to pesticides than the bedbugs in Florida, according to researchers at the University of Massachusetts in Amherst. "Insect resistance is nothing more than sped-up evolution," says insect toxicologist John Clark. 

6. The mouse that’s immune to poison

Bad news for anyone with a fear of mice: researchers have discovered a house mouse with an immunity to Warfarin, a type of poison typically deployed to fight infestations. The super mice were discovered in Germany, where the lowly house mouse bred with its poison-resistant distant cousin the Algerian mouse. The result? A hybrid mouse with a very useful genetic mutation that gives it a leg up over its rodent relatives. Usually hybrid animals can’t reproduce, but "sometimes there is the occasional odd hybrid that has just about the right novel combination of genomes from two species that renders them, at least temporarily, superior over the pure species," says the study’s lead author Michael Kohn. “We’ve caught evolution in the act.” 

All images courtesy of iStock unless otherwise noted.

Want to Give a Retired Police or Military Dog a Forever Home? Mission K9 Rescue Can Help

Mission K9 Rescue
Mission K9 Rescue

Over the course of their careers, working dogs perform lifesaving duties while assisting members of the police force and military. These dogs receive a lot of appreciation while they're on the job, but as they enter retirement, they're often forgotten in animal shelters. An organization called Mission K9 Rescue is dedicated to placing these dogs in loving forever homes after they've served the United States.

"Our mission is to give K9 veterans—and other working dogs who have served our country—safe, peaceful, and loving homes upon retirement from service," K9 co-founder and president Kristen Maurer tells Mental Floss. "There are so many animal-loving patriots in America, and most don't realize that many of these brave, selfless dogs often remain overseas much longer than needed when they are no longer able to work. Some do not receive adequate care. We bring awareness of their plight to the public, and we work tirelessly to rescue, reunite, re-home, rehabilitate, and repair these dogs so they can live out the rest of their days in a safe and comfortable environment."

Many retired dogs are abandoned in kennels—both in the U.S. and abroad—but for some, the situation is even more severe. According to Mission K9 Rescue, working dogs are sometimes euthanized en masse when they can no longer do their jobs. The organization aims not only to remove these dogs from harm's way, but to find them forever families that are a perfect fit for them.

After rescuing dogs from both the U.S. and overseas, Mission K9 Rescue matches them with new owners. If the dog has a past handler who is interested in adopting them permanently, reuniting the pair is a priority. For all other cases, the organization goes through a rigorous process to find dogs a brand-new home.

Mission K9 also specializes in rehabilitating dogs who have suffered either mental trauma or physical injuries in their work. Just like humans, canines can develop PTSD from working in stressful, high-pressure situations. After they're rescued, animals are given as much time as they need to decompress and reintegrate into society before they're adopted. On top of the mental demands, being a working dog causes physical strain, and Mission K9 provides medical care to dogs with injuries and other issues.

Anyone can apply to adopt a retired working dog from Mission K9 Rescue. If you're interested in bringing one into your home, you can fill out the application on the group's website.

German shepherd in a bed at home.
Mission K9 Rescue

Two dogs in the backseat of a car.
Mission K9 Rescue

Dog and owner in front of home.
Mission K9 Rescue

Some Fish Eggs Can Hatch After Being Pooped Out by Swans

iStock/olaser
iStock/olaser

A question that’s often baffled scientists is how certain species of fish can sometimes appear—and even proliferate—in isolated bodies of water not previously known to harbor them. A new study has demonstrated that the most unlikely explanation might actually be correct: It’s possible they fell from the sky.

Specifically, from the rear end of a swan.

A study in the journal Ecology by researchers at the Unisinos University in Brazil found that killifish eggs can, in rare cases, survive being swallowed by swans, enduring a journey through their digestive tracts before being excreted out. This kind of fecal public transportation system explains how killifish can pop up in ponds, flood waters, and other water bodies that would seem an unlikely place for species to suddenly appear.

After discovering that some plants could survive being ingested and then flourish in swan poop, researchers took notice of a killifish egg present in a frozen fecal sample. They set about mixing two species of killifish eggs into the food supply of coscoroba swans living in a zoo. After waiting a day, they collected the poop and dug in looking for the eggs.

Of the 650 eggs they estimated to have been ingested by the swans, about five were left intact. Of those, three continued to develop. Two died of a fungal infection, but one survived, enduring 30 hours in the gut and hatching 49 days after being excreted.

Because killifish eggs have a thick outer membrane, or chorion, they stand a chance of coming through the digestive tract of an animal intact. Not all of what a swan ingests will be absorbed; their stomachs are built to extract nutrients quickly and get rid of the whatever's left so the birds can eat again. In rare cases, that can mean an egg that can go on to prosper.

Not all fish eggs are so durable, and not all fish are quite like the killifish. Dubbed the "most extreme" fish on Earth by the BBC, killifish have adapted to popping up in strange environments where water may eventually dry up. They typically live for a year and deposit eggs that can survive in soil, delaying their development until conditions—say, not being inside a swan—are optimal. One species, the mangrove killifish, can even breathe through its skin. When water recedes, they can survive on land for over two months, waddling on their bellies or using their tails to "jump" and eat insects. A fish that can survive on dry land probably doesn't sweat having to live in poop.

The researchers plan to study carp eggs next to see if they, too, can go through a lot of crap to get to where they’re going.

[h/t The New York Times]

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