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A Natural Gene Drive Could Steer Invasive Rodents On Islands To Extinction

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In the battle against the invasive house mouse on islands, scientists are using the rodent’s own genes against it.

With the right tweaks, introducing a few hundred genetically altered mice could drive an island’s invasive mouse population to extinction in about 25 years, researchers report in the Nov. 15 Proceedings of the National Academy of Sciences. The trick is adding the changes to a section of mouse DNA that gets inherited far more often than it should.

Scientists have been creating similar extra-inheritable genes — called gene drives — in the lab. The chunks are designed to get passed on to most or all of an animal’s offspring instead of the usual half, and make those offspring infertile in the bargain. Scientists have used gene drives to reduce populations of mosquitoes and fruit flies (SN: 12/17/18).

But mammals are a different story. Scientists have previously synthesized a gene drive that gets passed on in mice about 80 percent of the time (SN: 1/23/19). But the drive isn’t strong enough to stop a population quickly.

Luckily, nature has it handled. A haplotype is a naturally occurring group of genes that gets passed on as a unit during replication. The genome of the house mouse (Mus musculus) has a particular haplotype, called the t haplotype, that gets passed on to offspring more than 95 percent of the time, instead of the typical 50 percent.

This natural gene drive has benefits, says Anna Lindholm, a biologist at the University of Zurich who was not involved in the study. It “evolved naturally and continues to be present in the wild, and we have as yet not found resistance to it in wild populations,” she says. It’s also not found in species besides M. musculus, meaning it probably won’t spread to other noninvasive mice.

Molecular biologist Paul Thomas and his colleagues decided to target the t haplotype with the cut-and-paste molecular tool called CRISPR/Cas9 (SN: 8/24/16). They used CRISPR to insert the gene sequence for the CRISPR tool itself into the t haplotype. When a male mouse carrying the altered t haplotype mates with a female, the inserted genes for the CRISPR tool spring into action. It uses a special genetic guide to target and inactivate the gene for the hormone prolactin — rendering any baby female mice infertile.

The best part is that the natural t haplotype can also sterilize males, says Thomas, of the University of Adelaide in Australia. Males with two copies — homozygous males — won’t reproduce at all.

“If you could get a t to spread through a population, you could get homozygous males being sterile,” he says. “And with the addition of the CRISPR element on top of that, we get homozygous females that are also sterile.”

To find out how well the t haplotype mice do on an island where mice are wreaking havoc on biodiversity, the scientists used a computer simulation of an island with 200,000 mice. The team found that adding just 256 mice with the CRISPR-altered t haplotype could successfully drive the mouse population to zero in around 25 years. Even without CRISPR, adding mice with the normal t haplotype could tank the population in about 43 years.

But models aren’t mice. In a final test, Thomas and his colleagues made the model reality. The team altered the t haplotype in a small group of mice in the lab and used genetic tests to show that those mice would pass on their new genetics 95 percent of the time.

“This is a clever idea, to build on the t haplotype natural drive system and use CRISPR, not for spreading the construct, but for damaging genes necessary for female fertility,” Lindholm says. “This is a big advance in the development of new tools to control invasive mouse populations.”

The next step, Thomas says, will be to test the effects in real populations of mice in secure enclosures, to find out if the genetically tweaked t can stop mice from reproducing. The scientists also want to ensure that any engineered mice released into the wild have some safety mechanism in place, so other mice elsewhere remain unaffected.

The final version might target tiny mutations that only occur on one island where the pest population is isolated, Thomas suggests. If the mouse escaped onto the mainland, its altered genes would have no effect on the local mice. The scientists also want to consult with people living in the area, as officials did when genetically modified mosquitoes were released in Florida (SN: 5/14/21).

Finally, he notes, 25 years is a long wait for some endangered island populations. “We would love to see CRISPR work faster,” he says. “It’s still a work in progress.”

Animals

Here Are 3 People-Animal Collaborations Besides Dolphins And Brazilians

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We’ve all heard that dogs are a man’s best friend, but our canine companions don’t make up the entirety of humankind’s friend circle. Humans have cooperated with wild animals throughout our evolutionary history, forming reciprocally beneficial relationships known to biologists as mutualisms.

One particularly piscine partnership that made headlines recently can be found in Brazil, where fishers catch nets full of fish with the aid of the local bottlenosed dolphin (Tursiops truncatus gephyreus).

This team-up started over a century ago, probably when fishers first noticed that the presence of dolphins was a clue that fish were hiding in the murky water, says Mauricio Cantor, a behavioral ecologist at Oregon State University’s Marine Mammal Institute in Newport.

“The dolphins are really good at detecting fish and herding them toward the coast,” he says, “and the fishers are really good at trapping the fish with their net.” Once the fish are mostly secured in the net, the dolphins are sure to snag a few for themselves.

In a study published January 30 in the Proceedings of the National Academy of Sciences, Cantor and colleagues used long-term data to show that the dolphins and fishers respond to cues from the other, and without experienced partners who know the right dance steps, the routine falls apart. “This is a really remarkable and impressive study,” says Pat Shipman, an anthropologist at Penn State University who was not involved with the research.

This fishing partnership is an important part of the cultural identity of both the fishers and the dolphins, but Cantor and his colleagues’ work shows that the practice is in decline. And among human-animal partnerships, it’s not alone. “Most of the historical cases are declining or already gone,” Cantor says. 

Given their rarity and charm, let’s take a look at some of the other known examples of human-animal cooperation.

People used to team up with orcas to hunt whales in southeastern Australia

The bottlenosed isn’t the only dolphin that humans have formed beneficial arrangements with. In the 1800s, several hunters began working with a pod of orcas (Orcinus orca) to catch large whales. At Twofold Bay in southeastern Australia, some orcas would find and harass a whale to tire it out, while others swam to alert whaling crews (made up of Aboriginal Australians and Scottish immigrants) that they’d found prey.

Once the whalers arrived and harpooned the whale, they let the orcas eat the tongue — a delicacy in the killer whale culinary world — before taking the rest for themselves.

While the dolphins and fishers in Brazil were chasing the same prey — schools of migratory mullet (Mugil liza) — the orcas and whalers were mostly after different things. The key similarity, Cantor says, is that there’s enough prey for everyone, so that no competition arises to spoil the partnership.

This relationship ultimately ended when some settlers killed two orcas, which drove the cooperative pod away from the bay, seemingly never to hunt with humans again.

These birds guide people to honey in Africa

Sometimes, a name says it all. Such is the case for the greater honeyguide (Indicator indicator), which has been labeled in both English and Latin based on its most famous trait. These birds live in sub-Saharan Africa, and cooperate with local honey hunters to gain access to succulent beeswax (SN: 7/21/16).

Birds, like humans, don’t like to be stung by bees, so a honeyguide that’s hankering for beeswax will chirp at a person to signal that they should follow. The honeyguide then leads the hunters to a bee nest and lets them do the dirty work of harvesting it.

A greater honeyguide, a small bird with a tan body, dark brown wings and head, and a red beak, looks to the right
In search of beeswax, the greater honeyguide (Indicator indicator) helps humans in Africa locate bee nests full of honey.Michael Heyns/Wikimedia Commons (CC BY-SA 4.0)

Like with orcas, honeyguides and humans are after different parts of the prize: Humans want the honey, while the birds want the wax. Honeyguides are so helpful for finding bee nests that the Borana people of East Africa blow a special whistle called a “fuulido to summon them when it’s time for a honey hunt.

Similar to the dolphins in Brazil, the relationship with honeyguides is an important part of many African cultures. Legend even has it that a scorned honeyguide, if denied beeswax on prior hunts, will lead the hunters not to delicious honey but instead into the jaws of a dangerous predator, like a lion.

Wolves and people were once on the same side when hunting big game

To see the most extreme outcome of human-animal partnership, take a look at 39 percent of the country’s beds, couches and backyards. That’s about how many households in the United States own a dog. But it turns out a canine doesn’t have to be domesticated to get along with humans; Indigenous stories from peoples in North America describe cooperating with gray wolves (Canis lupus) to hunt big game like elk and mammoths.

The wolves would run down the prey until it tired, and humans would make the kill once they caught up. Because these prey items were so massive (like the large schools of mullet), it didn’t matter that humans and wolves were after the same thing — there was plenty to go around.

Though this furry friendship doesn’t exist anymore, wolves are still important in many Indigenous cultures. Some even still continue the practice of leaving some meat for the wolves after a hunt.

Though human-animal partnerships are rare and on the decline, they “give us an illustration of how positive our human interactions can be with nature,” Cantor says.

For Shipman, the urge to engage with other animals is a defining trait of humanity. “It’s in some ways as fundamental to humans,” she says, “as being bipedal.”

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A Newfound Silent Frog May Communicate Via Touch

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A newfound species of frog doesn’t ribbit. In fact, it doesn’t make any sound at all.

Many frogs have unusual characteristics, from turning translucent to being clumsy jumpers (SN: 12/22/22; 6/15/22). The recently discovered amphibian lacks a voice. It joins a group of seven other voiceless frog species called spiny-throated reed frogs that reside in East Africa.

Instead of croaking, the spines on male frogs’ throats might help their female counterparts recognize potential mates via touch, sort of like braille, says conservation biologist Lucinda Lawson of the University of Cincinnati.

Lawson and colleagues spotted the little frog, only about 25 millimeters long, in 2019 while surveying wildlife in Tanzania’s Ukaguru Mountains. The team immediately recognized the animal, now named Hyperolius ukaguruensis, as a spiny-throated reed frog. But something seemed off.

“It [was] the wrong color,” Lawson says. Most frogs from this group are green and silver, but this one was gold and brown. Some quick measurements to check if the peculiar frog simply had trivial color variations or if it could be a new species revealed that its eyes were smaller than other spiny-throated reed frogs. The researchers agreed: “Let’s do some genetics,” Lawson says.

They ran DNA tests on two frogs that looked like they belonged to the suspected new species, as well as 10 individuals belonging to known spiny-throated species. Comparing the golden frogs’ genetic makeup with that of the others revealed the oddballs were genetically distinct, Lawson and colleagues report February 2 in PLOS ONE.

a Hyperolius ukaguruensis stands on a leaf. It is golden-colored with darker splotches along its back
The golden-hued Hyperolius ukaguruensis stands out from its fellow spiny-throated reed frogs, which also lack a voice but are typically green.Christoph Liedtke

Each frog species in this voiceless group — including H. ukaguruensis — lives in its own isolated domain of forest. All seven of the previously known species are endangered or vulnerable. This seclusion makes it vital to distinguish species and get them added to the conservation priority list, Lawson says. Then, governments and organizations can begin protecting the region that the new, potentially endangered animal calls home.

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Are Your Cats Having Fun Or Fighting? Here Are Some Ways To Tell

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Are your cats play fighting or fighting fur real?

It turns out that certain behaviors in domestic cats could be telltale signs that an interaction is friendly, aggressive or something in between, researchers report January 26 in Scientific Reports.

“It is a question we hear a lot from cat owners,” says cat behavior expert Mikel Delgado of Feline Minds, a cat behavior consulting company in Sacramento, Calif., who was not involved in the study. “So I was excited to see that researchers are taking on this topic.”

Scientists have studied cats’ social relationships — both with other cats and humans — but it can be tricky to tell whether two cats are playing or fighting, says veterinarian and cat behavior researcher Noema Gajdoš-Kmecová of the University of Veterinary Medicine and Pharmacy in Košice, Slovakia (SN: 9/23/19).

Sometimes cat owners miss the signs of a tense relationship because they think their pets are just playing, which can lead to stress and illness in the animals, she says. Other times, owners rehome their cats after incorrectly assuming their pets are fighting.

To assess and categorize interactions, Gajdoš-Kmecová and colleagues watched about 100 videos of different cats interacting in pairs. After viewing around one-third of the videos, Gajdoš-Kmecová identified six types of behaviors, including wrestling and staying still. She then watched all of the videos and noted how often each cat exhibited one of the specified behaviors, and for how long. By running statistical analyses on the behaviors, she pinpointed three types of interactions between the cat pairs: playful, aggressive and intermediate.

To confirm the outcome, other members of the team also watched the videos and classified each interaction between felines.

Some clear connections emerged. Quietly wrestling, for instance, suggested playtime, whereas chasing and vocalizations, like growling, hissing or gurgling, implied aggressive encounters.

Intermediate interactions had elements of both playful and aggressive encounters, but especially included prolonged activity of one cat toward the other, such as pouncing on or grooming its fellow feline. These in-between encounters could hint that one cat wants to keep playing while the other doesn’t, with the more playful cat gently nudging to see if its partner wants to continue, the authors say.

This work provides initial insights into cat interactions, Gajdoš-Kmecová says, but it’s just the start. In the future, she plans to study more subtle behaviors, like ear twitches and tail swishes. Both Gajdoš-Kmecová and Delgado also stress that one contentious encounter doesn’t necessarily signal a cat-astrophic relationship.

“This is not just about one interaction,” Gajdoš-Kmecová says. Owners “really should look into the different, multiple interactions in multiple periods of life of the cats and then put it into context.”

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