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Self-Perpetuating Female Salamanders Are Better Off Without Males, Study Finds

Human sex is fascinating, but compared to other animals, the way we reproduce is boring. Take the mole salamander, for example. Some all-female populations of salamanders have figured out a way to make copies of themselves without bothering to involve males. Now, ordinarily, that kind of reproduction shrinks the gene pool and makes animals less able to adapt. But researchers, who published their findings in the Journal of Zoology, say the opposite is true for some mole salamanders, which have complex genes and can regenerate body parts faster than their relatives.

How could an all-female group add to its gene pool? Two words: secondhand sperm. Male salamanders in the genus Ambystona are sloppy creatures, and will leave pools of their genetic material lying around on leaves and twigs. If a female salamander happens to find that sperm, she might just put it to use. And it gets even weirder: that male doesn’t even have to belong to her species. A cloned female could carry DNA from several different species at once—and it’s this capacity that may make her special.

To learn more, researchers collected six blobs of salamander eggs from wetland environments in Ohio. Three of the egg masses were taken from populations of sexually reproducing male and female small-mouth salamanders (A. texanum). The other three egg blobs were collected from all-female (or unisexual) groups in the same area. All the eggs were brought back to the lab and their inhabitants reared to adulthood.

Denton palling around with one of his gifted subjects. Image Credit: Kevin Fitzsimmons, The Ohio State University

Once the salamanders were 10 to 12 months old, the researchers took them out and cut a small piece from each one’s tail. The tail snips from unisexual salamanders were used to test their DNA and identify their ancestry. Now humans, most other mammals, and many salamanders are diploid: that is, each individual has two sets of chromosomes, one from each parent. Salamanders from the no-boys-allowed club, on the other hand, had three sets apiece, taken from two different species (A. laterale and A. jeffersonium).

The researchers monitored the salamanders for weeks, measuring their tails to see if and how quickly they were growing back. A gap soon emerged. After seven weeks, the self-cloning salamanders’ tails were almost completely regenerated. But the small-mouths’ tails wouldn’t finish growing back for another four weeks after that. To put it another way: members of the all-female salamander group regenerated their tails 1.5 times faster than the small-mouths could.

"I don't think we expected it to happen so fast," Ohio State biologist and study co-author Robert Denton said in a press statement.

A salamander’s tail is not just for show; it’s a functional appendage. As juveniles in the water, salamander larvae need tails to propel them through the water in order to evade predators. As adults, they can use their tails to distract opponents long enough to get away. So the ability to grow back a tail quickly is kind of a huge advantage.

"They get injured a lot," said biology student and study leader Monica Saccucci. "If you can't regenerate, you're dead.”

Saccucci, Denton, and their colleagues are quite impressed with the unisexual salamanders, but remain unsure of how they’re doing it. Is having sex with yourself the key to getting ahead? Is it the fact that each salamander lady is a hybrid? Are their ancestral species just really cool? Is it all those chromosomes they’re hoarding?

"Ideally, we'd love to compare unisexuals with different numbers of genomes from different species against those sexual species," Denton told mental_floss in an email. But he does suspect that the single-sex lifestyle has something to do with it.

"We do have other physiological data (locomotor endurance on treadmills) that suggests that unisexuals are different as a group when compared to multiple sexual species, which might suggest that the regeneration difference here is due more to polyploidy than genome composition," Denton said. "Overall, there is a great deal of work to be done disentangling the strange genomic makeup of these animals."

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Animals
25 Benefits of Adopting a Rescue Dog
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According to the ASPCA, 3.3 million dogs enter shelters each year in the United States. Although that number has gone down since 2011 (from 3.9 million) there are still millions of dogs waiting in shelters for a forever home. October is Adopt a Shelter Dog Month; here are 25 benefits of adopting a shelter dog.

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Brooklyn Museum, Charles Edwin Wilbour Fund, 37.406E
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Art
New Smithsonian Exhibit Explains Why Felines Were the Cat's Meow in Ancient Egypt
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Brooklyn Museum, Charles Edwin Wilbour Fund, 37.406E

From bi-coastal cat cafes to celebrity pets like Lil Bub, felines are currently enjoying a peak moment in popular culture. That’s part of the reason why curators at the Smithsonian’s Arthur M. Sackler Gallery—which will re-open to visitors on Saturday, October 14, following a 3-month closure—decided to dedicate a new exhibition to ancient Egypt’s relationship with the animals.

Divine Felines: Cats of Ancient Egypt” looks at the cultural and religious importance of cats, which the Egyptians appreciated long before YouTube was a thing and #caturday was a hashtag. It's based on a traveling exhibition that began at the Brooklyn Museum in New York City. On view until January 15, 2018, it's one of several exhibits that will kick off the grand reopening of the Smithsonian’s Freer and Sackler galleries, the conjoined national museums of Asian and Middle Eastern Art.

The Freer has been closed since January 2016 for major renovations, and the Sackler since July 2016 for minor ones. The upgraded institutions will make their public debut on October 14, and be feted by a free two-day festival on the National Mall.

Featuring 80 artworks and relics, ranging from figurines of leonine deities to the tiny coffins of beloved pets, "Divine Felines" even has a cat mummy on loan from the Smithsonian’s National Museum of Natural History. These objects span from the Middle Kingdom (2008 to 1630 BCE) to the Byzantine period (395 to 642 CE).

An ancient Egyptian metal weight shaped like a cat, dating back to 305 to 30 BCE, on view at the Smithsonian’s Arthur M. Sackler Gallery
Weight in Form of a Cat, 305 to 30 BCE, Bronze, silver, lead
Brooklyn Museum, Charles Edwin Wilbour Fund, 36.114

The term “cat” is used loosely, as the Egyptians celebrated domestic mousers and fearsome predators alike.

“The Egyptians were close observers of nature, so they were observing cat behaviors,” Antonietta Catanzariti, the exhibition's in-house curator, tells Mental Floss. “They noticed that cats and lions— in general, felines—have aggressive and protective aspects, so they associated those attributes to deities.”

The ancient Egyptians viewed their gods as humans, animals, or mixed forms. Several of these pantheon members were both associated with and depicted as cats, including Bastet, the goddess of motherhood, fertility, and protection; and Sakhmet, the goddess of war and—when appeased—healing. She typically has a lion head, but in some myths she appears as a pacified cat.

A limestone sculptor's model of a walking lion, on display at the Smithsonian's Arthur M. Sackler Gallery.
Sculptor's Model of a Walking Lion, ca. 664 to 630 BCE, limestone
Brooklyn Museum, Charles Edwin Wilbour Fund, 33.190

While Bastet was a nurturer, Sakhmet—whose name means “The Powerful One”—could use her mighty force to either slay or safeguard humanity. These characterizations are typical of the ancient Egyptian worldview, which perceived the universe in dualistic terms. “There’s always a positive and a negative,” Catanzariti explains.

Contrary to popular belief, however, ancient Egyptians did not view cats themselves as gods. “The goddess Sakhmet does have the features as a lion, or in some cases as a cat, but that doesn’t mean that the Egyptians were worshipping cats or lions,” Catanzariti says. Instead, they were simply noting and admiring her feline traits. This practice, to an extent, also extended to royalty. Kings were associated with lions and other large cats, as they were the powerful protectors of ancient Egypt’s borders.

These myriad associations prompted Egyptians to adorn palaces, temples, protective amulets, ceremonial vessels, and accessories with cat images. Depending on their context, these renderings symbolized everything from protection and power to beauty and sexuality. A king’s throne might have a lion-shaped support, for example, whereas a woman’s cosmetics case might be emblazoned with a cat-headed female goddess of motherhood and fertility.

An ancient Egyptian figurine of a standing lion-headed goddess, on display at the Smithsonian's Arthur M. Sackler Gallery.
Figurine of a Standing Lion-Headed Goddess, 664 to 630 BCE, Faience
Brooklyn Museum, Charles Edwin Wilbour Fund, 37.943E

While cats were linked with heavenly figures and kings, they were also popular domestic pets. Their ability to catch vermin made them an important addition to households, and owners loved and anthropomorphized their pets just like we do today.

Egyptians often named, or nicknamed, their children after animals; Miit (cat) was a popular moniker for girls. It's said that entire households shaved their eyebrows in mourning if a house cat died a natural death. Some also believe that cats received special legal protection. (Not all cats were this lucky, however, as some temples bred kittens specifically to offer their mummified forms to the gods.) If a favorite cat died, the Egyptians would bury them in special decorated coffins, containers, and boxes. King Tutankhamen, for example, had a stone sarcophagus constructed just for his pet feline.

An ancient Egyptian bronze cat head adorned with gold jewelry, on display at the Smithsonian's Arthur M. Sackler Gallery.
Cat's Head, 30 BCE. to third century CE, bronze, gold
Brooklyn Museum, Charles Edwin Wilbour Fund, 36.114

“Divine Felines” breaks down these facts, and more, into five thematic sections, including “Cats and Kings"; “Cats and Gods”; “Cats and Death”; “Cats and Protection”; and “Dogs as Guardians and Hunters.” Yes, there’s also an exhibition section for dog lovers—“a small one,” Catanzariti laughs, that explains why canines were associated with figures like Anubis, the jackal-headed god of mummification and the afterlife.

Did the ancient Egyptians prefer cats to dogs? “I would say that both of them had different roles,” Catanzariti says, as dogs were valued as hunters, scavengers, and guards. “They were appreciated in different ways for their ability to protect or be useful for the Egyptian culture.” In this way, "Divine Felines" is targeted to ailurophiles and canophiliacs alike, even if it's packaged with pointed ears and whiskers.

An ancient Egyptian cat coffin, on display at the Smithsonian's Arthur M. Sackler Gallery.
Coffin for a Cat, 664 to 332 BCE, or later, Wood, gesso, paint, animal remains
Brooklyn Museum, Charles Edwin Wilbour Fund, 37.1944Ea-b

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