In a study recently published in Neuron, researchers found that cocaine use changes the DNA in mouse brains, specifically in the brain regions associated with reward. After consuming cocaine, the DNA in their brain cells had different chemical modifications known as epigenetic changes. These epigenetic changes also altered the types of RNAs the cells made through splicing. In this process, pieces of genes are left out or added in to create different RNAs that create different proteins.

Scientists have known RNA splicing is particularly important for neurons, and the researchers behind this mouse study saw many epigenetic and splicing changes after the mice consumed cocaine. Then, they artificially recreated one specific epigenetic change at a gene called Srsf11. This led Srsf11 to be spliced differently. However, Srsf11 is also a gene that controls splicing across the genome, meaning that changes to it had ripple effects in the mice. This one change also altered splicing across a few hundred other genes, some of which were previously implicated in substance use disorders. Most interestingly, the mice with the modified version of Srsf11 self-administered more cocaine, showing that these sorts of changes in the brain may underlie addiction.

Some researchers argue that increasing the body of evidence for the biological basis of substance use disorders reduces stigma against people who use substances, though the effectiveness of this in public messaging is debated. Regardless, though we continue to see evidence that substance use disorders are biologically-driven, there are currently no approved drugs to treat the overuse of cocaine. Epigenetics and RNA splicing may be promising targets for future medical interventions.

Staring at a comb jelly, it's not very obvious which end is mouth and which is butt.

A quick search of "comb jelly" shows how many of us get it wrong. We often depict comb jellies butt up (like the image for this article), though they tend to swim and rest mouth up. Comb jellies look so much like a marine bedsheet ghosts, it's understandable we'd assume the domed part is the mouth side instead of the butt.

If you keep watching a comb jelly, you may be able to tell which end is the butt, because you'll see it eat and you'll also see it poop. However, unless you have a microscope trained on the jelly's rear end, you wouldn't necessarily be aware of a vanishing act you just witnessed. A few years ago, researchers discovered that the warty comb jelly (Mnemiopsis leidyi) has a disappearing anus. Every time a warty comb jelly needs to poop, the outer skin and the digestive system fuse to form an opening. Then after the poop is completed, that nexus vanishes without a trace.

Making and unmaking an anus sounds like such an ordeal, you might imagine comb jellies poop rarely. However, comb jellies are constant consumers, and thus frequent poopers. Exactly how often the comb jelly poops scales with its body size. In a large adult comb jelly, the transient anus appears and disappears about every hour. The tiniest of comb jellies, only a fifth of a centimeter long, form and then reabsorb their anuses every 10 minutes. Still, even these tiny comb jellies spend most of their time without an anus. This vanishing act is fast. Appearing, pooping, and disappearing takes the anus just a few minutes.

The transient nature of the comb jelly anus was discovered in 2019 by Sidney L. Tamm at the Marine Biological Laboratory. However, we've known since 1850 that comb jellies have an anus, unlike many similar looking but not closely related species. Comb jellies are their own group separate from jellyfish, who have no anuses and thus poop out their mouths. An anus was in fact one of the key differences that led invertebrate zoologist Libbie Hyman to reclassify comb jellies as distinct from jellyfish in 1940, well before genome sequencing confirmed their evolutionary distance.

Prior to the discovery of the transient anus, we didn't just think comb jellies had anuses, but that they might have two. A comb jelly has a pair of structures on its rear end known as anal lobes. Both of these anal lobes swell prior to pooping, but one swells more than the other. The anus always appears on the more swollen side, while the less swollen side remains anus-less. All of the poop then moves towards the more swollen side to be ejected out of the new anus. For an individual comb jelly, it's also always the same side that gets more swollen, giving them a sort of butt "handedness". Stranger still, this "handedness" is the only feature that breaks the comb jelly's radial symmetry.

Comb jellies are the only creatures so far known to have transient anuses. Though if any organism was going to have one, it's not too surprising it's the comb jelly. Comb jellies are anatomical trailblazers. They have a nervous system and muscles, but theses systems have very different biology from all other animals. Comb jelly genetics even indicate that their neurons and muscles evolved entirely separately. So why wouldn't comb jellies have their own way to have a butt?

Comb jellies are also some of the most plastic organisms we know of. Cut a comb jelly in half and it can completely rebuild its body in just four days, not even leaving a scar behind. If being sliced in half is just an off week, creating and reabsorbing an anus dozens of times per day may not be such a big deal.

Though comb jellies are alone in having disappearing anuses, the invertebrate world is full of strange butts. The face mite, an arachnid that is exactly what it sounds like, has lost its butt. In its fleeting 16 day life, it feasts but never poops once. Some scorpions join the face mites as butt-less arachnids. Scorpions can drop their tails to escape being eaten, but woefully sacrifice their anuses in the process.

Among the other weird butts scuttling around the ocean, there are species that breathe through their anuses, including sea cucumbers, whose anuses are also homes for fish. The ocean’s other strange symbiotic butt, or butts rather, belongs to the worm Ramisyllis multicaudata, which lives inside a sea sponge. With its head buried deep down in its host, the hundreds of butts of the worm’s branching body poke out like a reverse hydra.

The disappearing anus is just one of many recent developments in our understanding of comb jelly biology. Marine biologists have studied wild comb jellies for centuries, but recently scientists have succeeded in growing comb jellies in the lab. Comb jellies are well on their way to becoming an exciting new research organism. Because they do everything so differently, studying comb jelly biology could help find creative solutions to human biological problems. And as comb jellies pop up in more labs around the world, we might also learn a little more about what it means to have a disappearing butt.

Our DNA collects different chemical modifications know as epigenetic changes. Some of these are age-related and make up our “epigenetic age.” Someone’s age in years and epigenetic age don’t always agree, and in humans faster epigenetic aging has been associated with increased disease risk and shorter lifespan. However, we’re still learning what influences epigenetic age in humans and other animals. 

A recent study published in eLife shows that social status is the best predictor of epigenetic age in male baboons. This faster aging isn’t true for female baboons, who inherit their ranks from their mothers. Therefore, the researchers posit it’s not the rank of male baboons that accelerates their aging. Instead, it’s the process of climbing the social ladder. So why would social climbing among baboons be associated with faster aging? 

For male baboons, rising in rank means fighting for it, and their rank can change in their adult life. Not only does high status increase epigenetic age, but dropping in status can reverse accelerated aging as well. This “live fast, die young” way of life may still be worth it, from an evolutionary perspective. Despite the cost, high-ranking males are still more likely to reproduce. Social pressures among humans don’t align with those of baboons. Nevertheless, learning how other primates age and why can help us better understand the factors that contribute to aging in humans.