To a hippopotamus, a wheeze and a honk means more than just ‘hello!’
News and notes about science
Hippopotamuses are some of the most unfriendly creatures in the animal kingdom.
“Apart from mosquitoes, they are the most dangerous animal in Africa, the ones that kill the most people,” said Nicolas Mathevon, a professor of animal behavior at the University of Saint-etienne in France. “People underestimate them. They swim very fast and don’t hesitate to attack boats. They are in the water most of the time, but they can move out of the water very fast. Entering their territory can be quite dangerous.”
But you can’t say that hippos don’t give adequate warnings to strangers.
The large mammals make loud noises, and Mathevon and his colleagues have worked out some of what they mean. Their results, published in Current Biology, suggest that hippopotamuses can distinguish friends from acquaintances, and acquaintances from strangers, by the way they sound.
Mathevon and colleagues studied the animals at the Maputo Special Reserve in Mozambique, where several lakes are inhabited by one or more groups, or pods, of hippos. There, the researchers recorded the calls of hippos in seven pods.
In 10 separate experiments, the scientists played recorded calls to the animals using three tests: first by playing a hippo’s voice to its own group, second using a call from a neighboring group in the same lake and finally with the sound of a stranger from another lake. They made videos of all the responses.
Hippos respond to calls by calling back, approaching the caller or marking their territory by defecating while flicking their tails to spread the feces. The animals responded in some way to recorded calls from any group, but the intensity of the response was lowest when they heard recordings of individuals from their own pod and highest when they heard the honk of a distant stranger. The reaction to a call from a neighboring group was little different from that of one from the same group, and only hearing the call of an animal from a pod of strangers provoked territorial marking.
The study may have implications for the preservation of the species. Hippopotamus populations are declining, and the International Union for Conservation of Nature classifies them as vulnerable.
“The finding that hippos show stronger behavioral reactions to the calls of an unknown hippo can be applied to conservation efforts,” said Diana Reiss, an animal behavior researcher and professor of psychology at Hunter College in New York who was not involved in the study. “It may be important and beneficial to habituate hippos that may need to be relocated to other areas for conservation purposes, to the calls of unfamiliar hippos they will be encountering in new locations.”
— Nicholas Bakalar
Two simple tricks that help owls stay in their new homes
As far as wild animals go, the western burrowing owl is a tolerant neighbor to humans. When new houses and roads are built next to the tunnels that they call home, these owls put up with the noise and carry on hunting the insects and rodents that they eat. But the owls are increasingly on a collision course with humanity.
Developers are always looking for more land to build on, and in places like Southern California, that means moving into the owls’ habitats. To date, most builders have displaced owls by collapsing their burrows, forcing them to find a new place to live nearby. Even so, in heavily urbanized environments, the birds often have nowhere to go, putting the species’ future at risk.
As a result, wildlife officials working with developers are increasingly collecting and transplanting the owls to distant new areas that conservationists think will meet their needs. Evidence that this technique works has been thin, though. New research published in the journal Animal Conservation shows it can be very effective if the birds are tricked into believing there are already other burrowing owls near the places where they are transplanted.
Ronald Swaisgood of the San Diego Zoo Wildlife Alliance, a member of the research team that produced the report, knew that developers were setting aside land for displaced birds, but noted that there was little follow-up work on how the owls were doing.
Swaisgood and his team collaborated with the U.S. Fish and Wildlife Service to run an experiment with owls that were on land that was going to be bulldozed in the greater San Diego area.
To understand whether the owl transplants were effective, the researchers set up special doors on the burrows of the colonies that allowed the owls to leave but not return. Once the owls were out, all 44 were collected and moved to a new location that already had burrows for them. To help these translocated owls cope, they were kept in acclimation enclosures for 30 days before being released. Of this group, half were exposed to a bit of trickery.
For half of the birds, the team splattered nontoxic white latex paint on the rocks around burrows in the new location that looked like bird poop. They did this because burrowing owls have a tendency to defecate near burrow entrances, and this technique makes the sites look inhabited. To further support this illusion, an outdoor speaker was set up at these sites to periodically play burrowing owl calls during the week before the animals were released from their acclimation enclosures, and during the following week.
All of this ecological duplicity paid off. The 22 birds that were translocated to sites with white paint and calls quickly settled in while the other 22 owls all wandered off.
— Matt Kaplan
Your body’s thirst messenger is in an unexpected place
Few pleasures compare to a long cool drink on a hot day. As a glass of water or other tasty drink makes its way to your digestive tract, your brain is tracking it — but how? Scientists have known for some time that thirst is controlled by neurons that send an alert to put down the glass when the right amount has been guzzled. What precisely tells them that it is time, though, is still a bit mysterious.
In an earlier study, a team of researchers found that the act of gulping a liquid — really anything from water to oil — is enough to trigger a temporary shutdown of thirst. But they knew that gulping was not the only source of satisfaction. There were signals that shut down thirst coming from deeper within the body.
In a paper published in Nature, scientists from the same lab report that they’ve followed the signals down the neck, through one of the body’s most important nerves, into the gut, and finally to an unexpected place for this trigger: a set of small veins in the liver.
The motion of gulping might provide a quick way for the body to monitor fluid intake. But whatever you swallowed will swiftly arrive in the stomach and gut, and then its identity will become clear to your body as something that can fulfill the body’s need for hydration, or not. Water changes the concentration of nutrients in your blood, and researchers believe that this is the trigger for real satiation.
“There is a mechanism to ensure that what you’re drinking is water, not anything else,” said Yuki Oka, a professor at Caltech and an author of both studies. To find out where the body senses changes to your blood’s concentration, Oka and his colleagues first ran water into the intestines of mice and watched the behavior of nerves that connect the brain to the gut area, which are believed to work similarly in humans. One major nerve, the vagus nerve, fired the closest in time with the water’s arrival in the intestines, suggesting that this is the route the information takes on the way to the brain.
Then, the researchers went one by one and sliced each of the nerve’s connections to different regions in the gut. To their surprise, nothing changed when they cut off contact to the intestines.
Instead, it was the portal veins of the liver — vessels that carry that blood from around the intestine to the filtering organ — whose isolation silenced the messages back to the brain.
— Veronique Greenwood
Frogs without legs regrow leglike limbs in new experiment
African clawed frogs are masters of putting themselves back together, handily regenerating lost tails and hind limbs, when they are tadpoles. But these powers dim with maturity. Wait for an adult frog to regrow a lopped-off limb and you’ll see only a tapered spike, more like a talon than a leg.
Now, a group of scientists have found a way to harness the adult frog’s own cells to regrow an imperfect but functional limb. The researchers placed a silicone cap laden with a mixture of regenerative drugs onto an amputation wound for 24 hours. Over the next 18 months, the frogs gradually regrew what was lost, forming a new leglike structure with nerves, muscles, bones and even toelike projections.
The researchers describe this approach, which builds on earlier research, in a paper published in the journal Science Advances. The process could guide future research on limb regeneration in humans, but it will be challenging to replicate the results in mammals.
“It was a total surprise,” Nirosha Murugan, a researcher at Algoma University in Ontario, Canada, and an author of the paper, said of the complexity of the regrown limb. “I didn’t think we would get the patterning that we did.”
Some aquatic animals have impressive regeneration skills, allowing them to regrow tissue, parts of major organs and even whole limbs. But glassy-eyed, meaty-bodied adults of the African clawed frog, or Xenopus laevis, have none of this regeneration prowess. “They face some of the same limitations as humans do,” said Michael Levin, a biologist who directs the Allen Discovery Center at Tufts University and is an author on the paper. Murugan conducted the research in Levin’s lab.
The researchers made a wearable silicone cap called the Biodome, which was filled with a silk protein hydrogel. Murugan researched all the commercially available drugs known to encourage regeneration before settling on a mixture of five to be loaded into the Biodome and released on the wound.
In 2017, the researchers started what would become an 18-month experiment. On the first day of the experiment, a graduate student at the time, Annie Golding, and a researcher, Quang Pham, created the cocktail of drugs and Biodomes. Murugan — along with a technician, Kelsie Miller, and an undergraduate student, Hannah Vigran — performed 13 hours of surgery on 115 anesthetized female frogs.
At about the four-month mark, the frogs’ limbs began to diverge, depending on which of three experimental groups they were in, Murugan said.
A group of frogs that received no treatment began developing stubby little spikes. And the frogs that wore the Biodome for 24 hours with no medication showed slightly more growth. But the batch of frogs that wore the Biodome laden with the drug mixture, also for just 24 hours, gradually developed something thicker and complex, with nerves, bone and cartilage. The limb even developed protrusions that resembled toes.
— Sabrina Imbler