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Smithsonian Tropical Research Institute
Smithsonian Tropical Research Institute

This Snail's Sex Change Is Triggered by Touch

Smithsonian Tropical Research Institute
Smithsonian Tropical Research Institute

Tropical slipper limpets are pretty unremarkable. They spend most of their lives sitting in one spot under a rock filtering their food out of the water. When it comes time for the limpets to mate, though, things get interesting. 

Compared to their body size, male limpets have some of the most impressive penises in the animal kingdom—almost as long as the snail’s entire body. They don’t hang on to these massive members forever, though. Slipper limpets begin their lives as males and turn into females as they age and grow—a process called sequential hermaphroditism. Their penises slowly shrink and then disappear while their female organs develop. 

A recent study in The Biological Bulletin shows that this dramatic change is set off by a simple touch.

Plenty of animals—including some starfish, crustaceans, and fish—change sex at some point in their lives. The timing of a sex change has to do both with an animal’s size and the company it keeps. Bigger animals can produce and carry more eggs than smaller ones, while sperm production is less size-dependent, so the switch usually happens when an animal reaches a certain size. For many sex-changing animals, there’s also a social factor, and the animals in a mating group or population can “tell” each other when it’s the best time to switch. 

Chemical cues are used by sea snails and other mollusks to warn one another about predators, recognize each other, and choose sites to live, among other things. Rachel Collin, a biologist at the Smithsonian Tropical Research Institute, figured that limpets used similar chemical signals to prompt each other's sex changes, too.

To test that idea, she and intern Allan Carrillo-Baltodano collected small male slipper limpets at Playa Chumical on Panama’s Pacific coast. They paired the snails off and placed them in different cups of seawater that allowed them different degrees of access to any chemical cues their cup mates might release. In some cups, the snails were free to roam around and come in contact with each other. In others, a mesh barrier kept them on separate sides of the cup. Some of the barriers had a finer mesh that only allowed water through, while others were a little wider and let the snails touch each other through the screen. Still other pairs were separated by fine mesh, but the snails were switched from one side of the cup to the other every week, letting them come in contact with their cup mate’s pedal mucus, the gluey substance snails and slugs use to help them move around.

When the limpets were allowed total access to each other, the larger one in each pair grew faster and changed sex sooner than their counterparts that were separated from their partners, while smaller, free-roaming partners delayed their own sex changes longer than the smaller snails in the separated pairs. The snails that were separated by the fine mesh and those that switched sides in their cups changed sex on the same, slower schedules, while the ones that were separated by the wider mesh fell in the middle.

Collin and Carrillo-Baltodano said they expected the sex change to be triggered by chemical cues since limpets are sedentary, but their results suggest that the change “requires some kind of physical interaction that is lost when the snails are separated.” For now, they aren’t sure what it is about physical contact that sets the change in motion. It might have to do with the way one snail positions itself relative to another, or a certain type of physical stimulation. Chemical signals could also still be at work, but ones that are contact-based instead of waterborne.

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Animals
Pigeons Are Secretly Brilliant Birds That Understand Space and Time, Study Finds
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Of all the birds in the world, the pigeon draws the most ire. Despite their reputation as brainless “rats with wings,” though, they’re actually pretty brilliant (and beautiful) animals. A new study adds more evidence that the family of birds known as pigeons are some of the smartest birds around, as Quartz alerts us.

In addition to being able to distinguish English vocabulary from nonsense words, spot cancer, and tell a Monet from a Picasso, pigeons can understand abstract concepts like space and time, according to the new study published in Current Biology. Their brains just do it in a slightly different way than humans’ do.

Researchers at the University of Iowa set up an experiment where they showed pigeons a computer screen featuring a static horizontal line. The birds were supposed to evaluate the length of the line (either 6 centimeters or 24 centimeters) or the amount of time they saw it (either 2 or 8 seconds). The birds perceived "the longer lines to have longer duration, and lines longer in duration to also be longer in length," according to a press release. This suggests that the concepts are processed in the same region of the brain—as they are in the brains of humans and other primates.

But that abstract thinking doesn’t occur in the same way in bird brains as it does in ours. In humans, perceiving space and time is linked to a region of the brain called the parietal cortex, which the pigeon brains lack entirely. So their brains have to have some other way of processing the concepts.

The study didn’t determine how, exactly, pigeons achieve this cognitive feat, but it’s clear that some other aspect of the central nervous system must be controlling it. That also opens up the possibility that other non-mammal animals can perceive space and time, too, expanding how we think of other animals’ cognitive capabilities.

[h/t Quartz]

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The Queen's Racing Pigeons Are in Danger, Due to an Increase in Peregrine Falcons
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Queen Elizabeth is famous for her love of corgis and horses, but her pet pigeons don't get as much press. The monarch owns nearly 200 racing pigeons, which she houses in a luxury loft at her country estate, Sandringham House, in Norfolk, England. But thanks to a recent boom in the region’s peregrine falcon population, the Queen’s swift birds may no longer be able to safely soar around the countryside, according to The Telegraph.

Once endangered, recent conservation efforts have boosted the peregrine falcon’s numbers. In certain parts of England, like Norfolk and the city of Salisbury in Wiltshire, the creatures can even find shelter inside boxes installed at local churches and cathedrals, which are designed to protect potential eggs.

There’s just one problem: Peregrine falcons are birds of prey, and local pigeon racers claim these nesting nooks are located along racing routes. Due to this unfortunate coincidence, some pigeons are failing to return to their owners.

Pigeon racing enthusiasts are upset, but Richard Salt of Salisbury Cathedral says it's simply a case of nature taking its course. "It's all just part of the natural process,” Salt told The Telegraph. "The peregrines came here on their own account—we didn't put a sign out saying 'room for peregrines to let.' Obviously we feel quite sorry for the pigeons, but the peregrines would be there anyway."

In the meantime, the Queen might want to keep a close eye on her birds (or hire someone who will), or consider taking advantage of Sandringham House's vast open spaces for a little indoor fly-time.

[h/t The Telegraph]

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