Erin Southerland

August 2, 2024 by Erin Southerland

The Moon Snails Neverita duplicata and Euspira heros: Cannibal Predators of the Sea! … who also enjoy a nice algae salad

by Sabrina Spiher Robinson and Tim Pearce

Imagine you’re a clam, hanging out in your cozy little hole under shallow ocean water, with your siphon out, just filtering lunch out of the water current, happy as a…you. Then, all of a sudden, something flips you gently out of that hole.

You pull in your siphon and your foot, clamp shut your valves. You’re pretty tough to get open, strong adductor muscles keep your two shells held tightly together, and you’ve survived danger by closing up shop and waiting before. And nothing seems to be trying to pry you open, even though something has wrapped itself around you, and is now pulling you down into the sand with it. Then:

scrape scrape scrape

Or imagine you’re a young moon snail, Neverita duplicata – one of the most common species of moon snails that live on the eastern seaboard of North America. You’re a gastropod with a lovely round grayish shell, such that people call it a “shark eye,” and you’ve got a huge foot that can come out of that shell and cover almost all of your body – or all of your prey’s body! But at the moment you’re just cruising along the sand, slurping at a bit of detritus. Suddenly, you’re enveloped by something. You instinctively pull your body into your shell and tightly close your door-like operculum for safety. Then your aperture is covered by…something familiar? Then:

scrape scrape scrape

It doesn’t matter how tightly the clam clamps, or how mighty the young snail’s foot, both are going to come to the same fate, slowly.

scrape scrape scrape

Eventually, your shell is penetrated. A rasping radula – a mollusk’s organ containing its teeth – has bored a hole through your shell with the help of a gentle acid secreted by a gland by the mouth, and then you feel a burning: gastric juices are being pumped through the hole to begin to digest your flesh. Your killer begins to slurp you up, right where you lie, wrapped up in their hug, as you’re slowly eaten alive.

The young moon snail might have figured out who its killer was before the end: that’s how it eats too. The thing is, moon snails are cannibals, the larger preying on the smaller.

There are hundreds of kinds of moon snails all over the world, but the ones that are probably most familiar to beach goers on the eastern coast of the USA are two species also commonly called “shark eyes” – Neverita duplicata and Euspira heros. From the top, they’re hard to tell apart (the spire on E. heros is a little pointier than on N. duplicata) but once you flip them over, it becomes easy to distinguish them: N. duplicata, the Atlantic moon snail, has a big callus over its umbilicus, and E. heros, the Northern moon snail, doesn’t. Technically, only the Atlantic moon snail has a shark eye shell, but since they’re often mixed up with Northern moon snails, the term shark eye is sometimes applied to them too.

N. duplicata, left; E. heros, right. *Photo credit: Sabrina Spiher Robinson*

These two moon snails aren’t the only marine gastropods that drill their prey and digest them alive to suck them up for dinner – lots of marine gastropods are predatory drills. But moon snails have distinct boreholes that allow people to identify when a shell has been bored specifically by a moon snail – scientists can even tell the difference between the Atlantic and Northern species’ holes. These “countersunk” holes look like little funnels, wider on the outside of the shell than on the inside. Other kinds of drilling snails leave behind straight-sided holes.

These unique boreholes allow scientists to track the evolution of moon snails from the Miocene to recent times. One group of researchers found that moon snail cannibalism might have driven a kind of coevolution between and among moon snail species. Because one moon snail can make dangerous prey for a fellow moon snail predator, over time moon snails seem to have learned to drill other moon snails at a spot on their shells that allowed the predator to cover the prey’s entire aperture, preventing the strong foot of their prey from fighting back. This means boring through a thicker part of the shell, however, so it takes longer to hold down and bore through the prey snail’s shell. But the record of natural selection in fossils throughout time suggests the added cost must be worth the benefit of moving target drilling zones. Meanwhile, small moon snails almost always lose out to larger ones when attacked, so both N. duplicata and E. heros have evolved to get bigger and bigger over time – although a bigger snail is also a more enticing snack target. Same-sized moon snails don’t even bother to attack one another, suggesting that a fellow moon snail is just too dangerous a prey when the winner of the battle between snails is a toss-up. As evidence that these are often battles between predator and prey snails, there are many incomplete boreholes found – a moon snail started attacking another moon snail, but only managed to get the job halfway done before the prey moon snail escaped. [1]

To be fair, moon snails aren’t just vicious cannibals – they also enjoy the snail equivalent of a nice salad. Another study that analyzed the tissues of moon snails revealed that their bodies have the chemical signatures of omnivores. The technique is called stable isotope analysis, wherein scientists use the ratio of carbon and nitrogen isotopes in an animal’s body to determine its diet, in broad terms. Carbon exists in three isotope forms, meaning the number of protons is the same in all three atoms, but the number of neutrons is different in each (carbon-12, carbon-13, and carbon-14); Nitrogen also has three isotope forms, nitrogen-14, nitrogen-15, and nitrogen-16. The vast majority of carbon on Earth is carbon-12, which is a stable isotope, as is carbon-13, meaning they do not decay over time; nitrogen-14 and -15 are stable, and make up the vast majority of nitrogen atoms. Different plants and animals have different ratios of carbon and nitrogen isotopes. The ratios of isotopes in plants and animals differ and these differences transfer to the body of the consumer, and so the isotope ratios of a meat-eating animal will differ from those of a vegetarian animal, and an omnivorous animal will be different again. Scientists were surprised to find that wild moon snail isotopes suggested they also ate non-animals, so to check their findings they fed captive moon snails nothing but clams, and then tested their isotopes – which looked exactly as one would expect in an all-meat diet. Apparently the wild moon snails were actually eating things other than meat, probably algae. This was a big deal, since so much of the literature on moon snails is about their predatory drilling! [2]

Moon snail shells are a relatively common find on east-coast beaches (and another moon snail, Euspira lewisii, is a common find on the west coast), but if you’re at the beach this summer, there’s more to look for than just shells – moon snails also leave behind very distinctive egg nests, often called “sand collars.” The fertilized female snail nestles into a little hole in the sand (as all moon snails do during the day when they’re not feeding) and produces a sheet of mucus, which she mixes with sand and pushes up to the surface, as she does so, the sheet curls around her shell and eventually right around to form a ring. This fusion of mucus and sand grains solidifies, she attaches her thousands of eggs to it, and then covers those with another layer of mucus and sand. Once the eggs are ready to hatch after a few weeks, when the next high tide comes along the eggs let go thousands of little larvae called veligers, which will drift off to finish developing into baby snails who will eventually settle into the intertidal zone and start lives for themselves. Once the eggs hatch, the collar becomes brittle and disintegrates, but if you find one that’s still plastic-y on the beach, leave it! There are thousands of tiny baby vicious predators in there waiting to hatch! Awww.

*A sand collar full of shark eye eggs. Image credit: Blenni, Public domain, via Wikimedia Commons.*

Sabrina Spiher Robinson is Collection Assistant for the Section of Mollusks and Tim Pearce is Head of the Section of Mollusks at Carnegie Museum of Natural History.

References

[1] Gregory P. Dietl and Richard R. Alexander, Post-Miocene Shift in Stereotypic Naticid Predation on Confamilial Prey from the Mid-Atlantic Shelf: Coevolution with Dangerous Prey PALAIOS Vol. 15, No. 5 (Oct., 2000), pp. 414-429

[2] Casey MM, Fall LM and Dietl GP, You Are What You Eat: Stable Isotopic Evidence Indicates That the Naticid Gastropod Neverita duplicata Is an Omnivore. Front. Ecol. Evol. 4:125. (2016) doi: 10.3389/fevo.2016.00125

The Busyconidae Whelks, Homebodies of the East Coast

by Sabrina Spiher Robinson and Tim Pearce

We try not to have strong favorites among the mollusks of the world in the CMNH Section of Mollusks, but it’s hard not to love the whelks. They leave behind big, beautiful shells for shell collectors on our east coast and Gulf beaches; they’re instantly recognizable as a family— Busyconidae — and pretty easy to tell apart at the species level by an amateur. Some of the species are sinistral, left-coiling snails, which are otherwise rare among gastropods. They live long and move slowly, reminding us all that slow and steady is an optimal way to approach life. They taste good! The traditional Italian American dish scungilli is often described as “conch,” but conchs only live in our warm southern waters, and what is usually sold in American markets for scungilli is actually whelk meat. (In Italy, they also eat sea snails, under a lot of different names, but the Mediterranean has different families of marine gastropods.)

three view of a lightning whelk — *The lightning whelk,* Sinistrofulgar perversum, a left-coiling gastropod. Public domain, via Wikimedia Commons.

Now, whelks are maybe not the most sophisticated of marine snails: unlike some gastropods with eye stalks and relatively good sight abilities, whelks have eye spots, which don’t do much more than detect light and dark. Studies of their sense of smell reveal them to have a tenuous ability at best to follow scent trails of prey in the water, and they’ve been observed just kind of slowly zig-zagging back and forth in the mud, apparently hoping to run into a clam. Once they find a clam, some whelks wedge the edge of their own shell between the valves of their prey, and just pry for as long as it takes to pop it open. Other species of whelk rock the edge of their own shells back and forth against the opening of a bivalve, slowly chipping its valves apart.

I mean, look: it isn’t much, but it’s honest work. Whelks are just a great family of sea snails. And Busycon whelks are endemic to the east coast of North America, meaning they’ve only ever been found here. Hometown heroes, if you will.

Our east coast whelks are committed homebodies partly because they evolved relatively late among mollusk families, in the Oligocene, a period spanning from 33.9 – 23 million years ago. The family Busyconidae first emerged in the fossil record in the Mississippian Sea, which had been a shallow extension of what is now the Gulf of Mexico that reached far inland along the route of what is now the Mississippi River. At the end of the Oligocene, the planet’s climate cooled and as ice formed at the poles, sea levels fell, eliminating this inland sea in North America — the whelks then found themselves in the Gulf.

Mollusks have existed on Earth clear back to the Cambrian Era, 540 million years ago. Most modern marine gastropod families began evolving earlier than the Busycons, which meant they were around when all the continents on Earth were one giant supercontinent called Pangea. But Pangea had already broken apart before the Busycons appeared in the fossil record.

Now, here’s the thing, if you are a marine gastropod only suited to shallow, intertidal waters, and you come into being along the coast of a supercontinent, given enough time, your family can spread around the entire coastline of that supercontinent. Then, as it begins to break up, your populations break up with it, and in a few dozen millions of years, your family has populations all over the Earth. But if you are a marine gastropod only suited to shallow, intertidal waters, and you come into being when the North Atlantic has already split from Europe, your family can’t make it across the open sea to go anywhere else. And so, the Busycon family of whelks found themselves in the Gulf of Mexico, near the shore, and began to spread from there, east and west, south and north, until today they exist from the Yucatan Peninsula up to about Cape Cod (it gets too cold for them further north).

five views of a knobbed whelk — *Knobbed whelk,* Busycon carica. H. Zell, CC BY-SA 3.0, via Wikimedia Commons.

Buccinidae whelks, however, can handle arctic cold. They first evolved in the Northeast Pacific Ocean, and they eventually spread along the coastlines across the Bering Strait and down onto the North American west coast, across the Canadian Arctic to the North American east coast and the European eastern Atlantic. They’ve actually made it almost everywhere! But Buyscons can’t take that kind of cold.

There are other factors that limit their spread, one is the ocean currents around the Gulf and western Atlantic. Although Cuba is just 90 miles from the Florida Keys, whelks, which are plentiful in Florida, have never managed to cross the Gulf Stream to colonize Cuba. But one of the main things that keep Busycon whelks from getting anywhere is that, unlike most marine mollusks, they never have a free-swimming larval form, in which they could disperse more widely on ocean currents. Most marine snails have a life cycle that starts with an egg and then proceeds after hatching to a free-swimming larva. Basically, most baby marine mollusks are plankton. And in this state, they can float around and sometimes disperse pretty far afield on ocean currents. As long as they end up in suitable habitat when it’s time for them to metamorphosize into their adult forms, marine mollusks can theoretically end up living hundreds of miles from where they were spawned.

But whelks don’t have this free-swimming period in their youth. Adult females are inseminated directly by males and then lay strings of egg cases (which are also reliably common finds on our eastern beaches) in which the little baby whelks grow and hatch as fully formed miniature snails. Then they just crawl off.

knobbed whelk egg case — *The egg case of a knobbed whelk,* Busycon carica. Gtm at en.wikipedia, Public domain, via Wikimedia Commons.

And they’re not very fast crawlers, even for snails. Whelks make their living by eating bivalves, but they’re never in a hurry to find them — in multiple observational studies over many decades, no one has ever seen a Busycon whelk move further than 150 meters in a day, and those go-getters were the outliers; many days whelks barely move at all. Many factors conspire to keep whelks close to their birthplace.

*The channeled whelk,* Busycotypus canaliculatus. Credit: Skye McDavid, CC BY-SA 4.0, via Wikimedia Commons.

Whelk populations are so localized that some researchers think it’s important to identify and treat separately groups of whelks in distinct geographic locations not at all far from each other. In 2022, several scientists at the Virginia Institute of Marine Science (VIMS) published a paper on channeled whelks (Busycotypus canaliculatus) documenting their genetic diversity in different geographic locations. They did this as part of a study of the channeled whelk population in general, to recommend how to manage the whelk fishery. (Whelks are increasingly harvested and sold as “conch” – and sometimes as clam strips!) In America, individual states manage their own fisheries of all kinds, but this isn’t always done well. In order to keep the fishing of any species (fish, mollusk, crab, shrimp, what have you) productive and sustainable, it’s important not to take more from the sea than can be replenished, and not to take animals that haven’t lived long enough to have reproduced (which is why some fisheries have size limits, as a proxy for the age and sexual maturity of the animal being harvested). But without good data on population size as well as age and size at sexual maturity, effective management and limit setting is basically impossible, and too often states don’t err on the side of caution. When allowable takes are too large, or allowed to include juvenile animals, the population of the fishery will plummet, and this has happened in different places and different times among the whelks. So, the VIMS project was meant to contribute data to help manage the whelk fisheries along the east coast sustainably.

The VIMS scientists caught whelks in ten different locations, from Buzzards Bay in Massachusetts down to Charleston, South Carolina, and sequenced their DNA. They found significant genetic divergence between the three sampled populations from the Carolinas and the populations in Virginia and north. But the scientists also found pretty big divergences across all the locations, even in populations as geographically close to one another as Virginia Beach, VA, and the Virginia Eastern Shore, about a hundred miles away across the mouth of the Chesapeake Bay.

Morphologically, all these whelks look pretty much alike, but genetically, they’re very isolated and distinct populations, with very little breeding among locations. Busycon whelks stay so close to home that each of their little geographically specific populations genetically diverge from one another since they never get far enough to meet and mate with whelks in other relatively close locations. The VIMS authors suggested that different whelk populations in different places might require different fishery management based on size at age of maturity, which seemed to change across genetically different populations. And so, it isn’t as simple as managing the “whelk fisheries on the east coast,” or even the “whelk fisheries in Virginia.” Because Channeled whelk populations are so isolated from one another, they might need to be managed as fisheries in Charleston, SC and Ocean City, MD, and so forth, specifically. [1]

After all that, I should tell you, though, that there is one exception to this east coast endemic story: at some point about a hundred years ago, a population of channeled whelks was introduced to San Francisco Bay. They’ve been prospering there ever since, but they can’t spread any further on the west coast because the water outside the bay is too cold for them. That’s an extremely genetically isolated population, in an unusual environment for Busycon whelks – maybe someday it might become distinct enough from its east coast forebears to become its own species?

[1] Askin, Samantha E.; Fisher, Robert A.; Biesack, Ellen E.; Robins, Rick; and McDowell, Jan, Population Genetic Structure in Channeled Whelk Busycotypus canaliculatus along the U.S. Atlantic Coast (2022). Transactions of the American Fisheries Society. DOI: 10.1002/tafs.10374

Sabrina Spiher Robinson is Collection Assistant for the Section of Mollusks and Tim Pearce is Head of the Section of Mollusks at Carnegie Museum of Natural History.

Mineral Gazing

by Debra Wilson

Have you ever gazed up at the sky and noticed a cloud that looks like a face, or an animal, or an object? You can apply the same concept when you visit Hillman Hall of Minerals and Gems! Many minerals on display have nicknames because of how they resemble certain animals, objects, or even characters from movies or TV shows. As you walk through the exhibits, let your imagination wander and search for minerals that look like things. Here are some to get you started.

Silver mineral that looks like an American flag — *“The Flag” – Silver in the Native Elements case of the Systematic Mineral Collection*

Image of the American flag that says "we here highly resolve that these dead shall not have died in vain...rememeber Dec. 7th!" — *Photo credit: Allen Saalburg, Public domain, via Wikimedia Commons.*

Nessie silver mineral — *“Nessie” – Silver in Minerals from the Former Soviet Union exhibit*

Loch Ness monster sculpture in the water — *Photo credit: Immanuel Giel, Public domain, via Wikimedia Commons*

snowball calcite on quartz — *“Snowball” – Calcite on quartz in the Maramures District of Romania exhibit*

snowball held in mitten-covered hands — *Photo from Shutterstock.*

Inch Worm berthierite on quartz — *“Inch Worm” – Berthierite on quartz in The Maramures District of Romania exhibit*

photo of an inch worm — *Photo credit: gbohne from Berlin, Germany, CC BY-SA 2.0, via Wikimedia Commons*

The Scream septarian concretion — *“The Scream” – Septarian concretion in the Weathering Processes exhibit*

"The Scream" painting — *Image credit: Edvard Munch, Public domain, via Wikimedia Commons*

the oyster natrolite on quartz — *“The Oyster” – Natrolite on quartz in the Deccan Plateau of India exhibit*

oyster shell with a pearl — *Photo from Shutterstock.*

French fries laumontite — *“French Fries” – Laumontite in Masterpiece Gallery*

cup of French fries — *Image by ha11ok from Pixabay*.

As you enter Hillman Hall, check out the minerals in the Entrance Cube, their nicknames are on the labels. There are many more minerals on display throughout the hall that have acquired nicknames. Here’s just a handful of other nicknames for minerals in the exhibits, see if you can find them. Good luck and enjoy your mineral gazing!

Nickname	Exhibit
The Bat	Igneous Rocks
Polar Bear	Weathering Processes
Sea Slug	The Maramures District of Romania
The Chariots	The Maramures District of Romania
Smog Monster	The Maramures District of Romania
Sea Serpent	Pennsylvania Minerals and Gems
Pine Trees On a Cliff	Oxides
BBQ Chips	Masterpiece Gallery
Cookies and Cream	Masterpiece Gallery

Debra Wilson is Collection Manager for the Section of Minerals at Carnegie Museum of Natural History.

Life Lessons from Dead Birds

by Pat McShea

The title of this post, “Life Lessons from Dead Birds,” is a phrase I use to summarize my long career as an educator at Carnegie Museum of Natural History. For more than 38 years I managed what is now called the Learning Collection, an enormous assemblage of artifacts, rocks, minerals, fossils, and preserved plants and animals, all dedicated to regional educational use through loans to teachers and other educators. The bird-focus of the summary phrase reflects both the numerous avian materials in the Learning Collection and my preference to use some of those items whenever I had the opportunity to work with students.

belted kingfisher taxidermy mount study skin, wing, and skull — *Belted Kingfisher physical materials in the Learning Collection include a taxidermy mount, study skin, spread wing, and skull.*

There was reasoning behind my bird bias. For natural history topics as narrowly focused as physical feeding adaptations, and as wide ranging as energy flow through ecosystems, bird examples provided students, elementary, middle, or high school level, with the chance to make their own topically relevant observations using common bird species around their school grounds, neighborhoods, and homes. My earliest presentations, however, taught me how important it was to address questions from the audience about the unique instructional materials.

The students’ questions never seemed like accusations. Whether the setting was a classroom, an auditorium, or a park pavilion, when I stood before them bearing the preserved remains of a once living bird, they simply wanted to know about my connection to the creature’s death. My denials varied with the specimen in-hand. For the spread wing of a hawk, or the skull of an owl, touchable objects that require occasional replacement because of wear from repeated examinations, I’d explain the specimen’s provenance as salvaged material from road-killed or window-killed wildlife.

“Birds and other wildlife have accidents, and sometimes already dead animals are donated to the museum. Permits and regulations are involved, and as a museum educator, my role in the process is to store the bodies in a freezer until they can be prepared for educational purposes.”

*A Learning Collection storage drawer holds six bird study skins. Clockwise, Great Blue Heron, Pied-billed Grebe (3), American Bittern, and American Woodcock.*

When presentations involved life-like, full body taxidermy mounts, I was able to cite far longer periods of personal separation. These birds are encased in portable display boxes with clear acrylic sides, and when I held them up, I drew the students’ attention to the creature’s pose.

“This bird appears ready to feed or to fly, and it’s been holding that position since long before I began working at the museum. I don’t know how it died, but I can share some information about how it has been preserved.” A gory summary followed, compressing into a few sentences, hours of meticulous work with scalpels, wire, pins, and a bird skin with every feather still attached to its outer surface. “The feathers are real, and the beak, along with some skull bones and leg bones, are still in place. All the body parts that would decay were removed long ago – the eyes, the brain, every internal organ, the muscle tissues. The eyes were replaced with glass replicas, of the proper size, shape, and color, and the skin, with feathers in place, was fitted over a custom-made form shaped just like the bird’s body.”

On some occasions, exploration of a presentation’s main topic was even further delayed because student inquiries shifted from the circumstances behind the authentic wildlife materials to their very purpose. “Why use animal remains at all?” I recall a student once asking.

My attempts to answer such questions came to include a quote from the late Dr. John E. Rawlins, former Curator of the museum’s Section of Invertebrate Zoology, about the critically important reasons for scientific collections to be created, maintained, and expanded. “Specimens are similar to books in libraries, because they are volumes of information that may be re-examined and reaffirmed,” Dr. Rawlins wrote, “But specimens are much more informative than books, because the content of a book is acquired in full by a single type of observation, reading. By contrast, the information content of a specimen is acquired by diverse methods of observation, many of which have not been applied to most specimens, and some of which have not yet been devised or even dreamed of.”

In advocating for the use of similar materials as educational tools, I expressed my hope that their current encounter with selected bird specimens might spark interest in, and even build empathy for, the populations of various wild bird species. As an example of this process, I cited personal experience. Before working at the museum, I was a Volunteer Naturalist at Beechwood Farms Nature Reserve, the headquarters for the Audubon Society of Western Pennsylvania. My first encounter with a bird study skin (the rigid, cotton-stuffed, and eyeless form traditional in scientific collections) occurred during a training session there, when a Pied-billed Grebe specimen was the focus of a presentation. As the study skin was carefully passed among the dozen participants, we were encouraged to examine the bird’s lobed toes, a physical feature that provided hints about the creature’s aquatic lifestyle.

*In carefully examining the study skin of a Pied-billed Grebe, you can learn about the dense down insulation of this aquatic bird.*

On sections of the lower Allegheny, I had observed single Pied-billed Grebes at least a dozen times during winter months, floating placidly just off sections of wooded riverbank, and making regular, 30-second dives beneath the surface. When the study skin reached me, I dutifully examined its toes, but I also used an index finger to gently part the dense pale breast feathers to reveal a layer of much denser gray down beneath them. In that moment, the specimen provided information, different than a photograph or written account, about how the birds I observed on the icy Allegheny stayed warm. This tactile specimen-centered encounter convinced me that preserved bird remains can enhance observations of the species’ more numerous living kin. During the years I managed the Learning Collection this was among the most important concepts I promoted.

Pat McShea is an Educator at Carnegie Museum of Natural History.

Botanists Gone Wild! Perspectives from the Record-Breaking Finish for City Nature Challenge 2024

by Jessica Romano

Every spring people all over the world join in the City Nature Challenge, a global effort to safely document and identify nature through the free and easy-to-use iNaturalist app. For the seventh consecutive year, Carnegie Museum of Natural History staff were among the participants taking on the challenge in and around the Pittsburgh region – and in 2024, the results were record-breaking! Totals for regional participants, identifiers, observations, and number of species hit their highest in the history of the challenge, thanks to a combination of warm, dry spring weather and dedication from participants. Observations and identifications made during the challenge are shared with scientists around the world, helping to both document and better understand the diversity of species around us.

Here are the totals from the Pittsburgh Region City Nature Challenge 2024 (CNC) – which are all records for this region’s participation!

Total participants who made observations: 643

Total participants who made identifications: 562

Total observations made: 10,050

Total species identified: 1,753

Total identifications: 16,875

Plants topped the list for observed species, with about 46% of the total, followed by insects with about 27% of the total. Other species identified but in smaller totals include fungi, birds, arachnids, mammals, reptiles, amphibians, and mollusks.

Mayapple (Podophyllum peltatum) took the top spot overall. This native plant species sprouts early in spring with long stems and umbrella-like leaves. The rest of the top 10 species are all plants, with the exception of the Red Admiral (Vanessa Atalanta), a beautiful butterfly with red bands on the wings. The most observed bird, the American Robin (Turdus migratorius),took spot 17, and at spot 26, the White-tailed Deer (Odocoileus virginianus) was the most observed mammal.

*The lovely Common Blue Violet (*Viola sororia) came in third place on the list of observed species.

With plants claiming nine of the top ten spots, it’s fitting to get perspective from the museum’s Section of Botany, who not only participate, but whose dedication puts them at the top of the list. Although they are literally professionals at looking for plants, the common message from the Botany staff is that anyone can do this challenge! The objective is to document nature all around us, from parks to neighborhood streets to city blocks and beyond.

Reflections from the Section of Botany Scientists

Curatorial Assistant Alyssa Landa made a point to visit similar spots that she visited last year, as well as around her yard and street to look at things she walks past every day. “CNC is a great reminder to check out places near me,” Alyssa said. “The big thing for me this year is just the number of new-to-me species I was able to log, just by taking that little bit of extra time to pay attention to what’s around that I might not otherwise be drawn to or notice! This time of year is always really exciting to me, and CNC is a fun reminder that there’s still so much to learn. It’s also a reminder to revisit my old, well-known (plant) friends too.” And her efforts made a difference! Alyssa logged the second highest total identifications, putting her expertise to excellent use.

A steadfast champion for the City Nature Challenge, Associate Curator of Botany Mason Heberling uses the challenge to check out the woods nearby where he lives. “I get caught up in other things and forget to appreciate the hyper-local diversity, within walking distance,” Mason said. “I make it a point to visit the same woods by my house every CNC.” Despite travelling out of the area for much of the challenge, Mason logged nearly 100 local observations!

And then there’s Bonnie Isaac, the section’s Collection Manager. Although City Nature Challenge is not a competition, it’s worth noting and applauding Bonnie’s efforts – she logged the highest number of both observations and identifications in the Pittsburgh region this year! She made 607 observations, which totaled 343 different species, and identified a whopping 1,697 entries! Bonnie shared her reflections about the challenge and described why it’s so important to her.

“When I was young, I could not spend enough time outdoors. I was outside from sunup till sundown or until my folks came looking for me. My curiosity led me to want to know what everything I encountered was. One year one of my sisters gave me a Peterson field guide for Christmas. This led me to discover that there was a whole series of Peterson field guides. Thus began my collecting career. I had to have every Peterson Field Guide that came out. (I now have a complete set of Peterson Field Guides, leather bound editions.) With these guides I could go out and try to identify everything I saw. I was in heaven. I am also a very competitive person. The City Nature Challenge takes what I love to do and makes it into a bit of a competition. I don’t live in the Pittsburgh City Nature Challenge region. I live in Lawrence County. During the pandemic the best I could do was help with identifying observations. Now that I can travel to the Pittsburgh region during the City Nature Challenge. Game on!” – Bonnie Isaac

Of Bonnie’s impressive collection of field guides, the first one she received was not plants, but animal tracks! It was written by Olaus J. Murie, a former employee of Carnegie Museum of Natural History who became a world famous biologist. Image credit: Bonnie Isaac.

For this year’s challenge, Bonnie visited Raccoon Creek State Park, Moraine State Park, Bradys Run Park, and Brush Creek Park. “The City Nature Challenge gives me a chance to get outside and see how many different things I can find,” Bonnie said. “Every year I challenge myself to find more species than I did the previous year. I also find identifying observations made by others somewhat satisfying. I get a chance to hone my identification skills and I get to see what others have found.”

Even for a botanist with decades of experience like Bonnie, each year brings surprises. “Every year there are surprises that I didn’t expect. I’ll discover that something is blooming that I didn’t think would be blooming yet, or I might find that someone found a plant growing in an area where I wouldn’t have expected it.”

*Bonnie has never seen an all-white Blue-eyed Mary (*Collinsia verna). She was excited to see that iNaturalist user “bquail” found some during the challenge. Image credit: © bquail via iNaturalist, CC BY-NC

Bonnie continued, “The top observations tend to be some of the same things, many plants that are not native to the area. It’s the things with only a couple observations that I find the most interesting. It’s these unusual observations that keep me eager to see what nifty things are being found basically in our own backyards. It also keeps me energized to get out and find more and to look closer for the minute details that might separate one species from another.”

The iNaturalist app also allows for recordings of bird song, frog calls, and other sounds. Bonnie connected with a user who identified a unique feature on one of her uploaded recordings. “One of the surprises for me was someone contacting me to let me know that one of my bird recordings had gray tree frogs singing in the background.”

*Bonnie’s favorite observation of 2024 was this Goldenseal, just coming into bloom. Image credit: Bonnie Isaac.*

A Global Effort with Big Results

City Nature Challenge 2024 was not just a success in Pittsburgh – globally the number of cities participating increased to 690 this year, a big jump from 482 cities in 2023! Here are a few of the worldwide stats:

Total participants: 83,528 in 690 cities in 51 countries

Total observations made: 2.4 million

Total species identified: 65,682

The big winner across the board, with most observations, species, and participants is La Paz, Bolivia!

The City Nature Challenge returns next spring. Let’s see if we can build on the truly remarkable success of 2024!

Jessica Romano is Museum Education Writer at Carnegie Museum of Natural History.

Slipper Snails Slide Between Sexes in Stacks

Or, Crepidula fornicata say, “Trans Rights!”

…if they don’t get eaten by their siblings first.

by Sabrina Spiher Robinson

*A pair of slipper snails seen from below. Image credit: Ecomare/Sytske Dijksen, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons*

A stack of Crepidula fornicata, grown together (with a little chiton, another type of mollusk, hanging out on the top of the family). — *A stack of* Crepidula fornicata, grown together (with a little chiton, another type of mollusk, hanging out on the top of the family). *Image credit: User Lamiot on fr.wikipedia, CC BY-SA 1.0 https://creativecommons.org/licenses/by-sa/1.0, via Wikimedia Commons*

Slipper snails, Crepidula fornicata, are a common find for shell collectors along the American east coast, and in some places on the west coast as well, where they have been accidentally introduced as an invasive species. But just because they’re common, doesn’t mean they’re not interesting – in fact, they’re one of the most well-studied marine snails, and all of that study has revealed a creature with a fascinating life cycle.

Crepidula are protandrous hermaphrodites – this means that all slipper snails begin their lives as male, and end their lives as female. As juveniles, they wander over the substrate, preferring hard surfaces like rocks, dock pilings, other shells, and even horseshoe crabs. But most C. fornicata will choose to settle on top of another C. fornicata, who might be settled atop another, and another, and so on. They live in stacks, sometimes of up to a dozen animals, one balancing on top of the next until their shells grow around each other, and they can no longer move, becoming sessile (stationary) by default.

Of course, a stack of all males won’t get very far reproductively. So, it’s time for at least a few C. fornicata to begin the next stage in their lives, and transition to females. Several things influence when the change takes place, primarily the animal’s size, because producing gametes is energetically costly: more sperm takes more energy than less sperm, and eggs take more energy than sperm altogether. But it’s not so straightforward as just growing to a certain size and changing sex. If there are no females around, for instance, some males will transition to females at smaller sizes than they usually would.¹ Alan Carillo-Boltodano and Rachel Collin write:

“In our experiment, pairs of snails (one small and one large) were kept in cups, either together or partitioned off with fine or coarse mesh, or partitioned, but switched from side to side to allow contact with the cup mate’s pedal mucus. The larger snails that were allowed contact with the smaller companions grew faster, and generally changed sex sooner, than did the larger snails in the barrier treatments, which allowed no physical contact. The smaller snails that were allowed contact with the larger cup mate delayed sex change compared to those separated from their cup mates … Our results suggest that the cue that affects size and time to sex change requires some kind of physical interaction that is lost when the snails are separated. Furthermore, contact with another snail’s pedal mucus does not compensate for the loss of physical contact.”²

In other words, when the slipper snails are in actual contact with each other, they seem to send signals to one another that help to coordinate growth and sex change.

In general, though, males will wait until they’re a certain size to transition, because larger males are more reproductively successful than smaller males, as determined by experiments that genetically test offspring to see whose genes were most successful in the stack. There’s one exception to this though – sneaky little guys! Male Crepidula inseminate females directly, so in general the male right on top of the female at the bottom of the stack will be the most successful fertilizer, and then the male on top of him, and then the others on top of them can’t reach and are out of luck for the moment. But! The smallest juvenile Crepidula, who have not yet chosen a stack of their own, have been found to sneak up on the substrate next to the female, inseminate her, and sneak away, using a strategy that gets around “bigger = more sperm.”³

Larger males might have more reproductive success than smaller males, but no one has more reproductive success than slipper snails who have transitioned to females. Eggs are a much bigger energy investment for an animal than sperm are, and so becoming a female requires a certain size to make the transition worthwhile. But once a slipper snail is female, she has a couple reproductive advantages: in the first place, she can hoard sperm for a long time, including her own from when she was a male, so she always has plenty of material to fertilize her eggs. This also means that while only a third or a quarter of the embryos will have a given male’s DNA, they’ll all have hers. Secondly, Crepidula females brood their young. Unlike many marine mollusks, who release their eggs and sperm into the water column where they meet and the embryo has to grow up among the plankton, at risk of becoming a meal for many things before they ever even get to grow into larvae, Crepidula keep their eggs in brooding pouches. Females keep between 15 and 20 pouches inside their shells, each containing between 50 and 450 embryos. She’ll brood them until they turn into larvae that can swim about on their own, keeping them safe to grow at least for a little while.

And thus, every Crepidula fornicata begins their life as a tiny, and sometimes sneaky, roaming male, sowing his wild oats; eventually he finds a nice stack to settle down on to become a dad; and then they transition sexes and live out her days as mother and base of the stack, brooding little babies in safety until they’re ready to hatch into larvae. Slipper snails make small stacks, but big happy families.

However, perhaps nowhere is safe. Once the eggs are brooding in their capsules, the mother slipper snail has no way to transfer additional nutrients or oxygen to the embryos. This environment of scarcity leads some species of Crepidula embryos to start cannibalizing each other! The embryos of Crepidula coquimbensis, a species of Crepidula first described in Chile, have at least been found to be choosy about eating their brothers and sisters. Brood capsules are fertilized by multiple males, meaning all the embryos have the same mother, but not every embryo has the same father. It was discovered that cannibalistic embryos were much more likely to eat their half-siblings than their full siblings, thus protecting embryos they shared a complete set of DNA with. It’s still not known how these embryos recognize kinship, though.⁴ In another species of Crepidula, Crepidula navicella, a gene in some of the embryos in each capsule switches on and arrests their development, basically turning them into meals for their siblings, a genetic predisposition to being either a cannibalizer or a cannibalizee.⁵

Of course, once the larvae are released into open water, all bets are off, and a lot of filter-feeding animals, including other mollusks, including other Crepidula, might eat them. However, Jan Pechenik reports:

“… in our study the same adults usually ingested their own larvae at much slower rates than predicted from the rates at which they cleared water of phytoplankton. These slower rates may in part reflect an inability or reluctance of adults to ingest particles of such large size … However, most of the larvae that we observed being entrained into adult feeding currents were ingested, and later appeared in feces, and adults were capable of ingesting larvae that were larger … Thus, lower than predicted rates of [larvae eating] by C. fornicata more likely reflect larval behavior – deliberate or not – reducing the likelihood of [getting drawn] into the adult feeding current, as suggested previously from studies with [other marine filter feeders].”⁶

At least baby Crepidula, once free, seem to have developed a way to avoid being eaten by their parents, if not their siblings!

Sabrina Spiher Robinson is Collection Assistant for the Section of Mollusks at Carnegie Museum of Natural History.

References:

[1] Proestou, Dina A., Goldsmith, Marian, Twombly, Sarah (2008) “Patterns of Male Reproductive Success in Crepidula fornicata Provide New Insight for Sex Allocation and Optimal Sex Change.” The Biological Bulletin (Lancaster), vol. 214, no. 2, 2008, pp. 194–202, https://doi.org/10.2307/25066676.

[2] Carrillo-Baltodano, Allan, and Collin, Rachel (2015). “Crepidula Slipper Limpets Alter Sex Change in Response to Physical Contact with Conspecifics.” The Biological Bulletin (Lancaster), vol. 229, no. 3, 2015, pp. 232–42, https://doi.org/10.1086/BBLv229n3p232.

[3] Broquet, Thomas, et al. “The Size Advantage Model of Sex Allocation in the Protandrous Sex-Changer Crepidula fornicata: Role of the Mating System, Sperm Storage, and Male Mobility.” The American Naturalist, vol. 186, no. 3, 2015, pp. 404–20, https://doi.org/10.1086/682361.

[4] Brante A, Fernández M, Viard F (2013) Non-Random Sibling Cannibalism in the Marine Gastropod Crepidula coquimbensis. PLoS ONE 8(6): e67050, doi:10.1371/journal.pone.0067050

[5] Lesoway, MP, Collin, R, Abouheif, E. (2017) “Early activation of MAPK and apoptosis in nutritive embryos of calyptraeid gastropods.” J. Exp. Zool. (Mol. Dev. Evol.) 328B: 449–461. doi:10.1002/jez.b.22745.

[6] Pechenik, Jan, Blanchard, Michel, Rotjan, Randi (2004) “Susceptibility of Larval Crepidula fornicata to Predation by Suspension-Feeding Adults.” Journal of Experimental Marine Biology and Ecology., vol. 306, no. 1, 2004, pp. 75–94, https://doi.org/10.1016/j.jembe.2004.01.004.

The Moon Snails Neverita duplicata and Euspira heros: Cannibal Predators of the Sea! … who also enjoy a nice algae salad

by Sabrina Spiher Robinson and Tim Pearce

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