Carnegie Museum of Natural History

One of the Four Carnegie Museums of Pittsburgh

Tim Pearce

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Speculation: Glowing Snails and Jumping Genes

By Tim Pearce

Only one species of land snail is known to glow in the dark: Quantula striata, albeit very faintly. A glow organ under its chin produces yellow-green light, and the rest of the body glows very faintly. The snail occurs in some areas of Southeast Asia including Malaysia and Singapore. The snail uses the same system to glow as fireflies, two chemicals: luciferase reacts with luciferin to produce light.

Scientific papers, including those by Yata Haneda, have characterized the wavelength of the light, the interval of the flashes, which part of the body glows, and differences in glowing between juvenile and adult snails. However, none of the papers has addressed why the snails glow. Given that light production is energetically costly, there must be some evolutionary advantage to glowing. How does glowing help the snail in its daily life?

There are five known reasons that organisms glow: (1) attract mates (as in fireflies [originally for larval defense, see Branham and Wenzel 2003, Cladistics, 19:1-22]), (2) attract prey (as lures in deep sea fish), (3) attract dispersers (insects attracted to light disperse spores from glowing mushrooms), (4) escape predators (deep sea octopus create glowing clouds and slink away unnoticed), (5) burglar alarm (some ocean microorganisms glow when copepods try to eat them; the glow attracts fish that then eat the copepods).

I speculate that Quantula striata glows to escape predators.

Quantula striata, land snail that glows in the dark
Quantula striata, the only species of land snail known to glow in the dark.

Larval fireflies eat land snails and larval fireflies occur in Southeast Asia where this glow snail lives. Perhaps a glowing snail could fool a hungry firefly larva by falsely conveying that the snail is already occupied, so glowing might ward off an attack by a firefly larva. Thus, the evolutionary advantage is that glowing snails might experience less predation.

One way to test this hypothesis would be to expose glowing and non-glowing snails to larval fireflies to determine which kind of snail gets eaten more. I haven’t tried this experiment yet, because I don’t have glow snails available in my lab.

More speculation: could the genes for the light-producing system have moved from a firefly to this snail? It is a remarkable coincidence that the snail and the fireflies both produce light using the luciferin and luciferase system. What are the chances of that! One possibility is that the genes to produce luciferin and luciferase were somehow transferred from a firefly to an ancestor of the snail, then spread over time throughout the species. While such horizontal gene transfer is thought to be relatively rare, the transfer of genes from one species to another is known in single celled organisms (e.g., the spread of antibiotic resistance among bacteria species), and evidence exists that it has occurred in some multi-cellular organisms.

One way to test whether horizontal gene transfer could explain the luciferin and luciferase lighting system in Quantula striata would be to sequence the DNA of the snail and the DNA of fireflies living in Southeast Asia. If both genes for luciferin and luciferase were transferred from the firefly to the snail, there is a good chance that additional DNA on either side of those two genes was transferred as well. If additional firefly DNA exists near the luciferin and luciferase genes in the snail, that would be strong evidence that the snail’s ability to glow came from a firefly.

It could have happened!

Relevant Snail Joke: 

Q: What happened to the glow-snail that lost its glowing organ?

A: It was de-lighted.

Timothy A. Pearce, PhD, is the head of the mollusks section at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Land snails in Mt Lebanon: BioBlitz confirms rare species and finds two additional gastropod species in urban parks

Tim Pearce (Curator of Collections, Mollusks) surveyed land snails in a BioBlitz organized this past weekend by the Mt. Lebanon Nature Conservancy at Robb Hollow Park in Mt. Lebanon. Other members of Carnegie Museum of Natural History who participated in the BioBlitz were Bonnie and Joe Isaac (Collection Manager and volunteer, respectively, Botany).

Pearce targeted five locations in Robb Hollow Park and found 10 species of gastropods, including a rare species, and two species that had not been found in Mt. Lebanon during previous BioBlitzes in 2003 and 2005 at Bird Park and Twin Hills Park. The two new records were the introduced slug Arion intermedius (common name: Hedgehog Arion) and a minute native snail, Columella simplex (High-spire Column).

BioBlitz participants picking minute snails from a leaf litter sample.
Duquesne University students Josie (left) and Dannielle (right) picking minute snails from a leaf litter sample during the BioBlitz.

 

The most exciting snail find is the rare snail, Glyphyalinia raderi (Maryland Glyph), living in Robb Hollow Park. This native species has been found in Pennsylvania only 18 times previously, in six counties in the southwestern part of the state. Most of the localities are associated with limestone in undisturbed natural areas, so the finding of this snail in Robb Hollow Park this year and in Twin Hills Park in 2005 are big surprises. Why is a rare snail living in these non-pristine urban parks? Furthermore, it is almost never found alive, but the two individuals seen in Robb Hollow park were both alive.

Ten species is a bit on the low side for a snail survey, but is better than Pearce expected. When he collected the samples, he noticed that (non-native) earthworms had consumed most of the duff layer of dead leaves, leaving very little food and living space for snails, so he initially didn’t have high hopes for finding many species. But he found ten, and happily, most of the snail species are native. “In urban settings, I often find a large proportion of introduced species, usually from Europe,” said Pearce. “But in Robb Hollow Park, seven of the ten species are native, which is a pretty good proportion.”

Timothy A. Pearce, PhD, is the head of the mollusks section at Carnegie Museum of Natural History.

Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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From Nebraska or Bust, a Truck load of Mollusks

By Tim Pearce, Curator of Collections, Section of Mollusks

A rare opportunity for Carnegie Museum of Natural History occurred in early May when we adopted an extensive mollusk collection.  Although the mollusk specimens had been well cared for, their existence at the Nebraska State Museum, University of Nebraska, was little known to mollusk researchers over the past 100 years, so they were seldom used. The curator recognized that for the foreseeable future, the museum will have priorities other than mollusks, so would not have resources to properly work up the collection. I was very excited when he contacted me about the possibility of transferring the collection to Carnegie Museum. At Carnegie Museum, we have the expertise to identify, update names, catalog, and make the information available on the internet, so it will be available to researchers around the world.

The collection has an excellent collection of freshwater mussels. Carnegie Museum had four lots of freshwater mussels from Nebraska, now we have more than 158 lots. Also included are many marine and terrestrial mollusks from pre-Castro Cuba, and most of the collection is pre-1929.

Carefully packing the collection into 60 boxes took two of us seven days. We are very grateful to the kindness and generosity of the museum director and curator for lodging us and providing access to the collection, even over the weekend.

We drove the collection to Pittsburgh in a rental truck. Given that I consider each shell to be as valuable as a Picasso, every time we hit a bump, I thought, “Oh, my poor Picassos.”

As we drove, we recalled the odd black leather case about 2 by 3.5 inches in size that we came across tucked away at the back of a drawer in the mollusk collection. Inside the case, we found a shell, a cone shell to be exact, and a small carefully folded paper wedged beside the shell. The unfolded paper was a letter dated July 23, 1938, which read, “Sirs, 30 years ago I stole this shell. Have had pecks of bad luck. Am returning the shell and hope the bad luck will end.” The letter was signed with the man’s first and last name, and his address.

What was going on in his life in 1908 that prompted him to steal the shell? When did he make the connection between the theft of the shell and bad luck (that comes in pecks)? Did his luck improve after the return of the shell? We can only wonder.

The shell and the intriguing letter in their case continue to reside with the museum in Nebraska as part of the historical record; I consider it to be a priceless artifact.

Timothy A. Pearce, PhD, is the head of the mollusks section at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Ask a Scientist: What is the fastest snail?

Assistant Curator and Malacologist Dr. Timothy Pearce weighs in on which snail or slug is the fastest of them all. The answer may surprise you!

 

Ask a Scientist is a new short video series where we ask our research staff questions about the millions of amazing objects and specimens stored in our collection. Tune in on YouTube, and submit your own questions via Twitter @CarnegieMNH.

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(Not So) Boring Clams

by Tim Pearce

Some clams, in the families Teredinidae and Pholadidae, bore holes in wood or rock that is immersed in seawater. We humans often think of wood and stone structures as relatively permanent, but these clams force us to challenge that idea. In fact, the wood-boring clams, known as ship worms, are a centuries-old scourge to shipping activities because they weaken wooden ships and pilings.

peice of wood covered in long thin holes
Wood bored by shipworm, Lyrodus pedicellatus

The wood-boring clams are highly modified from the clams that normally come to mind. Their shells are reduced to a pair of abrasive cutting tools at the end of a long, worm-like body. The clam twists the shells back and forth, breaking off chunks of wood as it burrows through the wood. The clam eats the wood, aided by symbiotic bacteria that digest the wood. As the clams burrow, they somehow seem to know when they are near another clam’s tunnel and they avoid breaking into it, but how they know is a puzzle.

grey rock with holes, clam shells can be seen filling some of the holes
Rock bored by clam, Penitella penita, from Washington State

Human efforts to prevent shipworms from destroying wooden ships and pilings included coatings containing tributyl tin (TBT). While paints containing TBT did protect against shipworm damage, the chemical was toxic and caused reproductive problems in aquatic organisms. In particular, TBT causes masculinization of female fish, snails, and other aquatic species. So, other methods to protect wood are now used instead.

Rock-boring clams also have shells adapted for abrasion at one end, but they differ from the ship worms because the shells of the rock-boring clams are not as reduced as in the ship worms, and the rock boring clams do not derive nutrition from the rock particles. As the clams bore into the rock, they grow, so the burrow tapers wider inward, so the clam shell cannot get out. However, the clam gains great protection from predators. The clam siphons protrude through the rock opening to bring in water and food and to expel wastes.

white clam shell
Rock-boring clam, Zirfaea crispata, from England

Other clams specialize in boring in calcium carbonate. These clams are important in the destruction of limestone, reefs made of coral skeletons, and even shells of other mollusks.

Timothy Pearce is the Head of the Section of Mollusks at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Section of Mollusks Tours

Tim Pearce holding up a shell from the hidden collection

Did you know that the Section of Mollusks Assistant Curator Tim Pearce has been conducting monthly behind-the-scenes tours for the public since 2007?

On these tours, participants often learn for the first time that the museum has huge collections and scientists who conduct
research, and they see crowd pleasers such as the killer sea snail, the giant clam, and they look through the shell to see the beating heart of a live land snail.

Check our Section of Mollusks for tour times!