Do Light and Darkness Shape the Patterns on Shells? A Grass Fellow Investigates

Two zebra nerite snails: One with pattern shift from before arriving at the MBL's Grass Lab (left) and one that experienced damage in the past, but continued with its original diagonal stripes (right). Credit: Kyra Schapiro

Kyra Schapiro knows how to find a good shell. A self-professed sheller 91บฃฝวยายื“ 91บฃฝวยายืœ Yes, it91บฃฝวยายื™s a noun,91บฃฝวยายื she said 91บฃฝวยายื“ Schapiro has amassed hundreds of seashells. 91บฃฝวยายืœIt91บฃฝวยายื™s the patterns and the beauty91บฃฝวยายื that compels her to shell, she explained. And even at a young age, she could 91บฃฝวยายืœrespect that something was making this [shell pattern] with some sort of plan or intention.91บฃฝวยายื 

From her hours of searching the surf of Hillsboro Beach, Florida, Schapiro couldn91บฃฝวยายื™t ignore certain patterns repeating on each shell she saw. Like the Fibonacci sequence --  mathematical spirals seen in nature, from hurricanes to flower petals -- how do these patterns emerge? What mechanisms has nature evolved to design these displays, and what determines one shell91บฃฝวยายื™s subtle differences from another? 

Statue of shells and sea glass from beach excursions
Figurine created by Kyra Schapiro from shell, glass, and beach fragments she collected. Credit: Meghan Willcoxon

 

These questions bubbled in the background while Schapiro trained as a neuroscientist at the University of Pennsylvania and searched for patterns in cognition and working memory. After yet another painstaking attempt to record single-neuron activity in monkeys, she sought solace in shells 91บฃฝวยายื“ this time, as a scientist.91บฃฝวยายืฏ

Pattern switch 

As a 2025 at MBL and postdoctoral scientist at , Schapiro has taken to a different type of shelling. For the first time, she91บฃฝวยายื™s collecting shells with their living occupant: the zebra nerite snail.  She houses dozens of snails in experimental tanks and tracks how their patterns grow and change under different conditions.91บฃฝวยายืฏ&ฒิฒ๚ฒ๕ฑ่;

Zebra snails have the right kind of shell pattern to study. They have diagonal bands, so pigment stripes the shell in a different direction from the shell91บฃฝวยายื™s growth. Under normal conditions, the biology follows a blueprint, painting a continuous design of dark and light stripes.91บฃฝวยายืฏ&ฒิฒ๚ฒ๕ฑ่;

But when something changes in the environment 91บฃฝวยายื“ access to light, perhaps 91บฃฝวยายื“ the diagonal striping stops, leading to a dramatic pattern change, Schapiro said. Instead of resuming the original pattern, they switch to a new design, laying down pigment according to a different template. 91บฃฝวยายืœMy basic theory is that they are somehow sensing where in the pattern they left off,91บฃฝวยายื using the new template to guide their future stripes, Schapiro said 

Schapiro has six collection tanks: one control and five with unique manipulations. She aims to see which conditions disrupt shell pattern formation.91บฃฝวยายืฏ&ฒิฒ๚ฒ๕ฑ่;

In a light tank, zebra snails experience constant brightness, while the algae blooms flourish. In a nearby dark tank, snails experience the opposite, with 24-hour midnight waters. Schapiro hypothesizes that information from light triggers which band (light or dark) gets laid down next. Under normal lighting conditions, the light and dark stripes alternate. But if an input, such as light, is shut off, the snail will only produce dark bands.91บฃฝวยายืฏ&ฒิฒ๚ฒ๕ฑ่;

A few snails developed a pattern change prior to arriving at the Grass Lab in May, boosting support for Schapiro91บฃฝวยายื™s hypothesis. Perhaps the days spent in dark shipping containers extended the dark stripes.91บฃฝวยายืฏ&ฒิฒ๚ฒ๕ฑ่;

She also has three wallpapered tanks: plain white, striped, and checkered. 91บฃฝวยายืœIf I put them in an environment where they no longer blend in, but rather stand out, can they adapt?91บฃฝวยายื Will the snails change the direction of the stripes, she wonders, in response to a different background? These are questions informed by evolution, which implies some shell pattern will best equip a snail for its environment.91บฃฝวยายืฏ&ฒิฒ๚ฒ๕ฑ่;

Tapping into the (neural) network 

In addition to weeks of behavioral observation, Schapiro will probe the organism91บฃฝวยายื™s nervous system, looking for a neural response to light. But a snail91บฃฝวยายื™s physiology makes it difficult to electrically record from the nerves. 91บฃฝวยายืœSnail nerves are deeply embedded, and the tissue is thin,91บฃฝวยายื Schapiro said.91บฃฝวยายืฏ&ฒิฒ๚ฒ๕ฑ่;

But one of the benefits of being at the MBL, Schapiro said, is access to resources and expertise to experiment with different methods.  

91บฃฝวยายืœThere are so many people who know different things91บฃฝวยายืฆI can just wander around and ask, 91บฃฝวยายื˜What methods do you use? Can you tell me about this? Am I doing this right?91บฃฝวยายื™91บฃฝวยายื 

This has allowed her to pick up a peculiarity between the local species of snail, Crepidula fornicata, and her experimental zebra nerites, Vittina turrita.91บฃฝวยายืฏ&ฒิฒ๚ฒ๕ฑ่;

slipper snail, a local species in Woods Hole, Massachusetts
Crepidula fornicata, or the "slipper snail," is a species local to Woods Hole and Schapiro's control organism. Credit: E.A. Lazo-Wasem

 

In probing their neural networks, Schapiro has found that V.  turrita has many more branches than C. fornicata, which seem to have more of a 91บฃฝวยายื˜net91บฃฝวยายื™. She wonders if there91บฃฝวยายื™s a connection between the number of branches and the number of stripes on the shell. If there is, that would strongly indicate a neural basis for pattern formation. 

If neuroscience underlies pattern change, then Schapiro has tapped into something in ways that haven91บฃฝวยายื™t been explored before. Perhaps snails are neurologically primed to create their own designs, patterned by whatever environment they experience.91บฃฝวยายืฏ&ฒิฒ๚ฒ๕ฑ่;