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Does Environmental Change Jog the Memory of Conditioned Scallops?

June 09, 2023

Investigating whether scallops’ memory-like responses can help them adapt to climate change.

A hand holds three greenish gray bay scallop shells.

Life is adaptable. We have all overcome challenges and experienced moments of resilience along our human journey.

Even the smallest building blocks of life, cells, overcome challenges and build resilience, but how do they do this? Our team is working to answer this very question.

I am a postdoc at the NOAA Fisheries Milford Laboratory. I am captivated by the mechanisms invertebrates—animals without a backbone—use to persist on our ever-changing planet. Especially intriguing are “memory”-like responses.

Two tanks side by side, each with seawater and more than ten scallops. The tank on the left has a small red label that reads “PH 7” and the tank on the right has a green label that reads “PH 8”.
Adult scallops were tagged to track the different ocean acidification histories they were raised in before being placed in tanks with either the same or different levels of CO2. Notice that each color tag is represented within the single green labeled tank – these represent animals of all ocean acidification histories exposed to the ‘low’ ocean acidification level. Credit: NOAA Fisheries/Katherine McFarland

What this means in a nutshell: previous experiences, whether challenging or not, can affect how animals respond to change. Scientists commonly study animals with short generation times (fruit flies or mice for example) so that they can repeat experiments and advance research for human health. Findings have upheld the phrase “what doesn’t kill you makes you stronger,” suggesting a benefit of prior experience to cope with a challenge faced later in life. It is possible that this framework can also help us improve climate resilience for shellfish.

Our team is completing a large 3-year study investigating how bay scallops adapt over three generations of exposure to ocean acidification. It’s an ambitious yet achievable feat because this species can reach adulthood in less than 1 year! Ocean acidification is a change in seawater chemistry intensified by global carbon dioxide emissions. Animals that build shelled structures, such as scallops, are particularly susceptible to these changes in their environment. Do I smell an experiment brewing!?

My study is a “study within a study”, looking at three populations from the second generation of bay scallops that are part of the larger multigenerational experiment. We raised each population under either low, moderate, or severe ocean acidification conditions for their entire lifetime (continuously for 10 months!). In this case, “low” was classified as current-day levels and “moderate” as the anticipated condition for the global ocean by 2100. Since ocean acidification is projected to intensify within coastal regions where bay scallops live, a “severe” level was chosen to represent a future extreme.

Conditioned under three levels from embryos until adulthood, their differing histories set the stage. Then each group of adult scallops was rearranged for a short exposure to all three ocean acidification levels. This allowed us to test the “memory” of the three bay scallop groups. How does ocean acidification affect the cell? Does prior experience play a role?

Dubbed the powerhouse of the cell, mitochondria are essential for cellular energy production and were key to this experiment. Healthy mitochondria represent healthy, resilient cells. We wanted to know how the scallops’ mitochondria varied with the level of ocean acidification at which they were raised in and subsequently exposed to as adults.

To measure them, we extracted hemolymph (the blood of invertebrates) from dozens of scallops. Then, we dyed live cells and measured mitochondrial status using fluorescence flow cytometry. A flow cytometer is a laser-based instrument that measures the light emitted from single cells or particles. We used fluorescent dyes, or “probes,” that bind to traits in hemolymph cells to shed light upon their status.

Four images: The top left image shows many researchers preparing to extract hemolymph, the blood of the bay scallops, in a laboratory setting. The top right shows two gloved hands using a syringe to extract hemolymph from a bay scallop. The bottom left shows a gloved female scientist dissecting a bay scallop on a tray. The bottom right shows a gloved female scientist putting a sample of cells from a bay scallop in a flow cytometer. A computer screen with graphs is visible in the background.
Our project was a team effort. Each sampling timepoint included hemolymph extractions (top right), gill and adductor muscle tissue dissections (bottom left), gonad assessments, and analysis of live cells (bottom right) – all within a single day! Credit: NOAA Fisheries/Katherine McFarland

Bay scallops raised under moderate and severe ocean acidification had fewer live cells. But, their cells had more robust mitochondria compared to scallops raised under low acidification conditions. This is evidence that history does play a role: the cells that had more healthy mitochondria seemed to acquire a new strategy built from prior experience.

We have not determined whether this trait better prepares the scallops to respond to environmental change. More insights will be gathered from preserved gill tissues we collected from the same individuals. As this project continues, we anticipate learning more about cellular memory and resilience from scallop’s genes!

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