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The Tufts Daily
Where you read it first | Friday, May 24, 2024

Dr. Jan Pechenik discusses intertidal animals and changing tides

The professor spoke about human activity’s effects on a selection of marine species and his work making scientific literature more comprehensible.


Crepidula fornicata, a species of sea snail is pictured.

Editor’s note: This interview has been edited for length and clarity.

Humans are tampering with the selective forces acting on organisms all over the planet and accelerating the rates at which selection is occurring. Dr. Jan Pechenik, professor emeritus of marine biology at Tufts University, suspects that one group of organisms is going to outlast many others: intertidal marine animals. They endure extreme fluctuations in their environment, particularly temperature changes, better than many others.

If you’re an intertidal animal like a barnacle, every day the tide comes in and out, and the environment changes dramatically. At high tide, in the winter you’re submerged underwater, but when the tide goes out, the temperature drops tremendously very quickly and might be well below freezing or even much higher than the seawater temperature. And then the tide comes back in and the temperature changes again, very quickly,” Pechenik said. “And yet, remarkably, nobody dies. Physiologically, intertidal organisms are capable of withstanding tremendous changes in the environment over a very short period of time. Intertidal animals endure a lot of physical stress — including daily exposure to air — year-round.”

Below, Pechenik joins me for a conversation on his research on intertidal organisms, exploring how stressors influence their lives after metamorphosis. We also discuss his writing about biology and his latest work translating Darwin’s seminal text, “On the Origin of Species,” into modern and accessible prose.  

Amelia Macapia: How did you get started writing “The Short Guide for Writing About Biology?”

Dr. Jan Pechenik: Many years ago, I was teaching a seminar course and was working with students on writing short papers. I was finding that students paraphrased what they were reading without setting up a convincing first paragraph to discuss the argument in the paper. I came up with this idea of having the students look at individual paragraphs, from a book like “Silent Spring” by Rachel Carson, and summarizing the main ideas in a single sentence that included all of the key features of the original paragraph and that could be understandable to someone who had never read that original paragraph. And so I was thinking, maybe I should write a guide to writing about biology.

AM: One of the things that really strikes me about Carson’s writing is how effortlessly she seems to delineate these findings to wide public audiences. There’s also a beautiful tension in her work between science and expression, and she seems to strike a wonderful balance between the two.

JP: It’s important to have people like her who understand things about various scientific fields and who can actually communicate those things in a very readable way to people who are not scientists. Hopefully, we’ll see more of those people writing for a more general audience in the future.

AM: I want to keep going on all this, but I also want to ask about the first marine organism you fell in love with; I’d like to anchor our conversation in that love of yours as well.

JP:  I worked on a number of organisms in graduate school; one of those species was a slipper shell snail, Crepidula fornicata. They’re stationary as adults, stack on top of each other and feed like oysters and clams by filtering single-celled algae — phytoplankton — out of the water. Every individual in that species starts off as a male, and as they get older each one turns into a female. If you put two males together, you always get a mated pair.

AM: Can you introduce your work on latent effects and explain what that term means?

JP: I do studies looking at the effects of larval experiences on how juveniles do. One very nice thing about working with C. fornicata is that I was able to rear the larvae and juveniles with very little mortality. So, what I was seeing in the juveniles or adults was not the result of selective mortality during larval development. If you see an unexpected impact of the larval stress on juveniles after metamorphosis, it is due to something that the larvae have experienced that has somehow carried over beyond metamorphosis. People (including me) used to think that metamorphosis was always a fresh start but it is not always. Sometimes you see the effects of non-lethal stress on larvae at a later point in development, even after they have metamorphosed. The juveniles in our studies were often less tolerant to various stresses if the larvae had been stressed sublethally and in some cases were more tolerant. So, predicting the impact of sublethal stresses experienced during larval life is not going to be very easy to do.

AM: With the metamorphosis of butterflies, there is this total liquidation of the body in the chrysalis stage, but somehow their DNA still retains the body plan to grow into a full organism, and this can be manipulated experimentally. Is that similar to what is going on with marine snails in their metamorphosis?

JP: Before metamorphosis the larval shells are very weakly calcified, so that they continue to be lightweight for swimming and they’re transparent. But after they metamorphose, the shells become much more heavily calcified, so the gene expression patterns shift. My suspicion is that some of these stresses that are experienced during larval development somehow change how certain genes are expressed after metamorphosis. The larvae survive and metamorphose, but the juveniles grow more slowly than the controls, and sometimes they don’t survive as well in adulthood. If they grow more slowly, in the field they are more vulnerable to predators and things like [dehydration]. A lot of organisms exhibit these kinds of latent effects, usually they are negative effects.

AM: What are the largest stressors causing negative impacts after metamorphosis?

JP: I’ve looked at the impacts of ocean acidification, temperature stress, salinity stress and heavy metal concentrations like copper and cadmium. If I were still doing these studies, I would start looking at the impact of microplastics. Plastic pollution is becoming an increasingly important negative in the marine environment, and deep sea animals even have microplastics in their tissues.

AM: One of the things that I was most struck by when I was in class with you was these multiple orders of sensory processing in invertebrates and this incredible sensitivity to the environment. I remember learning about the nematocyst-laden tentacles of anemones, for instance, that are able to detect whether other anemones around them are part of the same species or whether they pose a competitive threat, and that they can shoot these spears out on cables to fight for the space they are living on. How do you see the debate on whether invertebrates are conscious?

JP: I’ve done a number of studies with hermit crabs. It turns out that hermit crabs are very careful about the shells that they pick to live in, and they pick shells that are exactly the right size for them. If the shells are too large, they’re going to be too heavy to carry around. If they're too small, the crabs are not going to be able to withdraw into them if a predator attacks them. They're also really good at assessing various parts of the shell for damage and damage is something they avoid to a great extent. I don’t know what they are thinking but certainly they make very careful choices about the shells they pick to live in. I've done a lot of studies also looking at what the effects of various stressors on their ability to actually choose the most protective shells are, so I think in some way they have to be sentient beings. Whether they’re thinking or not, I don’t know. With snails and clams and oysters, I don’t think that they're all that cogent, but the larval stages are very active and they can respond to things like light and sometimes sound. Whether it’s just an automatic processing, or whether they’re actually making decisions, I don’t know.

AM: I was reading a book by Peter Godfrey Smith called “Other Minds,” and it’s about cephalopod intelligence and how that has evolved a number of times throughout genetic history. In terms of evolutionary history, they are linked together with all of these other invertebrates and it’s so interesting, this debate about whether one thing is less conscious than another.

JP: Yes indeed, cephalopods are in the same phylum with clams and snails. Their brains are incredibly large and they learn things quickly and their behaviors are very complex. There probably are some invertebrates like hermit crabs and octopus that think in ways that must be least similar to the way our cats and dogs process information. We are in the same phylum as sea squirts, by the way; it just shows the incredible ability of evolution to cause offspring to branch off in such amazing directions.

AM: It seems that a lot of your work is dedicated to translating the thrill of scientific questioning across human history and culture and its relevance for all of us. How did you go from writing about marine biology to writing about evolutionary biology?

JP: When I was an undergraduate at Duke [University], I took a psychology course, and the instructor for that course assigned the first couple chapters of “On the Origin of Species” — I never read the rest of it. At some point in my career I thought “Hey, I’m an ecologist and I work on behavior and physiology too,” and I thought I need to read this. It’s such an important book. It transformed our understanding of life and how things work, explaining the diversity of life on our planet and also how the changes that humans are having on the selective forces are going to bear out.

Very few of my colleagues have ever read “On the Origin of Species.” Some of them started it, got halfway through the first chapter and then gave up because of his writing. His sentences are long and his verbs are very weak. He throws lots of names around and doesn't tell you who those people are. So, my book has a lot of footnotes. I tightened up the writing so the verbs are much stronger. I explain things more clearly, but all the ideas are still Darwin’s. I often say that what I did was translate Darwin’s book into readable English.

It’s interesting because when he was in college, his father wrote him a letter and told him: “You’re going to be an embarrassment to the entire family.” Darwin was going to go into the ministry, be a clergyman and collect animals as a hobby and almost by accident got invited to go out on the Beagle with Captain FitzRoy. After a couple of years, Darwin’s life changed completely. He started noticing things from island to island and place to place where they stopped. That got him thinking about how animal species are distributed around the world and why things on islands were often different species but similar to what was on the mainland. And he came up with this amazing idea of evolution.

AM: We’re dealing with this paradigm shift from what was perceived as the slow and deliberate piece of nature, with natural selection to the acceleration of environmental degradation and these rapid interlocking, ecological catastrophes. Some scholars have argued that we’re overriding evolution. And then others have argued that it's happening faster than ever. What are the new evolutionary models that we're looking at? And do you think this is the end of Darwinism?

JP: Darwin understood — from looking at fossil preservations — that many species eventually went extinct. He didn’t understand mass extinctions or genes but realized that certain traits got selected generation after generation. This is because individuals with those particular characteristics had a better chance of surviving and a better chance of reproductive success. If those offspring had those traits, then over long, long periods of time, those traits would become more and more common in the population. Then, the organisms could turn into a new species whereas the individuals that didn’t have those traits might slowly go extinct.

One of the problems we’re facing now is that our environments are changing so quickly in so many ways. Organisms don’t evolve with deliberate intent. Certain mutations pop up by random accident. The species evolves, but it’s a very slow process over generations and generations. The rate at which our environment is changing now is really fast, and whether organisms will have enough time to have these random successful mutations popping up and getting transferred to future generations before the populations go extinct is not clear.

The selective forces that are acting on organisms on the planet now are just really different from what organisms have experienced in previous centuries. I think things that reproduce more quickly at younger ages are maybe more likely to survive than the species that take decades, or even years, to become sexually mature and then produce very few offspring. Selection is going on, but it’s now human-induced selection; it’s not just natural selection. Predicting the impact of such latent effects on marine fisheries and marine mammals will be very difficult, since marine food webs are so complex. But documenting that impact in the coming years will certainly be interesting.