Thoughts of a clam

To us active, dynamic mammals, the humble clam can appear positively…inanimate. Their nervous system is decentralized relative to ours, lacking any sort of brain, and to the untrained eye, it can appear that their only discernible reaction to the outside world is opening or closing. Open = happy, closed = not happy; end of story, right? Some vegans even argue that the clams are so nonsentient that it is okay to eat them and think of them as having no more agency than a vegetable!

You might already have predicted I intend to tell you about just how animate and sentient clams can be. But let’s start out by describing the nuts and bolts of their nervous system. As with many invertebrates, their nervous system is distributed throughout their body as a system of ganglia. Ganglia are clumps of nerve cells which may have local specialization, and transmit messages within neurons using electrical potentials. At the connection between cells (called a synapse), neurotransmitters are used to pass signals to the next cell. Researchers have found that bivalves use “histamine‐, octopamine‐, gamma‐aminobutyric acid‐ (GABA)…like immunoreactivity” in their central and peripheral nervous systems, much like us vertebrates do, and other studies have even found that the response to serotonin and dopamine is localized in nervous tissue linked to different organ systems.

Nerve cells (bright green) highlighted in a larval oyster with fluorescent dye (from Yurchenko et al 2018)

These systems of chemical nerve transmission are truly ancient, likely dating back to the formation of complex animal body plans in the earliest Cambrian. Researchers have great interest in studying these nervous and hormonal signaling systems in mollusks because they can shed light on the relative flexibility and limitations of these systems throughout the animal tree of life. Characterizing these systems can also allow us to understand the mechanisms that bivalves and other animals use to react to environmental stimuli.

Electron microscope view of gill cilia, zoomed in 1000x (from Dan Hornbach)

Like humans, bivalves spend a lot of time and effort eating. Most bivalves eat by filtering food from passing water with tiny cilia on their gills. These cilia work to capture food particles and also act as a miniature rowing team moving water along the gill surface. The bivalve needs a way to control this ciliar activity, and researchers found they could directly control the speed at which oysters move their cilia by dosing them with serotonin and dopamine, which respectively increased and decreased activity.

Bivalves also work very hard to make babies. Most bivalves reproduce by releasing sperm and eggs to fertilize externally in the water column. To maximize their chances to find a mate, they typically save up their reproductive cells in gonads for multiple months and release them in a coordinated mass spawning event. It appears that this process is controlled by hormonal releases of dopamine and serotonin. Researchers have determined that serotonin concentrations vary through the year, with mussels in New England using it to regulate a seasonal cycle of feeding in summer, followed storing of that energy for winter. During the winter when food is less available, they use that stored energy to bulk up their gonads in time for reproductive release in spring months, when their larvae have plentiful access to food and oxygen, ensuring them the best chance of survival. In recent decades, aquaculturists have learned to use serotonin injections to induce spawning in cultured clams, to ensure they will have a harvest ready at a certain time of year.

So bivalves are very sensitive to the seasons. How about shorter term sources of excitement? You might have observed this yourself through the clam’s most iconic activity: opening and closing its shell. Clams close their shells with powerful adductor muscles which pull the two valves together. A springy ligament at the hinge pulls the shell open when the muscles relax. Just like us, the clam needs to use nerve cells to signal the muscle to do its thing. In addition, two different sets of ganglia act to control the foot that some bivalves can extend to dig into sand, with one ganglion acting to extend the foot and the other causing it to contract. While clams don’t have a centralized brain with specialized regions for different uses like we have, this represents a sort of specialization of neural systems with a similar result.

Clam licking salt - Imgur
This iconic gif is often shared along with the claim it shows a clam “licking” salt. It is actually using its foot to search for a place to dig. The salt was not needed.

When a certain neuron is used repeatedly, it can form a cellular memory allowing the organism to acclamate (ugh sorry) and moderate its response to a particular stimulus over time. Giant clams, for example, close their shells when their simple eyes detect a shadow overhead. This behavior can protect them from predation. When I conducted some of my PhD research, sampling body fluid of aquarium and wild giant clams with a syringe, I noticed that captive clams didn’t close up in response to my shadow overhead, while wild clams required me to sneak up and wedge their shells open with a wooden block to do my work. I suspected that after exposure to frequent feedings and water changes by aquarists, the clam had “learned” that there was no reason to expend energy closing its shell. Meanwhile, in the process of proving that our sampling technique was not harmful to the animal, I discovered that clams which detected my shadow would quickly reopen within seconds when I hid from them, while those that were stuck by a syringe would stay closed for minutes before opening and beginning to feed again. Makes sense!

Other researchers noticed this phenomenon as well. One group found that giant clams repeatedly exposed to shadows of different sizes, shell tapping and even directly touching its soft tissue began to habituate (become accustomed) to the stress, opening more quickly and staying open longer each time the stimulus occurred. Even more interestingly, they did not transfer that habituation between stress types; for example, the clams that saw a shadow again and again would still react strongly to a different stress like tapping its shell. This suggests the animal can distinguish between different threats along a spectrum of seriousness, with touching of tissue (similar to a fish pecking at its flesh) being the most serious threat with the most dramatic response.

Another study determined that larger giant clams stayed closed longer than smaller ones in response to the same threat. They proposed this was related to the greater risk large clams face as they have more tissue area vulnerable to attack. While the clams might not have made a “conscious” decision in the way we do as thinking creatures, they were able to place their individual risk in context and vary their response. This ability to tailor a response to different risk levels is a sign of surprisingly complex neurology at work.

Inside the Scallop
Close up of the eyes of a scallop. Each is a tiny crystalline parabolic mirror (photo by Matthew Krummins on Wikipedia)

Scallops show some of the most complex bivalve behaviors. This relates back to their unique adaptations, including simple eyes that can resolve shapes and the ability to swim away from danger. Scallops have been found to discern between predator types by sight alone, to the extent that they did not initially recognize an invasive new predatory seastar as a threat. When swimming, they are capable of using this vision to navigate to places where they can hide, such as seagrass beds. It would be very interesting to compare the behavior of scallops in marine protected areas to those that can be freely harvested. Do they vary their behavior in response?

I hope I’ve made clear that while clams are not exactly intellectual powerhouses, their behavior is much more complicated than simply sucking up water and opening or closing their shells. Like us, they inhabit a complex environment that requires a multitude of responses. Their nervous systems have evolved to allow them to survive and adopt nuanced behaviors which they can vary on the fly, and which us “higher” animals are only just beginning to comprehend.

Israel: Field Report!

So I’ve been living in Israel since the start of November after a whirlwind of defending my PhD, moving out of Santa Cruz forever and suddenly moving to another continent for a postdoc. I’ve been working on clams, taking samples, using an SEM and planning a new manuscript, but I have also been learning a lot about living in a country that is at once strangely familiar and completely foreign. I’m coming back to California tomorrow for a Holiday break, so I took an hour to reflect on what I’ve learned about this country so far. Here are some random things I’ve learned about Israel during my time here.

Israel is small


Israel is a tiny country by my Californian standards. You can take a bus along the entire length of it in less than seven hours. I am in Haifa on the farthest northern part of the Mediterranean coast, but in 2016, I lived down in Eilat for two months. Despite its small size, Israel has a variable climate depending on where you are. Up in Haifa, they have have a classic Mediterranean climate which reminds me of California in a lot of ways (think chaparral and coastal dunes, though a little more humid than I’m used to and with more thunderstorms). The Negev desert is in the South, which is intensely dry, hot and sometimes completely devoid of vegetation.

Happy naturalists!

For birders, I’ve noticed the North is dominated by hooded crows from Europe while the South is dominated by house crows, an Asian species. In general, because they’re at the nexus between Europe, Asia and Africa and the gradient between those ecoregions, Israel and the Middle East overall are very biodiverse. As a result, there is a vibrant culture of naturalists in this country who want to know about every aspect of every species. When I post something to my iNaturalist, within a few hours someone who is an expert on that taxon confirms or corrects me, without fail.

Delicious food+drink

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Living here, I have been subsisting of a diet based largely on hummus, falafel, shawerma, tahini (try the dark kind!) and pita, with plenty of veggies thrown in. In fact, there are restaurants where they just serve you a bowl of hummus with pita and you have at it. Be prepared for the food coma. For beers, I guess Danish beer companies got a big foothold here early on because the defaults are Carlsberg, Tuborg, Heineken etc. The biggest native Israeli brewery is Gold Star, and they’re not bad! And there are a growing number of Israeli craft breweries. Overall I approve, though they sometimes experiment a bit too much and taste odd, and a lot of them don’t really seem to know what an IPA is.

Cultural diversity

Israel, as you may or may not have heard, is indeed a very complicated place. There is no doubt that the tensions are high between Israelis and Palestinians and Hezbollah and Iran, which is often in the news. But day to day on the ground, Israel is a very safe place and safer than what I’m used to in the States. The crime rate is much lower than almost everywhere in the US, and I can walk around Haifa at night without ever feeling at risk. That is more than I can say for Santa Cruz and many parts of LA.

Haifa is a special place. It is a uniquely diverse city with a significant Arab population. The student body at the University of Haifa is over 30% Arab in descent and I can walk through hearing four languages in one hallway. The main temple of the Baha’i faith is here in Haifa.

There are Israeli Jews of all sorts of backgrounds, including Ashkenazi, Sephardic, Yemeni, Ethiopian and more. There are secular Jews, Conservative Jews, Orthodox Jews and the Haredim (Ultra-Orthodox), along with myriad others I haven’t learned about yet. There also is a huge population throughout Israel of Russian Jews who came here following the collapse of the Soviet Union. Russian is spoken heavily here and is on the street signs. Like America, Israel is a hugely diverse place and I believe could be a great strength for their future growth and prosperity.

Language and cultural challenges

As a secular American, there were some parts of Israel that have proved challenging to adapt to. The biggest challenge for me by far is that Israel’s national language is Hebrew, which is a very challenging language to learn. I now know the numbers, some letters and some words, but there’s no way I’m going to be able to pick up conversational Hebrew during my time here. And as all foreigners know, not being able to read and write makes literally everything about “adulting” more difficult. I have had to learn never to assume that English is understood here. I speak slowly and use hand gestures. I do everything in person, never over the phone. Trying to do something logistical over the phone has not once worked. Seriously, don’t even entertain the notion of trying to do stuff in English over the phone here.

Instead, I recommend going to the place you need to go, ask the person for help with a dumb blank smile on your face, and people will try to help you do what you need to do, whether that is opening a bank account, getting your bus card, or signing a lease for your apartment. People here are generally very direct and no-nonsense in everyday business dealings, but they also have proven very generous and willing to help me, which is not something I can say about service in America. However, on the rare occasions when I’ve found someone who speaks English, is available, and is exactly the person who can help me with the task at hand, I feel as though I should drop to my knees and thank the God of Abraham for his mercy. Day to day life here is tough for a non-Hebrew speaker.

If there was one aspect of life in Israel which I will openly complain about, it is Shabbat (from sundown Friday to sundown Saturday). In most of the Western world, we take for granted that Saturday and Sunday are the days of rest. But here in Israel, it is Friday and Saturday, and Israel is very hardcore about their days of rest. On Shabbat, any eating establishment that wants to be Kosher has to be closed. Almost all public transport is shut down.

There are a small number of more secular, diverse cities, luckily including Haifa, where a couple buses stay running Friday night and Saturday. But on Saturday, if I realize I need groceries, my choice is to splurge on a cab or walk 25 minutes down to the nearest 24/7 market (basically a convenience store). There is a reason Shabbat is a big deal in Israel and I get it. There is no other country on Earth where Jews of all creeds and colors can know that they will get to observe Shabbat in the way it was practiced by their ancestors. But for me as a secular person without a car, it presents a lot of logistical challenges.


Here is a list of other things I found notable and unexpected about life in Israel

  • They really like malls. There are new malls opening everywhere and they are always full of people. As an American, I think of malls as very last century, but they’re still the main social place here for many people.
  • They don’t really use mops. Instead, they use giant squeegees to clean their floors. I still don’t get how to use one.
  • When you sign a lease, many landlords want twelve pre-signed checks. I thought this was very strange (where do they keep them?!) and then noticed an option in the ATM to save checks for “safe-keeping.” Weird.
  • Israel is a cell phone paradise. I can get an unlocked SIM card with 30 gb of data, unlimited voice and text for $21.50. This is absolutely insane. How is this possible?
  • In Israel, they charge tenants a bimonthly property tax. That is annoying!
  • People say Israel is super expensive and yes, prices on food and basics are somewhat high by standards of some US States. But coming from California, I have been so relieved. I now can afford to live in my own apartment and pay <25% of my income on rent rather than 50%. I can once again stay under $10-15 a day on food which wasn’t possible for me in California for the last couple years. So I have more discretionary income for fun stuff which has been refreshing.
  • As I’ve noticed in Europe as well, it’s fun paying with coins! They have 10, 5, 2, and 1 shekel coins and I find myself actually using them, unlike the useless pocket change in the states that I just save to trade in later. There are around 3.7 shekels to the dollar.
  • They have an excellent bus system (except Friday or Saturday 😉 ). Buses come by frequently in all parts of Haifa, are clean, and cost about $1.50 per ride (1/3 less than that if you set up your student access card). The bus card allows you to connect for free within a certain time period as well.
  • Most locks in Israel use keys on the inside and outside. I’m not sure if this is an Israel-specific thing, or just something the rest of the world has that the US doesn’t, but it was surprising to see that I’d have to use my key to lock my front door from inside.
  • They have smarter crosswalks in Haifa that generally bridge over a median, with two separate pedestrian lights. You may have to stop in the middle but it means less risk of someone doing a turn and hitting you, and that is good urban planning in my book. Eilat has done away with streetlights altogether, completely converting to roundabouts. I frickin love roundabouts.
  • Israel has a semi private system of healthcare, but with generally very high quality care and low cost.
  • In Israel, life is completely transformed by their mandatory military service. While I have been out of college for a few years, many Israelis are only just starting college as they enter their late 20s after being discharged. So the student body trends older at Israeli universities.
  • I thought I’d stick out as an American goy being here, but apparently I don’t. People keep asking me for directions in Hebrew and Russian and I just say “sorry, English only”, and they look at me with disappointment. I guess I can say I look Jewish!

In conclusion, I have enjoyed my time in Israel so far, and I have found myself just watching life going on around me with great curiosity, because it is a very interesting place full of constant unexpected moments. Let me know if any of you visit anytime soon 🙂

Chameleons think bone fluorescence is sexy

Imagine you had bone spurs coming out of your eyebrows that fluoresced under UV light in a way that attracted mates. That’s what chameleons do, according to a new study in Scientific Reports! Chameleons have a lot of ways to talk to each other, including most famously with their ability to change skin color. But this bone fluorescence strategy is a more subtle way to show off their sexiness to each other, and it may appear in other places in the tree of life. I can assure you that many, many researchers are now looking at their specimens to see if their study organisms do this as well.

I’m Back!

As I branch out and prepare the first articles I’ve worked on in a while, I thought I’d set up a new home base to host my writing and contact information. So keep an eye out for posts about all sorts of topics, including my research and my numerous interests.