Beware! The Blob
Imagine you are on a trip to Paris. There is so much to see and do, but you decide to go to the local zoo. You are walking around, admiring all the interesting animals. There are beautiful big cats lounging about. There are enormous giraffes feeding on plants. You feast your eyes on some more unusual mammals, like the bat as well as some non-mammalian animals like snakes and birds of every color imaginable. Just when you think you’ve seen it all, you notice an exhibit with a crowd gathered. There are signs indicating it is a new exhibit. It’s in a dark room. You get excited. What could it be? A rare snake? An octopus? You squeeze your way through the crowd, peer through the glass and what you see on the other side is just a large, yellowish smear of slime. You wonder what animal could have made such a strange mess. And where is the animal; what is everyone looking at? You step back, look at the sign and read “The Blob” with a picture depicting the disgusting goop you saw sprawled out in the exhibit.
Why on earth would a zoo in a major city put such a creature on display? “The Blob”, affectionately named because of its appearance, was added to the Paris zoo and unveiled in October 2019, eliciting excitement from visiting crowds and the media. Unlike all the other park residents, the Blob is not an animal. It is a slime mold. It’s actually not even technically a mold; scientists just thought it was a mold because of how it looks, and the name stuck. It is, in fact part of the protist kingdom (as are amoebas and certain algaes). It has no mouth, no eyes, no muscles, no gut and, you guessed it, no brain. Its scientific name is Physarum polycephalum, meaning many-headed slime. It extends many branches out from its body, slowly exploring the world around. It’s max speed is only 5 cm/hr. The Blob it is unicellular. You read that right. The entire organism is only one cell. To put that in perspective, most cells on the planet are too small to be seen with the naked eye. This one can get as large as several square meters. Despite containing only one cell, the Blob contains hundreds to thousands of nuclei. This is very much unlike our classic view of a cell which only contains 1 nucleus. There are networks of “veins” throughout the huge Blob body which circulate fluid and allow transportation of materials. What is incredibly bizarre is that a single Blob can tear itself into fully functioning pieces, and the pieces can fuse right back together again.
Let’s talk about sex, baby
If you have heard anything about the Blob on your newsfeed or from friends, it was probably about how the Blob has over 700 possible sexes. The Blob takes non-binary to a whole new level! Before we jump into how this is possible, let’s briefly talk about how most mammalian sex determination works. One way to categorize sex is based on sex chromosomes. Most mammals typically have two possible biological sex options, male or female, which arises from their “sex chromosomes”. You’ve probably heard how a human fetus typically acquires an X chromosome from their mom and either an X or Y chromosome from their dad during fertilization. There is a specific gene on the Y chromosome that is important for sex determination. Humans are diploid, meaning they have two copies of each chromosome, including the sex chromosomes (excpept in cases such as in Down Syndrome, Edwards syndrome, and others, where an individual has three copies of a specific chromosome). When humans make gametes (sperm and eggs), the sex cell usually only gets one copy of each chromosome (therefore it is haploid). Then when the two gametes fuse together during fertilization the resulting zygote is diploid.
Physarum polycephalum are far more complicated. The large, bright yellow Blob which is on display in the zoo is just one step in the large, complex life cycle of the Blob. What we see is the diploid (meaning two genomes) plasmodium. Unlike in humans, which have one sex determining gene, the Blob’s genome has three. So each diploid parent can make 8 (2^3) different types of gametes with respect to sex. And on top of that, each sex gene has many different types, unlike in humans which have two types (X or Y). So when you do the math (depending on how exactly you count everything up), you get anywhere from 500 to 720 different sexes . Imagine trying to use Tinder if that was the case for us. But in fact, it turns out, that a Blob can mate with any other Blob as long as the two Blobs aren’t the exact same sex. So it would actually be a lot easier to find a mate.
If I only had a brain
Now you may be wondering how this article about an organism that does not have a brain, or even a single neuron, slipped into a neuroscience blog. While all the stuff about the Blob only having one cell and hundreds of sexes is cool, what has really been astounding scientists is the Blob’s ability to learn and remember, despite not having a single trace of a nervous system. It was traditionally thought that simple organisms with no nervous systems were capable, at most, of simple stimulus-response behavior. Recent studies, however, have shown that protozoa such as the slime mold, Physarum polycephalum are capable of complex decision making and problem-solving strategies.
Some thought-provoking experiments
Briefly, I will outline some of the more interesting studies done, though there are many others I will not get to. First is a study by researchers in Dr. Toshiyuki Nakagaki’s lab, where the team laid out oats (one of the Blob’s favorite foods) in a pattern on a petri dish which matched the geographic distribution of Tokyo and 36 surrounding towns. When the Blob was left to explore it eventually settled on a pattern that almost exactly replicated the Tokyo railway system. This group and others have also done similar experiments with many other large cities, with the results always the same. The Blob can strategically and efficiently position itself in the most cost-effective position for acquiring nutrients. While this doesn’t necessarily prove the organism is intelligent, it does illustrate its capability to solve complex spatial problems. This cost-effective position for acquiring nutrients used by the Blob, mirrors how human civil engineers must design the most efficient strategies when determining how railway systems should be laid out.
Another study, by Dr. Audry Dussutour’s lab, was meant to determine whether Physarum polycephalum are capable of habituation, a type of memory where a stimulus is learned to be overlooked due to lack of necessity. Think of your ability to tune out the sound of your heater, because it is on so often and not conveying any important information to you. What Dr. Dussutour’s team did was place an aversive stimulus, either caffeine or quinine (harmless but bitter chemicals), between the Blob and its favorite food, oats. Initially it took the Blob a very long time to traverse the aversive stimulus to receive its reward. Over time, though, the Blob was able to learn that the stimulus was, in fact, not relevant and it would cross right over as if it weren’t there. However, if a different aversive stimulus than the one the Blob was habituated to was placed in the way, it would go back to very slowly crossing over to the oats. This study was even taken a step further. Since slime molds can fuse together, the team wanted to see if a habituated mold fused to a naïve mold would retain the “memory” that the stimulus is not bad. They tried fusing pieces of habituated and naïve molds into new molds with various ratios of habituated to naïve and every single new mold which contained a part of a habituated mold “remembered” that the aversive stimulus was fine to cross. This suggests that by fusing together, slime molds can essentially teach each other information.
There is one final study I want to mention. As somebody who is catastrophically incapable of keeping track of time, I am always impressed by animals that can precisely keep track of time intervals. Especially when that animal isn’t even an animal but a single- celled Blob. In this study by Dr. Tetsu Saigusa’s group, a Blob was left to hang out in a warm, damp environment, which is their favorite, where the Blob would be allowed to explore. Every 30 minutes the team would reduce the temperature and the humidity, creating an uncomfortable living condition. In response the Blob would essentially stop exploring until it warmed back up. After a few rounds of this the team stopped dropping the temperature. Despite the fact that the environment stayed warm/damp the Blob would still slow down every thirty minutes in anticipation of the change. After a few bouts of being fooled it would realize and stop prepping for the cold. This was also performed at 60-minute intervals with the same result, suggesting the Blob has an internal clock and is capable of keeping track of time. This type of behavior is often associated with a specific type of memory called episodic memory.
There has been a surprising amount of disagreement amongst scientists about whether slime molds like the Blob are intelligent or capable of learning. There are the more traditional folks who believe an organism must have a brain to learn or be smart, and there are more progressive individuals who are open to the idea of non-neuronally derived intelligence. Either way, nobody can dispute the fact that slime molds are capable of some pretty remarkable behaviors. There are researchers who want to use them to study the origin of learning and memory and also as a simpler model of information processing and integration. Some scientists are even taking things to the next level by trying to use slime molds to build bio-computers and to drive robots. One thing is for sure, slime molds like the Blob are fascinating and almost alien-like. Organisms like these make it clear that there is so much life out there that we know essentially nothing about. And there are probably weirder creatures coming to a zoo near you in the future.
References  Boisseau, R., Vogel, D. and Dussutour, A. (2016). Habituation in non-neural organisms: evidence from slime moulds. Proceedings of the Royal Society B: Biological Sciences, 283(1829), p.20160446.  Iwanaga, A. and Sasaki, A. (2004). EVOLUTION OF HIERARCHICAL CYTOPLASMIC INHERITANCE IN THE PLASMODIAL SLIME MOLD PHYSARUM POLYCEPHALUM. Evolution, 58(4), p.710.  Saigusa, T., Tero, A., Nakagaki, T. and Kuramoto, Y. (2008). Amoebae Anticipate Periodic Events. Physical Review Letters, 100(1).  Tero, A., Takagi, S., Saigusa, T., Ito, K., Bebber, D., Fricker, M., Yumiki, K., Kobayashi, R. and Nakagaki, T. (2010). Rules for Biologically Inspired Adaptive Network Design. Science, 327(5964), pp.439-442. Blob gif: GIPHY Robin Williams Lol GIF By Laff