May 2005 Archives

Everyone is familiar with the increasing divisions and compartmentalization of the sciences that occurred as they went through school. In grade school, we were taught Science; in high school we took Physics, Chemistry, and Biology; at the university we could major in Aquatic Biology, Biochemistry, Cell Biology, Microbiology, Zoology . . .

And then, for those who went on to do professional science, they got jobs as Biochemical Phycologists, Mammalian Physiologists, Evolutionary Developmental Biologists, and so on. This partitioning of science would appear to be an example of ontogeny recapitulating phylogeny*. Once, every man who fancied himself a scientist dabbled at some point in all branches of the field, as children still can do today. Now, at every research institution you can hear scientists prefacing their statements with:

"I'm no evolutionary biologist, but . . ."
"Speaking as a molecular geneticist . . ."

What happened to the days when we were all naturalists? I really like that term, <i>naturalist</i>. It brings to mind great, adventurous people like Charles Darwin and John Doolittle. (Yes, the latter is fictional. So what?) People who traveled from continent to continent, collecting samples of animals, plants, soil, analyzing them on site, pockets bulging with magnifying glasses, preserving chemicals, glassine envelopes, notebooks and pens. People whom you could ask about any aspect of natural history whatsoever.

The problem is the seemingly infinite, fractal complexity of Nature. The more we know at one scale, the more openings we see down to the next scale, and still more the next, so that as we painstakingly add to the body of scientific knowledge, it seems that all we are doing is adding holes to be filled. Thus you may start out wondering why the sea hare lives where it does, and begin to examine the distribution of the algae it eats, and then, seeking to explain the algal distribution, you find the algae is suited to particular salinities, an inclination which must be due to its physiology, which is in turn defined by its cellular structure... before you know it, fifty years have passed and you have become an expert on Phycological Cellular Physiology, and you don't remember what a <a href=http://www.brembs.net/learning/aplysia/aplysia.html>sea hare</a> is.

Henry David Thoreau writes, "Where is this division of laber to end? and what purpose does it finally serve?" He is talking about architecture, not science, and fervently arguing that men should build their own houses, rather than do as the cuckoo does and live in another's nest.

While there is a certain romantic appeal to the idea of building one's own house, just as there is to being a naturalist, perhaps in this modern day neither is any longer practical, or, for that matter, practicable. I should like to borrow Thoreau's idea of building in order to make the opposite argument; that we are engaged in the highest sort of architecture by building upon one another's ideas rather than (to be cliche) reinventing the wheel. Ideas naturally lead to other ideas, and experiments to further experiments. If a single naturalist worked alone, and attempted to follow at a time all these leads and branching paths, how slow would be his progress! If, on the other hand, he may devote himself to the one which holds the most interest for him, while his fellows may borrow his previous work to begin their own work, how swiftly will each man become specialized and how speedy will be their progress.

However, I allow that this specialization will quickly become a hindrance if they lose contact with one another, or do not put in the effort to understand all the work that has gone before. Even if a man has his house built for him, he would do well to know at the least what part to stand in, in the event of an earthquake.

No matter how specialized one's field, it seems not only desirable, but necessary, that a researcher be able to see where the research fits into Nature as a whole. Maintaining this broad perspective, I think, will keep one from loving the work for its own sake and worshiping the techniques, which is something that is easy to fall into, especially with some of the very complex molecular techniques out there. No doubt they are very beautiful in themselves, but they are meant to be tools for answering questions about the world around us. Having in mind the connection between one's own work and the world at hand is also an enormous aid in explaining said work to family, friends, and public.

This broaches another aspect of specialization, namely, that friends, family, and public often desire and expect all scientists to be The Scientist, diversely knowledgeable. Thus, in addition to maintaining some breadth for the sake of personal housekeeping, it becomes necessary to retain that high school Chemistry, Physics, and Biology which everyone else who entered more sensible careers has had the privilege of forgetting, because they will ask you about it. While your mother may be aware that you are a Phycological Cellular Physiologist, that won't stop her from expecting you to know why the human body needs vitamin D, or how bubbles form in boiling water.

And I feel that there is a certain obligation, for those of us who have been lucky enough to remain in school indefinitely, not to forget what we have learned, not to lose breadth in pursuit of depth, and to retain the sense of adventure and the connection with Nature felt by children studying Science in elementary school--and by Darwin and Dr. Doolittle.


* "Ontogeny recapitulates phylogeny" was a theory proposed by Ernst Haeckel in the mid 1800's. He claimed that the development of an organism from egg to adult illustrates the evolutionary history of that species over time, as the embryo passes through stages resembling all of its ancestors. Famous example: "gill slits" in human embryos. Neat idea, but it's been mostly discredited, although there are certainly some interesting connections between ontogeny and phylogeny. This, incidentally, is happening to theories in biology ALL THE TIME, and leads me to formulate a Theory of Publication, to wit:

There are two ways to publish big, important papers.
1. Make a broad, sweeping generalization that synthesizes diverse sets of data.
2. Gather more data to show that said generalization is in fact an oversimplification of a very complex system. Because if there's one thing that we consistently keep showing about biology, it's complexity.

The Theory of Publication is, of course, an oversimplication.

The spicy component of peppers is called capsaicin. It's an interesting molecule, because it doesn't actually bind to taste receptors; it binds to thermoreceptors. This means that capsaicin actually "tastes" like heat. This fascinates me. Normally we can't taste much heat because if something gets that hot in temperature, the tongue gets burn damage. But capsaicin literally tastes like burning, without actually burning.

It's curiously synesthetic.

Synesthesia, which refers the crossing of sensory modalities (seeing sounds, hearing tastes), raises the question of just what a sense is, anyway. By convention we think of the five human senses as sight, hearing, taste, smell, touch. To be more precise/pedantic, these are sensory modalities and the terms are olfaction, gustation, vision, audition, tactition.

Actually, it is not so straightforward. We also have, as previously mentioned, a sense for thermoreception, as well as senses for balance (vestibular), pain (nociception), and locating ourselves in space (proprioception).

When it comes right down to it, senses aren't nearly as clearly delineated as we were taught in elementary school. What makes a distinct sensory modality? Is it a distinct type of receptor? Then we're already a bit confused with tasting capsaicin, and it gets worse--hearing, balance, and tactition are all mediated by mechanoreceptors, receptors that sense physical pressure such holding a pencil, or having a sound wave push against your ear.

The senses of smell and taste both use all kinds of chemoreceptors that are sensitive to all kinds of chemicals. So what's the difference? Standard reply is that smell detects airborne chemicals, while taste detects water-soluble chemicals. It must be noted, then, that aquatic animals have no sense of smell--although it may be somewhat less disturbing to think of sharks smelling blood from miles away rather than tasting it. But even on land there are some hazy cases; mice have a vomeronasal organ which detects water-soluble chemical cues carried by the nasal mucus (=snot). This information is described in the scientific literature as mapping* to an anatomically distinct set of olfactory neurons and brain centers. So is this water-soluble olfaction?

Incidentally, the VMO is not unique to mice. It's present in a wide variety of terrestrial vertebrates, including humans.

However, there are a number of intriguing sensory modalities that remain entirely unavailable to humans. One of the most outlandish is electroreception, developed in a number of fish and, uniquely among mammals, in the platypus. These organisms can detect changes in nearby electric fields, and some even generate their own. While discussing electroreception one must also mention magnetoreception, famous for allowing birds to orient themselves to the compass directions for migratory flights. If you remember your E&M from high school physics, you'll recognize that electric fields generate magnetic fields and vice versa, so what's the difference in sensory modalities? The main distinction between electroreception and magnetoreception as I understand it is that sharks and platypuses are sensing disturbances in small local electric fields, while birds are paying attention to the Earth's magnetic field as a whole.

So we could also categorize sensory modalities based on the type of energy they recieve and transduce. All cues come in some form of energy, be it light or vibration or gross matter. I should like to classify energy cues thusly:

chemical
light
pressure
heat
electromagnetic

We already know chemicals (matter) are energy, and light and heat and pressure are just different kinds of waves or vibrations, and if the physicists ever come up with their Grand Unified Theory we'll know that all forms of energy are the same anyway. I feel this rather esoteric thought ties in nicely with the title of this entry, which refers to the yogic tradition of referring to the five senses as five horses drawing the chariot of the body, where the mind is the charioteer. Yoga means union, and if all the senses are just energy receptors, and the mind is made up of electrical impulses, and matter is energy, then perhaps horses-charioteer-chariot are all one.

But that's not a really useful perspective for studying squid pheromones, which may be the next topic of rambling...

* The astute reader will notice I've been skirting around the issue of classifying sensory modalities by mapping them to different regions of the brain. That's because I know relatively little about neuroscience and it's all much more complicated that I want to get into right now.

...both literally mean "living together", only they come from different roots.

co: Middle English, together; from Latin com, together, with; from Indo-European kom, beside, near, by, with habit: from Latin habitare, to dwell; frequentative of habere, to have; from Indo-European ghabh, to give or receive sym: from from Greek sun, together, from Indo-European ksun, with biosis: from Greek bios, life, from Indo-European root gwei, to live

Of course, they have entirely different connotations. Imagine telling your parents that you and your significant other have decided to enter into a symbiotic relationship. Calling a relationship symbiotic has the additional effect of making most people think of it as mutually beneficial.

In a strict sense, symbiosis doesn't mean that at all. Ecologists use it for its literal definition, and then categorize the different kinds of symbioses based on the benefits to the participants. A symbiosis in which all parties benefit is called a mutualism. If one party benefits from the relationship and the other is indifferent, then it's a commensalism*. And if one party benefits at the expense of the other, we call it parasitism.

And today, my friends, I am here to talk to you about parasites.

Specifically, the phylum Dicyemida (or Rhombozoa, or Mesozoa... but that's a problem for the taxonomists). Dicyemids are little worm-like creatures that live exclusively in the renal appendages (read: kidneys) of cephalopods. Yeah, weird. That means they are basically swimming in squid urine. What possible benefit this could provide to either worm or squid is difficult to imagine.

The problem with all these symbioses is that, as in any relationship, it's often difficult to tell just who is getting what out of the association. Organisms are labelled mutualists, commensals, or parasites based on the perspective of the observer, which may be quite different from the participants. Certainly a number of cases are clear-cut parasites, such as malaria or tapeworms. Dicyemids, by contrast, are called parasites although we have yet to show any effect on the host cephalopods, benficial or detrimental. Not only that, but no one knows for sure how they infect their hosts in the first place, or for that matter, why they infected them in the way-back-then first place.

Dicyemids are extraordinarily simple. They're eutelic, which means each individual adult of a given species has exactly the same number of cells as all the other adults of that species. This has attracted a number of cellular biologists to study their cell lineages--tracing the history of each cell back to the zygote that gives rise to the whole organism. We're talking on the order of about twenty cells per organism here--these guys are not very big and they're not very complex. No organs or tissues of any sort disturb this perfect parasitic simplicity.

So they were originally classified as Mesozoa, which means "middle animals" and sticks them somewhere in between the Protozoa (first animals, single-celled critters) and the Metazoa (after animals, everything else). But then the geneticists got interested and did some sequencing work on dicyemids to show that they actually seem to be extremely simplified relatives of the Lophotrochozoa, a big group of metazoans which includes squid.

Parasitic simplification is just part of the larger phenomenon of symbiotic simplification. If you're living with someone else, particularly if you're living inside them, it turns out you can get them to do a lot of things for you, like digesting food and dispersing your offspring, towards which you no longer have to allocate energy. And this is why so many parasites can no longer live when separated from the hosts... I feel a tangent coming on.

The inability to reproduce independently is a derived character in parasites, while it is inherent to viruses. At least, that's the presumption. Might that be a little... presumptuous? Is it possible that the viruses we know today evolved from some RNA lifeform that could reproduce on its own, and secondarily lost the ability?**

Back to the point, which is: squid worms!

With all the geneticists and cell biologists mucking around with dicyemids, there aren't a whole lot of ecologists poking at them. And this means that we still don't know what I consider to be the really interesting aspects of their biology: how they interact with their hosts and to what end.

It seems a few experiments could at least give us some leads into this. First off, the infectious stage and method of infection need to be pinned down. That could pretty easily be done by raising octopuses in the laboratory and exposing them to various life stages of dicyemids at various points in their lives. Once the infection of hosts can be controlled, effect of infection of host fitness can be assessed. And if the dicyemids themselves can be cultured outside of the host, providing them artifically with various aspects of their normal environment could tell us how they sustain themselves in the cephalopod kidney.

Look for publications in a few years. Or decades.



* Middle English, sharing a meal; from Medieval Latin commensalis; from Latin com, with, and mensa, table.

**I'm totally making this up. I must remember to look it up and see if anyone else has had the same idea.