The Amazing Social Amoeba!

Multicellularity is an astonishing feat of communal sacrifice. With the exception of sperm and egg (the "germ line" cells), the 40 trillion cells currently in your body will dutifully perform their particular charge to maintain the whole, intricately arranging themselves to form your arteries, lungs, liver and brain, without ever having a chance to meaningfully reproduce. Many will die on command like fascist soldiers in a bad sci-fi movie. Even for the Genghis Khans of the world, a vanishingly small minority of the cells in the body produce descendants that outlive the individual of which they are a part. The primary imperative of life on earth is to reproduce (save for humans), yet multicellularity seems like a coordinated renunciation of that mission. Cells instead opt to specialize and curtail their reproductive potential (except for cancer cells) in favor of becoming part of something larger. Despite its seeming improbability, multicellularity has evolved dozens of times in the history of Earth, in both familiar and strange branches on the tree of life. 

Picture: Phylogeny Friday

Animals and Fungi are two of the more familiar multicellular lineages and are both members of a group called the "Unikonts." Indeed, fungi (like mushrooms, brewer's yeast, and athlete's foot) are much more closely related to animals than to plants. Amoebae, the microscopic, one-celled blob-looking organisms, are fellow unikonts, though more distantly related to animals than are fungi. One lineage called "social amoebae," or cellular slime molds (Dictyosteliids), conduct their lives in a bizarre twilight zone between the unicellular and multicellular. Social amoebae scavenge for bacteria as single cells, roaming in forest soils. But when times get tough, they aggregate together and form a visible, multicellular being called a "slug" or grex, about 3 millimeters long. This "slug" then migrates to more bountiful scavenging grounds, where it forms a fruiting body (sorus) on top of a stalk and ejects amoeba spores (kind of like a mushroom). Here are some videos:

These organisms have much to teach us about how multicellularity evolved and under what conditions. Not surprisingly, some of the genes and pathways social amoebae use to guide the formation of the "slug" differ from those used in animals and fungi. However, some aspects of cellular communication and development are similar across these three groups. As (distant) relatives of animals and fungi, social amoeba inherited many of the same genes from our common ancestor. In frogs, humans, and mushrooms, variants of these genes encode molecular signals that cells use to communicate and direct the proper development and growth of multicellular bodies. In social amoebae, they regulate the formation of the "slug."

Like other multicellular organisms, social amoebae exhibit self-sacrifice. The cells that make up the stalk of the fruiting body become rigid enough to hold the amoebae on top of them, and in the process die. This feature of "slug" behavior is of intense interest to those studying the evolution of multicellularity, and of the biological "altruism" that makes it work. The traditional explanation for the evolutionary advantage of altruism hangs on relatedness. You share roughly 50% of your genetic material with each sibling; if you die saving your sister from a burning building, she may live to pass on "your" genes to her offspring. Such is the cold, cruel logic behind the famous (in some circles) J.B.S Haldane quip "I will jump into the river to save two brothers or eight cousins." The same logic underlies ant and bee colonies where sterile workers serve their mother queen, and the behavior of cells in multicellular organisms. A kidney or skin cell waives its reproductive abilities in favor of the sperm or egg, which shares 100% of its genetic material.

Photo: Rodrigue Hamende

Indeed, social amoebae form "slugs" with their close relatives, and this helps curtail the spread of "cheaters" in their ranks. "Cheaters" reproduce rampantly, or suck resources from the whole without contributing their share; these cells are the rough equivalent of cancer cells in humans. The important difference is that social amoebae are fully capable of producing viable offspring that reproduce indefinitely. With the bizarre exceptions of transmissable tumors in Tasmanian Devils and dogs, cancer cells in animals are ultimately doomed to go down with the ship; they have no means to continue their spread following the death of the individual from whence they came. This difference means that natural selection acts against alleles (genetic variants) that increase cancer risk in animals, since these alleles cannot be passed on beyond the proliferation of the cancer. But cheater alleles in social amoebae could be selected for, if the free-loaders can jump off the "slug" and reproduce on their own. However, "slugs" can discriminate kin from strangers, and aggregate with their relatives, who are more likely to share their altruistic alleles. "Slugs" with a high proportion of cheaters are likely to fail, so those alleles won't be passed on.

Social amoebae are not a "missing link" between single- and multi-celled organisms; they are not our grandmothers but rather our distant cousins, and they have been an evolutionary success in their own right. There is no good reason to think they are evolving to become fully multicellular. However, the configuration of their life cycle, straddling the divide between single- and multicellularity, allows us to investigate the mechanisms and circumstances driving cellular communication and cooperation. We can see in them an alternate version of the rulebook by which we are built.

Monitoring Movements of Mysterious Marine Megafauna

I wonder about the ocean.

The smell of a salty breeze, the curios washed ashore, the miniature worlds in tide pools, the rolling expanse of waves - I instantly revert into a 6-year-old with a bucket and a net. That's just as well, because childish curiosity is probably the most appropriate response to the epic vastness and depth of the sea. Fantastical alien worlds lie just under the surface, out of reach. What is going on in there?

beep boop
Photo: nasa.gov

Centuries of dedicated scientific inquiry have yielded boatloads (sorry) of information about the flora and fauna of the ocean. Just as on land, scientists have used a variety of tools to chip away at a wall of questions about the ecology, life cycles, distribution and evolution of the menagerie of life in the ocean. As our analytical techniques and technological toolset grew, we were able to address old questions and discover new phenomena that hadn't even occurred to us. A system of satellites, buoys, and drifters was employed to precisely map oceanic currents, a dream to Magellan and Drake. The accidental spill of 28,000 rubber ducks from a container ship in 1992 also helped. As knowledge expanded, we encountered new phenomena we had never anticipated, generating still more questions. Piloting the deep sea submarine "Alvin," Robert Ballard found whole complex ecosystems at the hydrothermal vents on the ocean floor that we had never imagined." These ecosystems derive their energy not from the sun, but from sulfides belched into the ocean from deep in the earth.

Party down here
Photo: http://serc.carleton.edu

One of the particularly frustrating remaining mysteries of the ocean is where large animals (megafauna) go and what they do. Sharks, whales, seals and turtles break the surface here and there for a short while and then slip back under the waves just as mysteriously, leaving us wondering where they were going and why. Are the

Great White Sharks seen off the coast of Cape Cod in August the same individuals seen around Florida? Where do hammerhead sharks go when they're not cruising around reefs? Why are whale shark feeding congregations 70% male - where are the females? These animals are some of the most majestic and awe-inspiring in the world, and we have no idea what they're doing most of the time.

Where the ladies at?
Photo: oceana.org

Satellite tracking studies, in which small devices loaded with sensors are attached to these animals, have done much to fill in the gaps in recent years. A lot of this information is helpfully compiled at http://www.topp.org/, and through it we have learned a great deal about the lives and migrations of marine megafauna. Whale shark feeding congregations are largely male because females are likely at sea-mount nurseries off in the open ocean, where there are fewer predators. Great Hammerhead sharks similarly migrate out to particular points in the middle of the ocean, outside of their previously-known range, and into international waters where the protections on hunting them can't be enforced. These sharks migrate in astonishingly straight lines, leading to hypotheses that these sharks navigate using the magnetic signatures of the earth, a mechanism called "geomagnetic topotaxis." Great White Sharks also travel huge distances, but take more meandering courses.

Satellite tracking studies shine a light on previously unknowable aspects of some of the most impressive animals on Earth. We're slowly building an idea of where and why they congregate, and how they navigate the ocean. As knowledge is uncovered, new questions arise; what kind of sensory systems allow to hammerheads to sense magnetic fields? As with all science, we build new tools and use them to answer old questions, and in the process stumble upon the unexpected. Inevitably, in exploring the shrouded corners of the world, we discover the depths of our own ignorance.

The NSA is leading us to a dark place

The United States has a long history of maintaining covert intelligence agencies, and that can make sense in the realpolitik, game theory world of geopolitics. During the Cold War, knowing the behind-the-scenes position of the U.S.S.R likely helped avoid mis-steps that could have resulted in nuclear catastrophe. Likewise, on issues such as US-China relations, Iranian nuclear negotiations, and trade talks, there is a place for covertly acquiring information about the intentions of other players to avoid serious blunders. Spying is often called the "world's second-oldest profession," and it's not going anywhere soon.

That said, the growth of the military-intelligence-industrial complex since 9/11 is unprecedented in its scope, brazen unconstitutionality, and lack of accountability or oversight. Collecting data (or metadata) about the communications of millions of citizens and non-citizens alike, without a warrant or an even a stated suspicion, is clearly a violation of the fourth amendment of the Constitution, no matter how much garbled legal justification the intelligence community condescends to toss us. Instead of allowing the NSA to collect the whole haystack in hopes of finding the needle, we need to return to traditional police work of following leads. As the fourth amendment declares: "no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized." If we choose as citizens to accept the NSA's assertion of authority to collect "things" (metadata is a thing) without warrant, we are agreeing to retreat on the fundamental ideals of our nation.

"Verily, we shall remove SSL certificates betwixt the public internet and Google Cloud" 

Furthermore, this spying program has failed to provide us with workable intelligence. The NSA has recently admitted that their surveillance program has foiled at most one or two terrorist plots in the US. The increased scope of our spying has also backfired dramatically on several fronts. The NSA's programs have weakened the structure of internet security for everyone, and raised doubts about products offered by US tech companies, risking about $35 billion in sales. Our major alliances, which have a much more real and substantive effect on security than one or two terrorist plots, are being greatly strained by revelations that we're tapping their communications to an unprecedented extent. In the meantime, the image of the USA around the world is becoming one of an enormous, ominous, secretive empire, dealing illegal assassinations from airborne robots and collecting every communication. It is hard to imagine that this does not effect our ability to partner with state and non-state actors around the world. With all this considered, a reasonable argument could be made that the power grabs made by the intelligence community in recent years have done more to weaken U.S. security than to enhance it.

After the abject tragedy of 9/11, Americans shifted priorities in the (dubious but workable concept of a) balance between security and freedom by enacting the patriot act and funneling hundreds of billions of dollars to spy agencies. This recalculation was understandable at a time of great trepidation, but it is now time to seriously reassess the choices we made. I do not deny the need for good intelligence, nor do I doubt the motives of the people working for these agencies. The military-intelligence-industrial complex, like all bureacracies, has a tendency to perpetuate itself, and to grab power - their evil is banal. Our spooks have a certain threat-centered perspective, and that perspective is blind to important priorities that we have as citizens, such as maintaining open relations with our allies and a secure internet. We have to accept that no amount of spying or drone striking can ever guarantee that there will never be a terrorist attack again. A reduction in the risk of a terrorist attack from 1% to 0.1% is not worth throwing our principles out the window and becoming the death-robot in the sky. 

Truth and Beauty: Sea Slugs

Check out this National Geographic photo gallery of gorgeous sea slugs by photographer David Doubilet! These sea slugs, called nudibranchs, have evolved zany colors for your personal enjoyment, and also to warn predators about the toxic compounds they contain. Some nudibranchs make these compounds themselves, but many extract and concentrate toxins from the sponges they eat.

Photo: Alexander Jenner

But retaining toxic compounds is far from the only trick that sea slugs pull. Fellow

Soaking up the rays
Photo: EOL

Euthyneurans (the group that contains nudibranchs) like Elysia chlorotica have evolved "kleptoplasty," whereby they extract the photosynthetic structures (chloroplasts) out of algae they eat, and retain them within special cells in their guts. This allows the slug to get energy from the sun like a plant, for up to 9 months after they eat the algae - Elysia is a temporarily photosynthetic animal!


Let's all take a second to think about how cool it would be to photosynthesize.

Nobel Prize if you figure out how this works!
Photo: Genny Anderson

Another Euthyneuran, Aplysia californica, has been extensively studied for decades as a model of learning and memory. Eric Kandel won the Nobel Prize in Physiology in 2000 for this research. Aplysia has a relatively simple nervous system, making it easier to study what's going when the slug learns. Kandel and others mapped out changes in individual synapses (the connections between neurons, where the action happens) as they conditioned the slugs the way Pavlov conditioned his dogs. This research regime showed in detail the mechanics of Hebbian plasticity, the theory that "cells that fire together, wire together*." That is to say, neurons form stronger connections with other neurons that they communicate with frequently. It's like the way foot paths form after a fresh snow - as more people follow the tracks laid by the first person, the path becomes more defined. This is a fundamental principle in neuroscience, and explains a good deal about how our brains change according to the ways we think.

Photo: Chika Watanabe

Each strange branch on the tree of life has its own marvels, and I find that taking time (not easy, I know) to take a good look at something as "lowly" as a sea slug can really bring a fresh perspective and appreciation to life. I hate to film a shopping bag here, but beauty and truth are often hiding in the weirdest corners, as these sea slugs show. It's a big part of why I study biology, although there are many ways to reach the sublime outside of living things. We are surrounded by beauty, even if that beauty is a way of saying "I'll kill you if you eat me."

*Dr. Carla Shatz probably said this first

Phylogenetics

Note: this was originally in my post about the application of phylogenetics in language, but several people pointed out that it should really be its own post.

Photo: UC Museum of Paleontology

Evolutionary biology has been revolutionized over the last ~40 years by phylogenetics, a way of using information about the traits of organisms to figure out how they are related to each other (explanation here). This tool has yielded an immense amount of knowledge about how different groups of species are related to each other, when they diverged from each other, and which traits are likely important in the evolution of a given group. Basically, the idea is that species that are more similar to each other are likely more closely related, based on the assumption that species descend from other species, and gain modifications along the way (that is, that evolution is real).

Phylogeneticists (in their earlier form called cladists) would measure and score traits like producing milk, having fur, and producing body heat, and show quantitatively that there is a group (mammals) that all come from a common ancestor that had these traits. This is based on the assumption that the simplest explanation for the distribution of these traits is the one that involves the fewest changes across the tree, and that the simplest explanation is the best. So the simpler explanation for the distribution of the traits of milk, fur and body heat across animals is that the ancestor of all mammals had all these traits and passed them on to its descendants, instead of these traits evolving independently many times. Phylogeneticists had to deal with difficulties like the fact that birds also produce body heat (convergence), but by carefully scoring information about traits, they could tell us that whales are not fish and bats aren't bugs.

Things got substantially more intense
Photo: codoncode

Of course, phylogenetics has become increasingly complicated since those early days. Now, instead of treating all traits as equal, evolutionary biologists build models for how likely different traits are to change. We count the likelihood of evolutionary shifts between species instead of just the number of traits they have in common, because fur color is more likely to change than heart structure. Another major change is that biologists now look at DNA and Protein sequence for most of their data instead of looking at traits like bone structure or number of toes. Our models and methods have become significantly more sophisticated, and phylogenetics is now a relatively old and mature field.

Evolutionary insights into language and culture

The verb "to spit" may be one of precious few words preserved from the common ancestor of all Eurasian languages. The word "huh," as in "what did you just say," has arisen* in many languages around the world. These findings come from two of several recent studies that use methods developed in evolutionary biology to discuss the evolution of language. Specifically, they employ a method called "phylogenetics" that uses information about the characteristics of species to figure out their relationship to one another. There have been some basic errors,*  as you would expect in a discipline taking up new methods. However, these studies hold promise for getting at questions about the history and spread of language, and also understanding how language evolves.

The fundamental assumption of phylogenetics is that species descend with modification, and in theory the method should work for anything that does. Like language, or culture.

Hey, look at that!
Picture: Jack Lynch

The new wave of linguistic and cultural phylogenetics is driven by the insight that languages and cultures, like species,  evolve and diverge. But that insight itself is not new. The understanding that languages descend from each other goes way back to before Charles Darwin was born, as European explorers noticed that their tongues shared similarities with Persian, Gujarati and other languages they encountered. Darwin himself gives a shout-out to the parallels in The Origin of Species, saying:


"Yet it might be that some ancient languages had altered very little and had given rise to few new languages, whilst others had altered much owing to the spreading, isolation and state of civilisation of the several co-descended races, and had thus given rise to many new dialects and languages. The various degrees of difference between the languages of the same stock would have to be expressed by groups subordinate to groups; but the proper or even the only possible arrangement would still be genealogical; and this would be strictly natural, as it would connect together all languages, extinct and recent, by the closest affinities, and would give the filiation and origin of each tongue."



The possible application of phylogenetic methods range far and wide in anthropological, linguistic and sociological research. In addition to the linguistic papers cited above, researchers are now publishing papers about the phylogeny of  "Little Red Riding Hood", Turkmen Textiles, and marriage practices. Aside from just determining relationships, phylogenetic analysis can also tell us about which practices and language structures change faster or slower, which might hint at their centrality and importance. For example, the first paper I cited in this post uncovered that the words for "we," "what," and "thou" are amongst the slowest-changing in the Indo-European language family.

However, there are many reasons to doubt that phylogenetics will be as successful at untangling linguistic or cultural relationships as it was for biological ones. Though biological evolution can be chaotic and hard to predict, the limited number of possible changes in DNA code (you only have four letters to work with) make it easier to predict how likely different kinds of changes will be. In addition, there are rules for the flow of information such as the so-called "Central Dogma" of molecular biology. While many, many exceptions have been found to these general rules, they provide a relatively stable framework to judge the likelihood of evolutionary events, which is crucial to building an accurate tree of relationships.

Right chaps, should we go with "Porc" or "Pig?"

It remains to be seen whether these models of change can be worked out for linguistics or cultural evolution. Much depends on whether there actually are generalizable rules for the likelihood of developing an irregular verb, or changing a phoneme, or adding in certain plot points to your mythology. Perhaps the linguistic changes to English following the Norman invasion can someday be modeled like a hybridization between two species. There are researchers asking these questions, and the race is on to find general rules of linguistic and cultural evolution.

I somehow doubt that these rules will emerge, though I hold out more hope in language than culture. Perhaps it is pessimism in the face of the complexity of the problem. Humans are wild and chaotic in the way we dance with our languages and cultures, subverting and transforming meanings and sounds, and making synesthetic connections between completely separate realms of thought. Maybe I harbor hope that that can't be fit into a mathematical model. In any event, the next few decades of linguistic and cultural research should be interesting to watch.

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*This is an example of a mistake that the authors made in their use of evolutionary language, and I will introduce some of that terminology here - if you're not really into evolution, this might be dry and it's OK if you stop reading now:
In the "huh" paper, the authors conclude that the word arose independently through "convergent" evolution without knowing if ancestral languages have this word. That is a basic mistake: convergent evolution is when a trait evolves in two separate lineages, but wasn't present in the common ancestor of those lineages.

If the word "huh" was convergent, then English and Hindi would both have the word "huh" but the Indo-European ancestral language that English and Hindi descent from would lack this word. The authors respond to that by basically saying that we should strip the term "convergence" of all meaning by "generalizing" it, citing a paper that suggests merging the terms "parallel" and "convergent" evolution. Their argument is not very convincing":

"We use ‘convergent evolution’ as a general term for the independent evolution of similarities in form and function. When ancestral forms are known, a distinction can be made between form/function convergence in species that are closely related (‘parallel evolution’) versus in species that are not closely related (‘convergent evolution’). However, this distinction is not always consistently made in biology and recently there have been proposals to use ‘convergent evolution’ as a general term [76]. We use the term in this general sense. Our proposal accounts for the present-day cross-linguistic similarity of huh?, but has to remain agnostic as to its ultimate origins – in the absence of historical language data it is impossible to tell whether the present-day forms go back to one ancestral form (a stabilising evolution scenario[77]) or whether they arose independently in different languages (an independent convergent evolution scenario [78]). In either case, the selective pressures are the same."

But the distinction between convergence and parallelism is not whether the lineages are closely related, but whether the trait (the word "huh") evolved from different traits or the same trait in the ancestor. That is, it would be parallel evolution if the ancestor language of English and Hindi had a word "bleeble" that meant "huh", and that word changed to "huh" independently in both English and Hindi. There's no evidence for this either! The authors admit that it "is impossible to tell" whether the word "huh" is in so many languages because it was present in the ancestor of those languages or not, but go on to use the term "convergent evolution" in their title. Harumph!

Mt. Etna is blowing smoke rings!

Mt. Etna, an active volcano on the island of Sicily, is blowing smoke rings! According to German volcanologist Dr. Tom Pfeiffer, the most recent paroxysm (violent eruption) changed the shape of the vents inside to allow circular rings to emerge.

Vulcan is taking a smoke break
Photo: Volcano discovery

This has apparently happened a few times before, including in 2000. Here's a video of a smoke ring from the 2000 event, taken by Geoff Mackley:

Volcanoes: sometimes they destroy your town, sometimes they chill out and blow a few smoke rings. I hope this has served as your daily reminder that you live on an amazing planet.