Archive for July 2010
If you’ve been on the internet at all in the past week, you’ve probably seen these lovely images from NASA, visualizing the height of tree canopies around the world. They’ve been on science sites along with art ones. In a sense, that alone is useful: using beautiful visuals to make people think about the world on a larger scale. But where did these data come from, and what do they really mean?
Why is it important?
The two main sources of anthropogenic influence of atmospheric carbon are (1) the burning of fossil fuels, releasing carbon dioxide into the air and (2) deforestation, removing trees which store large amounts of carbon. 20-50% of carbon in the atmosphere is currently not accounted for in climate models – a huge amount. Knowing where exactly this carbon is coming from is important for both conservation and making socioeconomic decisions regarding energy use.
Some scientists hypothesize that these unaccounted-for changes in carbon flux are due to poor knowledge of forest stands – both where deforestation has occurred, and where forests are recovering after previous deforestation. By knowing the size of forest stands, as larger trees can store more carbon, and keeping track of changes in the sizes of these stands, the hope is to have more accurate models for carbon storage and atmospheric carbon.
In the face of climate change, these kind of data are also useful, if updated over time, in seeing how rising temperatures and increased carbon dioxide affect tree growth (and thus carbon sequestration). Since plants get their carbon from the air, it seems natural that increased carbon dioxide would increase tree growth. Thus canopy height maps can help us to test this hypothesis.
From where did these data come?
Most of the data comes from work by Michael Lefsky et al. in a 2002 paper pubslihed in Global Ecology and Biogeography and a 2005 paper published in Geophysical Research Letters. In the 2002 paper, Lefsky and his team measured canopy height using LIDAR (Light Detection and Ranging technology), which essentially sends down a laser beam from which distance can be measured based on return time. LIDAR uses a shorter wavelength than typical radar, making it more sensitive to smaller objects such as particles in the air. Thus the name, Light Detection and Ranging. It also has a narrower beam than radar and thus is more specific in its measurements. In the paper, Lefsky and co. took LIDAR measurements on temperate forest stands and compared them with field measurements of forest height, finding that they matched up very closely. They also were able to do field measurements on the complexity of forest stands, meaning how much undergrowth lives beneath the canopy, and were able to create an accurate equation for predicting biomass of a forest stand based on LIDAR alone.
The 2005 study was another sort of proof-of-purpose paper, once again showing that LIDAR can predict above-ground biomass. The authors did not have complexity variables this time, but were still very accurate in their predictions.
For the beautiful figures of canopy height released by NASA, Lefsky combined his own data with that from NASA’s MODIS (Moderate Resolution Imaging Spectroradiometer), which is housed on a satellite and images the earth’s surface every 1-2 days. Combining the data on terrain from MODIS with his own canopy height data, Lefsky crafted these images over several years.
What does it mean?
Previously, large-scale vegetative modeling was only able to be measured in 1 km swaths of land, done by MODIS alone. Due to deforestation, there is a great deal of variation in canopy height on a smaller than 1 km scale – and finally we have the tools to create maps of forest canopy and thus help us better track carbon storage at these sites. The map isn’t perfect – it is a model after all – but it is far more accurate than anything we’ve seen yet. Expect interpretation from Lefsky and others in the near future.
But this isn’t the end.
As I mentioned earlier, traditional thinking assumes that forest growth will assist in carbon storage through increased growth due to higher carbon dioxide in the atmosphere. But a recent paper (July 21, 2010) in PLoS ONE by Lucas Silva (“silva” means forest in Latin, lollers), Madhur Anand, and Mark Leithead suggests otherwise.
A major tradeoff for growth in trees (as I’ve discussed elsewhere) is that the opening of leaf stomata (pores) to absorb carbon dioxide also causes water loss through evaporation from these same stomata. The authors of the PLoS paper looked at tree growth through tree rings and compared it with isotope analysis to measure water loss. If the trees they studied had increased growth due to increased carbon dioxide, they would also expect more water conservation, as more carbon dioxide would be able to enter the leaves without as much water loss.
Studying 4 species of tree at 4 forest types in Canada, they found a 53% increase in water use efficiency over the last century. (They looked at both young and old trees to account for varying growth rates and energy use.) This seems like good news – the trees are absorbing carbon dioxide more readily. However, they also saw a decline in growth overall. This suggests that other stresses, such as water, nutrients, and temperature, are limiting their growth despite the ease of access of carbon dioxide.
The next step: can we learn about tree growth from Lefsky’s maps? Are they accurate enough? It would be great to measure biogeochemical measures, such as water use efficiency, and compare this to large-scale forest size data. A girl can dream…
Okay, class: what have we learned?
Lasers are cool! The LIDAR technology, originally created for studying atmospheric chemistry, reapplied to study canopy heights has allowed us to visualize our forests in a new way. (And make some beautiful pictures.) There was a lot of work put into it – and to accurately measure how our forests are changing, increasing work will have to be done to keep the maps updated to create an index of canopy height on our planet.
However, we’ve also learned that we cannot necessarily rely on traditional hypotheses in times of climate change. While trees have the capacity to remove carbon from the atmosphere and store it, other factors can confound these effects, as we read in the PLoS ONE paper. While more work certainly needs to be done on this front (using large-scale climate measures for growth instead of dendrochronology, for example), their results are certainly sobering.
So, as usual, we need to do more work! We need to learn more! We have to challenge our hypotheses, and challenge new results that support or disprove them. It’s always easier when you have a mystery to solve: where is all that carbon anyway?
Cohen, W., Harmon, M., Wallin, D., & Fiorella, M. (1996). Two Decades of Carbon Flux from Forests of the Pacific Northwest BioScience, 46 (11) DOI: 10.2307/1312969
Lefsky, M., Cohen, W., Harding, D., Parker, G., Acker, S., & Gower, S. (2002). Lidar remote sensing of above-ground biomass in three biomes Global Ecology and Biogeography, 11 (5), 393-399 DOI: 10.1046/j.1466-822x.2002.00303.x
Lefsky, M., Harding, D., Keller, M., Cohen, W., Carabajal, C., Del Bom Espirito-Santo, F., Hunter, M., & de Oliveira, R. (2005). Estimates of forest canopy height and aboveground biomass using ICESat Geophysical Research Letters, 32 (22) DOI: 10.1029/2005GL023971
Running, S. (1999). A Global Terrestrial Monitoring Network Integrating Tower Fluxes, Flask Sampling, Ecosystem Modeling and EOS Satellite Data Remote Sensing of Environment, 70 (1), 108-127 DOI: 10.1016/S0034-4257(99)00061-9
Silva, L., Anand, M., & Leithead, M. (2010). Recent Widespread Tree Growth Decline Despite Increasing Atmospheric CO2 PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011543
As a preface, I should mention that I am a foul creature. I’m not really any more filthy than the rest of you scum – I shower almost every day! – but I am obsessed with my own filth. This obsession manifests itself in different ways. For example, I regularly take note of how much trash I create through sloth and excessive packaging, which could be beneficial in helping me reduce waste. Mostly it makes me feel like trash myself.
But it also shows up in perhaps strange ways. (I don’t typically think it strange, but my friends see it as an “eccentric” characteristic so maybe I am a huge weirdo.) For example, I use pore strips not to clean my pores, but rather to look at all the gunk that was stuck up there. “Gross! Cool! Look at all that stuff that was jammed into my face!” I am fascinated by all the body cleanse hoaxes (despite my knowledge that they don’t work), like ear candles vacuuming out earwax, because I would love to be able to visualize my own filth.
It also has led to a complete comfort with the various invisible creatures that inhabit my body. No, comfort is not a strong enough word: more like straight adoration. I love my microbes! I’m so proud of my parents for allowing me to eat so much dirt as a child! Carl Zimmer’s NYTimes article about the fecal transplant brought me great joy (paper here), and I’ve used it to amuse at endless dinner parties. (I go to dinner parties?)
And while the wild and wacky world of intestinal flora will always be cool, I often think about what is living on the outside of our bodies. We must have some flea or mite or otherwise crawler that lives on our skin. But how do I even find out that sort of information? (The google search for “human parasite” doesn’t work so well.)
When I was visiting friends in New Orleans in February, a tropical diseases student, Rebecca, called me over: “OMG Hannah, come here, I have to show you something, you’re going to LOVE IT!” (Shows a little bit about my reputation.) She proceeded to show me pictures of Demodex spp. To say I screamed and ran in circles with joy would be an understatement.
The first Demodex specimen was collected in 1841 from a human ear canal and was initially described as a tardigrade. (They both look pretty cuddly – you can see images here.) It was placed in its own genus in 1843 by Richard Owen, the same guy who brought us Archaeopteryx, the word “dinosaur” and the concept of homology. Demodex means “lard-boring worm.” How cute!!
Demodex includes 65 species, two of which inhabit human skin: D. folliculorum and D. brevis. The rest inhabit basically every other species of mammal: I saw literature on hedgehogs, alpacas, koalas, bears, along with the usual cats and dogs. They bury themselves head-down into a hair follicle, with their tails sticking up, and feed on dead skin and oils built up in your pores. That’s right, your pores. Infants rarely have Demodex specimens, but almost all elderly people have them. They are considered the most common human ectoparasite, and 50% of adults harbor these guys.
So on your face and in your hair you probably have a healthy population of crawly little mites! They can aggravate disease, but it hasn’t been proven that they actually cause any dermatological disorders. They mostly just clean up your face for you. But it will make you think differently when you borrow a friend’s pillow, or crash on a communal couch.
It is pretty weird to think that there is an organism that evolved to live on my face, lay its eggs in my pores, feed on my filth. Maybe I should be more careful next time I use pore strips, as to not dislodge any of my little friends.
I write this post going into science fiction as a fan, but also unaware of how most scientists think about it. I can imagine two central viewpoints: (1) scientists who enjoy it (like myself), simultaneously as entertainment and a bit of critical thinking and (2) scientists who dislike it due to its tendency to portray “evil scientists” and/or science and technology gone awry, destroying the world.
I didn’t really grow up reading science fiction. Sure, I was (and am) completely obsessed with some fantasy novels (e.g. Lord of the Rings) but never made the leap to becoming a true sci-fi nerd. It wasn’t until I started studying science more fully that I developed an interest in speculative science fiction. Many of the stories do deal with technology taking over civilization – but embedded within this framework is a great deal of excitement, along with some deserved anxiety.
The best way for me to explain these conflicting emotions is with an example of something that happened to me in the past few weeks. We are slowly inching closer to developing lab-produced organs, which would be incredibly beneficial for a lot of obvious reasons. Just this month there have been developments toward mass-produced red blood cells, as well as bioartificial lungs. Eerily, I read about these discoveries as I was tearing my way through Margaret Atwood’s Oryx and Crake, a speculative fiction novel about a bio-engineered future, including “pigoons” (pig/balloon) that have grown to massive sizes in order to grow 6 kidneys at a time for organ harvest, and “ChickieNobs,” a fast food product made from transgenic chickens that have no brains or beaks and grow 8 chicken breasts at once. While reading, I simultaneously was in wonderment about how we could be reaching the ability to actually engineer these creatures, but obviously nervous about the implications described in the novel. (No spoilers here!)
Some scientists might write this kind of anxious thinking off as trash. “We’re trying to develop organs to save lives – we don’t need a bunch of crazies trying to stop us in order to avoid a hypothetical bioengineering apocalypse!” But scientists are born and raised to be skeptical – and that’s all that much of this writing is. Being skeptical about the pure goodness of scientific advance.
But more importantly, science fiction is one of the ways that non-scientists absorb science. Oryx and Crake is a national bestseller, suggesting that millions of people have read her tale of bioengineering gone wrong. While we should assume that the public knows that this is in fact fiction and doesn’t take it entirely seriously, these stories do raise questions about the potential misuses of science that might not be as prevalent otherwise. I believe that scientists have a duty to communicate with the public (and not all agree with me on this). By knowing where non-scientists are coming from, scientists can better address some of the potential issues that might be raised by their achievements.
Sci-fi also provides a venue for discerning how our ways of thinking about science have developed historically. One of my favorite time periods for sci-fi is the 1950s: it was a time when just enough was known to speculate wildly, but not enough to fully disregard these speculations. After all, Watson and Crick did not discover the DNA structure until 1953! Thus you have the birth of many of our superheroes, variously mutated by “cosmic rays” or radiation, altering their molecular structures and giving them superpowers. We had just enough pieces to wonder, but not enough to know the full picture.
And sometimes the stories told ended up being truths nowadays. Reading stories that feature scientific dreams of these writers, and now knowing that they’ve come true, can be heart-wrenching. In one of my favorite short stories, “The End of the Beginning” in R is for Rocket, Ray Bradbury describes a couple gripping their seats with excitement and nervousness as their son boards a shuttle – the first shuttle to land on the moon. This collection was written in 1965, 4 years before Apollo 11 landed on the moon. Bradbury’s description is incredible:
All I know is it’s really the end of the beginning. The Stone Age, Bronze Age, Iron Age; from now on we’ll lump all those together under one big name for when we walked on Earth… Millions of years we fought gravity. When we were amoebas and fish we struggled to get out of the sea without gravity crushing us. Once safe on the shore we fought to stand upright without gravity breaking our new invention, the spine, tried to walk without stumbling, run without falling. A billion years Gravity kept us home… That’s what’s so really big about tonight … it’s the end of old man Gravity and the age we’ll remember him by, once and for all.
Gives you shivers, eh? Of course, this day has come and gone in real time. We are still constrained by gravity, we haven’t set foot on a planet beyond the moon. But these science fiction stories can bring us back to that time of wonderment, help us to experience a feeling we missed: the great excitement of space potentially conquered. And although it didn’t happen quite the way Bradbury described it, we can pretend for at least a little while.
Science is about that excitement. About that drive to discovery, about idealism and hope. It’s easy to forget that, working away at my lab bench, pipetting DNA into tubes. Now we know a little more about science – enough that we no longer dream of mutated superheroes. But we still dream about the day when we’ll make our big discovery, solve our own scientific problem.
Science fiction can remind us of this wonderment and hope. But it also sends us a warning – to think about the potential implications of our findings, beyond our idealistic dreams. While those implications might not be as exciting as a science fiction novel, they exist, and scientists should be aware of them.
With that, I’ll leave you this quote from David Brin from Nature‘s series of interviews with science writers this past winter.
Science fiction is badly named — it should have been called speculative history… Whether you are in a parallel reality or exploring the future, it is all about the implications of change on human lives. The fundamental premise of sci-fi is not spaceships and lasers — it’s that children can learn from the mistakes of their parents.
Dimethylsulfide. Does that word mean anything to you? “Why yes,” you organic chemistry nerds may say, “It clearly is a molecule of sulfur with two methyl groups attached.” That’s as far as I could have gotten – until this past week, when I inundated myself with information on dimethylsulfide (DMS) due to a paper published in Science. Now I’m enlightened – what a wonderful molecule! Let me spoil it for you: it is simultaneously a defense mechanism, a chemical cue pervasive throughout the marine food web, and an effector on the earth’s climate. (See illustration at bottom of post for summary.) That’s right. Just a sulfur molecule with two methyl groups attached. Now let’s back up a bit.
DMS is a sulfur compound that accounts for 50-60% of the total natural reduced sulfur flux to the atmosphere (even more than either volcanoes or vegetation). While sulfur in the atmosphere can cause acid rain, it is also very important, as it helps form clouds. In order for water to transition from a gas to liquid in the atmosphere, it needs a small particle in the air to adhere onto, known as a cloud condensation nucleus. Sulfur oxide, which can be derived from DMS, is one of these particles. Clouds not only carry our precipitation, but help to reflect sunlight (and thus heat) back into space, affecting our planet’s climate.
After the realization of its importance as a cloud condensation nucleus, scientists began to look for DMS’s planetary source and found that 95% of the atmospheric DMS originates in the oceans – but from where? As illustrated in my figure, it is actually formed in certain species of phytoplankton and released when cells leak, most often due to herbivory by other organisms. The phytoplankton itself actually makes a molecule called DMSP (dimethylsuphoniopropionate, if you must know). When its cell wall begins to break down, stores of DMSP (from an unknown location within the cell) and an enzyme, DMSP-lyase, are released into the surrounding water. This DMSP-lyase removes the P-group, leaving us with our favorite molecule of the day, DMS.
In 1987, the CLAW hypothesis (named for its authors) was put forward by James Lovelock and a handful of his lackeys to support his infamous Gaia hypothesis which suggests that microorganisms regulate the Earth’s climate to maintain conditions suitable for life. CLAW hypothesized that levels of DMSP and its P-cleaving enzyme in phytoplankton are regulated by light and temperature, with greater amounts of DMSP produced when it gets warm in order to send more DMS into the atmosphere, deflecting sunlight and reducing global temperatures. However, like most support for the Gaia hypothesis, this idea requires that phytoplankton act altruistically, releasing the DMS for the good of the planet, which does not make much sense in light of natural selection. (A good review of this and the above sections can be found in this paper by Rafel Simo.)
A 2001 MEPS paper by Kathryn Van Alstyne and others provides evidence that the release of DMSP and DMSP-lyase by phytoplankton is actually a chemical defense mechanism. After DMSP-lyase activity, the resulting products are DMS and acrylase or acrylic acid. The authors found that acrylic acid deterred grazing by two species of sea urchins on algae, and they suggest that this is due to an aversion to acidity by the urchin itself or that the acid irritates its gut microbes. While the evidence is not directly causative, as the authors showed a reaction to acrylic acid and not to DMSP-produced acrylic acid in vivo, it does suggest (with other evidence) that the important part of this reaction to the phytoplankton is not DMS, but rather its byproduct.
Smaller grazers, such as isopods, had no reaction to the acrylic acid in that paper. But a paper published in Science this week (July 16 2010) by Justin Seymour, Rafel Simo, and others looks into the effects of DMSP on the smallest grazers: microbes. Using “microfluid technology” (see details at end of post), the researchers measured the strength of attraction of 4 different types of microbes (7 species) to varying concentrations of DMSP, DMS, DMSO (dimethylsulfoxide, a DMS and DMSP degradation product), GBT (glycine betaine, a molecule analogous to DMSP in structure and function), and artificial seawater (as a control).
- Each of the 3 species of autotrophic plankton reacted differently to DMSP in the water. The algae Micromonas pusilla showed strong attraction to DMSP, taking it up presumably as a carbon and sulfur source. The cyanobacterium Synechococcus sp. showed no reaction. Most strangely, the algae Dunaliella tertiolecta moved very strongly toward DMSP, but not to assimilate it directly; rather, it cleaved the molecule into DMS extracellularly and potentially assimilated that molecule instead. The authors do not know why this action occurs.
- Two species of bacteria, Pseudoalteromonas haloplanktis and Silicibacter sp., each moved toward the DMSP for assimilation as part of their carbon and sulfur requirements.
- Two consumers, one a herbivore to eat the algae itself (Oxyrrhis marina) and the other a bacteriovore which strove to eat the bacteria consuming the DMSP, each showed positive chemotaxis and moved toward the DMSP source.
This last part is the most interesting: these two microbe species use the DMSP as a chemical signal that there is food around. Out of all the molecules that could leak from the burst cell and indicate prey, it is this very molecule, DMSP, that does the trick.
But wait: didn’t the 2001 paper I just wrote about suggest that DMSP is a chemical defense of phytoplankton? What is it doing drawing in its own predators? The authors suggest that previous studies have flawed experimental design, releasing far too much bulk DMSP into the environment in contrast to their own “microfluid technology.” Previous studies, such as a 1997 Nature paper by Gordon Wolfe and a 2003 paper by Suzanne Strom, found that O. marina has a higher tolerance to digesting DMSP and is less repelled than other species. More work should be done in order to get to the root of this contradiction.
Thus far, we have DMSP attracting bacteria to consume the DMSP itself, drawing in an herbivore to consume the DMSP-producer, and a bacteriovore attracted to the DMSP in order to find its own bacterial prey. This is not the end of the story, as DMSP is a prey indicator at higher trophic levels as well. A 2008 Science paper out of UC-Davis and UNC found that planktivorous fish use DMSP as a foraging cue, aggregating near DMSP hotspots. Furthermore, Gabrielle Nevitt reviewed literature in 2008 on seabirds (Order: Procellariiformes) using DMS as an olfactory cue to identify patches of its own prey, fish and squid, feeding on the zooplankton and its phytoplankton prey. A similar pattern has also been found in seals and whale sharks.
The evolutionary implications of this are astounding. It seems as though many molecules released from a leaky phytoplankton cell could be used as indicators of these clusters of consumption. However, DMSP has something special: sulfur. We all know that smell, and perhaps it is this stinkiness that has allowed it to become such a pervasive indicator throughout the marine food web. In her review, Nevitt discusses the evolution of DMS-sensitivity in seabirds, and using phylogenetic trees, shows that only the species that are reared in dark burrows, relying on smell alone to identify food, currently have DMS-sensitivity. How did this apparent convergent evolution occur? Is it convergent? (I have no answers to these questions.)
Are there any implications for climate in these findings, as DMSP is indirectly responsible for increased albedo (sunlight reflection) in our atmosphere? I doubt that there are any direct consequences that we can enumerate. As all biogeochemists know, the stuff of the air frequently comes from the stuff we live on and in: soil and water. This is simply another tie to the way microbes and abiotic stuffs relate to climate-regulating molecules. The authors of this week’s Science paper note that “microbial behaviors, played out over microscale chemical landscapes, shape planktonic food webs while potentially influencing climate at global scales.” DMS as a prey cue should create a positive feedback loop, drawing more herbivores to open more cells and leak increasing DMSP, which in turn draws more herbivores. Some studies show varying ties of DMSP production to species, light, temperature and salinity (review by Stefels et al. here), but it seems to me that the DMS-as-prey-cue and DMS-as-climate-regulator processes are unlinked, so would not work together in any predictable way.
If you take nothing away, take this: sometimes the universe is more connected than we can imagine.
(Sidenote: should I give up strict science and become a science illustrator?)
NOTES ON MICROFLUID TECHNOLOGY:
The idea behind this technique is that microbes inhabit a “dynamic and patchy nutrient landscape” in which nutrient levels vary over micrometer scales. The microfluidic device is a chamber designed with the “objective of creating a diffusing band of chemoattractant, to simulate an ephemeral, microscale nutrient patch.” There is a chamber in the center into which fluorescence-labeled chemoattractant is added to the desired concentration, and then input is cut off. Thus the chemical will dissipate slowly through the closed chamber, trying to imitate the open ocean. The researchers then add their microorganisms, and measure their distribution and the distribution of the fluorescent chemical. This allows the researchers to track the intensity and location of the chemical, as well as the behavior of single organisms.
This information is from a paper in Limnology and Oceanography: Methods by J.R. Seymour, T. Ahmed, and R. Stocker entitled “A microfluidic chemotaxis assay to study microbial behavior in diffusing nutrient patches” (2008: 6 (477-488)). A pdf copy of this paper is available on Roman Stocker’s webpage, here (pdf warning!).
Here’s a picture of the device, thanks to Roman Stocker. The blue tube is the microbe input, the green tube is chemical input, and the red tube is for drawing out waste. It sits on top of a microscope.
DeBose, J., Lema, S., & Nevitt, G. (2008). Dimethylsulfoniopropionate as a Foraging Cue for Reef Fishes Science, 319 (5868), 1356-1356 DOI: 10.1126/science.1151109
Nevitt, G. (2008). Sensory ecology on the high seas: the odor world of the procellariiform seabirds Journal of Experimental Biology, 211 (11), 1706-1713 DOI: 10.1242/jeb.015412
Seymour, J., Simo, R., Ahmed, T., & Stocker, R. (2010). Chemoattraction to Dimethylsulfoniopropionate Throughout the Marine Microbial Food Web Science, 329 (5989), 342-345 DOI: 10.1126/science.1188418
Simó, R. (2001). Production of atmospheric sulfur by oceanic plankton: biogeochemical, ecological and evolutionary links Trends in Ecology & Evolution, 16 (6), 287-294 DOI: 10.1016/S0169-5347(01)02152-8
Stefels, J., Steinke, M., Turner, S., Malin, G., & Belviso, S. (2007). Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS) and implications for ecosystem modelling Biogeochemistry, 83 (1-3), 245-275 DOI: 10.1007/s10533-007-9091-5
Van Alstyne, K., Wolfe, G., Freidenburg, T., Neill, A., & Hicken, C. (2001). Activated defense systems in marine macroalgae: evidence for an ecological role for DMSP cleavage Marine Ecology Progress Series, 213, 53-65 DOI: 10.3354/meps213053
G. V. Wolfe, M. Steinke, & G. O. Kirst (1997). Grazing-activated chemical defence in a unicellular marine alga Nature, 387, 894-897
Hey, all! Welcome to the 25th edition of the Carnival of Evolution. I’m honored to get to host the carnival this month – and, as you’ll see, I’ve got a lot of great posts to share. So grab some cotton candy, wander around, and stop to try the rides and exhibits I’ve organized (and illustrated) for you from 21 fabulous blogs.
There were several interesting posts this month about symbiosis – long-term interactions between two different species for the benefit of at least one.
Labrat explains the genomic changes that take place when a bacteria forms a symbiotic relationship with a eukaryotic cell – that’s right, it doesn’t only lose its “free will” (whatever that is), but also part of its genome. Read her post to find out how and why!
In contrast to Labrat’s harmonic story of mutual symbiosis, Psiwavefunction tells a grand story of intrigue, karma, and theft. (The jokes are all her’s.) Over at Skeptic Wonder (one of my new favorite blogs), you can read the saga starring a cryptophyte, a ciliate and a dinoflagellate. Seriously: head over and read the whole fascinating (and hilarious) post yourself.
Corals are well-known symbionts: they are inhabited by zooxanthellae, which undergo photosynthesis and produce energy for the coral in exchange for comfort. I usually think of corals as colonial organisms, living together in large groups in reefs. However, this is not always the case, as Lucas Brouwers explains in his Research Blogging Editors’ Selection at Thoughtomics on how solitary corals evolved.
As we know, the process of evolution takes an incredibly long time. How do evolutionary biologists study the process of natural selection just in their lifetimes? Two posts this month feature experimental methods to test traditional theories of natural selection.
At Denim and Tweed, Jeremy Yoder wrote about an experiment testing density compensation: the observation that islands have fewer species but a greater density of each species. By netting off or introducing predators to small islands, the scientists were able to draw conclusions about whether competition or predation was a more important factor in the natural selection of anoles.
In a similar vein, Marc Cadotte of The EEB and Flow wrote about Darwin’s naturalization hypothesis, which posits that the struggle for survival is most severe between closely related species. Thus, species introduced to an ecosystem are more likely to thrive if they did not share a common ancestor recently. He explains a recent experiment using bacteria species of varying “closeness” (i.e. phylogenetic distance) in variable communities.
Mimicry in the natural world is usually easily explained by natural selection. For example, if predators recognize the coloring of a poisonous organism and avoid it, genes coding a similar pattern will be selected for in a non-poisonous organism due to its release from predation. But sometimes we observe mimicry even where the distributions of the two organisms do not overlap. At NeuroDojo, Zen Faulkes provides some potential reasons why these “mimics without models” exist.
We humans often like to think of ourselves as free from the processes of evolution. And although selective pressures have been reduced in some parts of the world, natural selection is still at work. (My high school biology teacher told me that C-sections are currently relaxing selection against bigger heads – but don’t cite me on that.) At Why Evolution is True, Jerry Coyne wrote about a recent article supporting the current selection of the EPAS1 gene in humans living at high altitudes.
Here at Culturing Science this month, I wrote about the global distribution of microbial species in the face of the traditional idea that, due to mechanisms for wide dispersal and vast numbers, in the microbial world “everything is everywhere.” But if all microbes are everywhere at all times, waiting for the right conditions for their success, are they affected by selection pressures?
The growing and controversial field of social evolution tries to explain why we evolved social behaviors, many of which initially seem against our benefit. It’s particularly interesting when features we commonly attribute as unique to humans – such as empathy, morality, or culture – are found where we don’t expect them.
Let’s take empathy, for starters. It’s often assumed that humans alone are capable of empathy, since an awareness of others and ourselves (a.k.a. consciousness) is necessary to make the kinds of comparisons and conclusions to feel another’s pain. At Living the Scientific Life, GrrlScientist reviews an interesting study about empathy in crows, which console one another after a fight. After I get into a fight, I know that all I want is someone to preen my feathers!
Similar to empathy, adoption is something we think of as unique to humans. After all, why would a creature interested in the spread of its own genes take care of another? At This Week In Evolution, R. Ford Dennison discusses a paper on adoption in red squirrels, weighing the risks of taking on an additional baby with the relatedness of the orphan to the adoptive mother.
Many arguments in the field of social biology seem to be based on differing definitions of terms: what is empathy? morality? culture? Over at Biotunes, Dr. Henneman discusses a recent finding that human babies have a grasp of morality, although it has been traditionally taught that morality, an idea too abstract for a child, is something taught by parents and culture over time.
Additionally, a recent finding that chimpanzees are affected by their social culture was contested by French anthropologist Dan Sperber. At The Primate Diaries, Eric Johnson goes through the definitions of culture proposed by each side, and concludes that Sperber’s problem is not in the methodology, but rather “his objection comes from the definition of culture that he prefers.”
At The Thoughtful Animal, Jason Goldman writes about how sexual preferences affect brain size in his hilariously entitled post “Polygamous Males Have Larger… Hippocampi!” It’s a really lovely study: the scientists studied two populations of very closely related voles (within the same genus), one of which has polygamous males while the other has monogamous. Presumably a polygamous male, requiring a larger home range (to meet many lucky ladies) would need a bigger brain to store the information. Is it true? Click here to find out
Zen Faulkes wrote up a study at NeuroDojo about … well … cricket sex! The scientists were very dedicated to this topic: they set up 2 video cameras for 2 summers in a row capturing all the activity of 200 or so crickets. And then they watched the footage. After all that hard work, they deserve to have their findings known – so go ahead, read it.
Over at 360 Skeptic, you can read a tale by Andrew Bernardin about testosterone in dark-eyed juncos, those cute little winter birds found on the East Coast of the USA. While testosterone in birds can increase mating success through increased territory defense and mating displays, the authors wanted to know if there is such thing as too much testosterone. Maybe that’s why I’ve never seen a really jacked junco…
In a lovely post on Evolving Thoughts, John Wilkins goes through the arguments for different definitions for the word “homology.” He argues that “homology” does not necessarily refer to common descent (although that’s how it is often used), but rather simply to a part of one organism “agreeing” with a part of another organism, with no explanation built in. In the process, he goes through the history of cladistics in perfect detail (with some beautiful illustrations to boot).
You know how I feel about cephalopods – so I was very excited to get a submission from Cephalove on the evolution of octopus brains. In order to assess the evolution of the nervous system generally, Mike Lisieski takes us a few steps back to our closest common ancestor with octopuses: the Urbilaterian (or “original bilaterian”). He suggests that to learn about neural evolution generally, we should look at how cephalopod and human brains evolved separately from this common ancestor.
At Byte Size Biology, Iddo Friedberg explains the beautiful paper comparing the genomic makeup of E. coli and the operating system Linux, revealing how evolved and created systems differ. Does this put us a step closer to developing cyborgs?
The finding that we Homo sapiens share genes with Neanderthals and possibly bred with them was big news this month – and, over at The Atavism, David Winter does a great job explicating some of the issues that have been brought up. Just because we interbred does not mean we are the same species as Neanderthals; but it does bring up some issues of how we define a species. (Ahh, the species problem, one of my favorite things to think about…)
At The Voltage Gate, Jeremy Bruno wrote up some research on the biogeography on Flores, where the famous small fossils of Homo floresiensis were found. (“A hobbit’s contemporaries,” in Jeremy’s words.) The authors compared the distribution of other species on the island of Flores to that of other islands to see if similar patterns of evolution occurred, and ultimately to draw conclusions about the size of H. floresiensis. A great read.
Jason Goldman takes a look at risk-taking in primates, and whether it is related to foraging strategy at The Thoughtful Animal. The study looked at bonobos, which will chance upon an abundant food source and gorge, and chimpanzees, which are constantly gathering smaller foods. Which one is more likely to take a gamble on its snack quantity?
Over at Pleiotropy, Bjorn reports on the discovery of a fossils of multi-cellular precursors older than we’ve ever found, pushing back the evolution of multicellularity back 200 million years. These fossils do not represent specialized structures as we normally think of metazoans – but there is evident of cell-to-cell signaling, suggesting that these guys are not simply bacterial colonies.
Everything you ever wanted to know about tunicates – seriously! Check out this great, informative post at Fins to Feet, describing how vertebrate life may have evolved from these sessile sponge-like organisms. The answer lies in their larval form, which has a notochord. Through the process of neotony (which Lucas also discusses in his coral evolution post), when an organism continues to exist in its larval form into adulthood, these larvae could have evolved into early vertebrates. Check out the whole post here.
Evolution Shop Talk
Two posts this month try to clear up common mistakes or assumptions made about evolution. At Darwin’s Bulldogs, Madhusudan Katti writes about the common misconception of an “evolutionary ladder.” “EVOLUTION IS NOT A LADDER” is his battle cry; there are no pinnacles is his argument. Similarly, Andrew Bernardin at 360 Degree Skeptic responds to wording in a paper implying purpose in evolution. He explains that there is no goal in evolution, and more complex does not mean better or more evolved.
Some bloggers tried to debunk creationists this month. At Evolution is True, Jerry Coyne criticized a group that tried to reconcile evolution with the Adam and Eve story, and over at Pleiotrophy, Bjorn explains why some creationist promotional material he received is not truth in two parts: II and III.
Thanks for stopping by, and I hope you enjoyed the Carnival of Evolution. Next month will be hosted by Jason Goldman at the Thoughtful Animal. So write up your blog posts about evolution, and submit them here by August 1, 2010.