Mangrove Evolution and Plate Tectonics

More Mangrove madness for May, I guess! Anyway, my previous post about some of the nifty mangroves I'd seen down in the Everglades got me thinkin': what's the evolutionary history of mangroves? Turns out, that's kind of a tricky topic, and one that ends up incorporating a lot of interesting taxonomic, ecological, botanical, and paleobotanical perspectives; as a for-instance, it requires that you make some clear definitions regarding what you mean by "mangrove". In one sense, you can talk about the taxonomic group of fruiting plants that we call "Mangroves" (which includes a lot of ~22 families). HOWEVER, in another sense, we can talk about the ECOLOGICAL niche of "mangroves", i.e., coastal swamps that develop as a result of biologically-mediated factors. A future post will explore those topics in more detail.

THIS post, however, is going to focus on some slick work (in my opinion) that has been done linking mangroves (including genetics AND fossils) with the geological factors that influenced their evolutionary history.

Workers with interests in mangroves have long recognized an interesting pattern in modern mangrove (taxonomically-defined) biogeography, namely that Mangrove species richness declines dramatically from a peak in the West Pacific to a minimum in the Caribbean/West Atlantic Zone. The figure below is from Ellison et al. (1999) that shows this pattern diagrammatically.

There are two explanations that have been put forth to explain this pattern. Originally, mangrove biogeography was explained in the context of an Indonesia/West Pacific "Center of Origin" distribution (Duke, 1995). In otherwords, mangrove taxa originated in one spot, and then subsequently disperesed globally. This is easily the oldest explanation for this observed pattern of diversity, and goes back into the literature for ~100 years.

After the plate tectonic revolution, however, another explanation presented itself: namely, that mangrove taxa evolved around the Tethys seaway in the late Cretaceous, and regional diversity is the result of diversification and evolution in the context of plate tectonics and the movement of continents (Ellison et al., 1999). This has been termed the "vicariance hypothesis", and is the big focus of the paper by Ellison et al. (1999).

Ellison et al. (1999) explore several lines of evidence as a means of testing the validity of one or the other hypotheses, and frankly, I think they're rather clever: FIRST, they take a look at the paleobiogeography of fossil mangroves (pollen or macrofossils) and compare that to modern biogeographic patterns. Ellison et al. (1999) compile a substantial list of fossil mangrove occurrence, and demonstrate that, actually, the fossil record is pretty damn good! The figure below is from Ellison et al. (1999; their figure 2), and shows generalized maps of mangrove occurrence through time.

Importantly, on the basis of their fossil mangrove occurrence database, Ellison et al. (1999) report that, statistically, there isn't any significant correlation between mangrove species-area occurrences and distance from the Indonesian/West Pacific region throughout the Tertiary. What is demonstrated, however, is that mangrove fossil occurrence shows a relativly wide-spread distribution of different mangrove taxa along the ancient Tethyan shoreline. Ellison et al. (1999) recognize that this conclusion provides testable hypotheses for relating other strongly correlated ecological aspects of mangrove environments.

This conclusion leads to their SECOND approach to interrogating mangroves....SNAILS. Turns out, mangroves have some pretty conservative associations with different gastropod taxa; in otherwords, the specific ecology and environmental stresses associated with Mangroves has also resulted in snail populations that almost always co-occur. Cooly, Ellison et al (1999) compile a fossil-occurrence database of gastropods, and compare that distribution to their fossil mangrove database! Neat, huh? Their results are shown below, in their Figure 3:

They proceed to explore ecological "nestedness" of gastropods and mangroves through time, and do some pretty nifty statistical manipulations of the data to test whether mangroves, their gastropods, and the species-area relationships can be associated with a "center-of-origin". Ellison et al. (1999) conclude that, on the basis of the fossil distributions of both mangroves, gastropods, and the patterns of their species-area relationships, that a probable Tethyan origin, and then subsequent diversification patterns are related to tectonic reconfiguration of shorelines and continents. Neat, huh!

It's a pretty neat use of both modern biogeographic patterns as well as ancient data, and it makes me wonder what other possible insights could be mined from both this and other settings? For instance, is there anything we could learn about large-scale paleo-oceanographic circulation patterns from these paleobotanical collections? Can we see other ecosystems being strongly influenced by tectonics in this way? Can we take the fossil record of mangroves, tie it to associated mangrove-dominated depositional environments, and see any statistical patterns in stratigraphic occurrence, mangrove biogeography, and tethyan tectonics? Or how expanding out from the "taxonomic" mangroves into the "ecologic" mangroves, which have a (potentially) older fossil record? Are there any statistical patterns to be elucidated from those occurrences? Who knows!?

Regardless, mangroves are obviously pretty amazing plants, but also seem to have a geological story to tell us as well! Maybe it's time us rock-o-centric types start really thinking about some of the critter-o-centric fields, and how one can inform the other in new and exciting ways.

WORKS CITED:

Duke, N.C., 1995, Genetic diversity, distributional barriers and rafting continents - more thoughts on the evolution of mangroves: Hydrobiologia, v. 295, p. 167-181.

Ellison, A.M., Farnsworth, E.J., and Merkt, R.E., 1999, Origins of mangrove ecosystems and the mangrove biodiversity anomaly: Global Ecology and Biogeography, v. 8, p. 95-115.

Modern Mangroves

Just a brief picture-y related post, as I try and rise above the clinging busy-ness of the end-o'-the-semester. I was lucky enough to head down to South Florida over the spring break (in late March), and in addition to eating all sorts of delicious shell fish and exotic fruits (sapote! sapodilla!) I also had the chance to see some pretty rad mangroves swamps!

Mangroves, of course, are the utterly kick-ass salinity-tolerating plants that form impressively dense coastal swamps along tropical shorelines. Because they live in environments that are, traditionally, so hostile to plants, these awesome trees have evolved some pretty slick adaptations. They can excrete excess salt from their roots and leaves, which is pretty awesome, and can similarly limit water loss during low-tide exposures. And, from a sedimentological view point, they are also completely amazing sediment baffles, effective at dissipating incoming wave energy and trapping any entrained sediment. Neat-o!

Anyway, the picture below is from Florida bay, and just shows some isolated red mangroves growing out in the shallows. When we came back and mucked around in the mud after low tide, the WHOLE area was just covered in horseshoe crab traces going everywhere (no pictures, sadly...). In the background on the right, you can JUST make out the distopian hellscape that is Miami.

This next picture is from the Everglades, and shows some more Red Mangroves growing along the edge of the brackish water Coot Bay, and were taken as we canoed around the backwaters. Notice the oysters encrusting the mangrove limbs! Neat!

Here's another oyster and mangrove shot!

And, finally, here's some mangrove pneumatophores exposed along the canal access to Coots Bay.

Pretty amazing plants!

The Importance of Stupidity in Research

Here's a brief essay by Martin Schwartz, published in the Journal of Cell Science. The title really says it all: The Importance of Stupidity in Scientific Research. There's not much more that I can say, except that I think Dr. Schwartz pretty much hits it right on the head with this one! It's a short, one-page essay about the importance of recognizing the human-ness of science and cultivating and fostering the proper attitude towards uncertainty and the unknown in research. Pretty good stuff, with lots of good advice for both Teachers and Students.

Works Cited:

Schwartz, M.A., 2008, The importance of stupidity in scientific research: Journal of Cell Science, v. 121, p. 1771

Non-Newtonian Pool Party!

Yet more crazy YouTube videos of weird, geologically relevant stuff! This time...it's non-newtonian fluids!

Newtonian fluids are the sort of everyday, hum-drum fluids we generally interact with (like coffee, or beer). If you exert some force over area on a newtonian fluid, it deforms pretty much instantly in proportion to the force applied to it. Another way of saying this is that newtonian fluids have a constant viscosity.

BUT non-newtonain fluids have a variable viscosity; generally, this viscosity varies nonlinearly as a function of either the amount of shear stress (force over an area) applied OR as a time-dependant function. Examples of non-newtonian fluids include things like ketchup (which gets stuck in the bottle until you shake it; the sudden application of force to the ketchup drastically reduces the viscosity, letting it flow out of the bottle) and whipped cream (which experiences an increase in its viscosity as a function of applied shear stress).

If you are lucky enough to be a geologist, then you actually have more opportunities than most to interact with non-newtonian fluids. Drilling muds and clays, used to lubricate drill bits, are examples of non-newtonian fluids. Even cooler, of course, are things like debris flows, which behave as viscous, non-newtonian fluids.

You can make your own shear-thickening non-newtonian fluid right at home, by mixing ~2 parts corn starch with 1 part water; get it good and gloppy, and you've got a fluid that, when you gently push against it, behaves just like water, but when you smack it hard, it behaves more like plastic. Try it out! It's insanely fun!

And, if you are really ambitious, you can fill up a whole giant tub of the stuff, and run across it, like these nuts did (the whole video is in Spanish, so that's a little tricky; still, it's fun!):



AND, just for more fun: here's a video of some of the "do-it-yourself home-made cornstarch non-newtonian fluid", put on a speaker!

Darwin and Earthquakes, on CNN

I found an interesting little article on CNN's website today: it's a brief write-up of Darwin's own Chilean earthquake experience in 1835, with some excerpts from The Voyage of the Beagle, including his musings on geology, rates, and processes. The piece is written by a historian of science, John van Wyhe, and reiterates that the Earth, just like Darwin observed and recognized, is a dynamic system.

You can read the article here.

Time-lapse video from underneath a glacier

How's this for rad:



Pretty slick, huh? It's a clip from some NOVA Special on PBS. Just a neat video to help you make it through the afternoon!

The Saddest Trace Fossil In The World

Trace fossils are great sedimentological tools; they can tell us a lot about the local energy conditions, instantaneous sedimentation styles, and substrate conditions, and tend to be controlled by traditionally hard-to-figure-out paleoenvironmental proxies like salinity, light, and nutrient availability. So, seds-oriented folks trying to get some really detailed info about depositional environments tend to go crazy over these arcane little scratches, tubes, and trails found in the rock record.

However, if you're one of the paleontologically oriented sorts, then I reckon trace fossils must be really aggravating, form a biological perspective at least. Oh, sure, you can get some morphological detail out of them, and narrow down the sort of critter that made them, but don't you just hate how damn COY those little fossils are about the trace-maker's REAL identity?

In a few lucky cases, though, the sedimentary record has conspired to give us little glimpses of the tracemakers identity. But man! It's just so sad, isn't it:


The picture above is of the Jurassic Horseshoe crab Mesolimulus walchi, from Germany, along with its very own preserved trail (probably of the ichnogenus Kouphichnium, but I might be wrong). I took these pictures at the AMNH a couple of years ago...and it was under weird museum mood-lighting, so it was a little darker than optimal for picture taking.


Anyway, this poor little fellow was just tooling along the anoxic bottom, trying to find some oxygen, I reckon, when he just gave up the ghost. I mean, look at him there, and the end of his trail, forever entombed in sediment!


The pathos!

Darwin - The Rock Opera

Jumpin' Cats! Check it out: Some Swedish band has put together a rock opera based on Charles Darwin's life and work. AND you can stream it live, off that there internet! The masterpiece is called "Tomorrow, in a Year", and includes tracks titled "Geology", "Epochs", and "Letter to Henslow"...how badass is that!?

Geology and Beer

Despite what those wine-swilling elitist bastards would have you think, the REAL drink of geologists everywhere is BEER. I have a favorite half-remembered quote from some Victorian mountaineer/geologists who said, to the effect, "Beer never tastes so good as after a hard day of field work". Of course, my apocryphal quote speaks Truth: beer, in the field, after a day of measuring section, or mapping, or tromping up and down hill and valley lugging samples, is something to bring a smile to even the most grizzled of geologists.

Anyway, folks might have seen this before, but it bears repeating. Why Geologists Love Beer is an article from Wired, based around beer-drinking culture and the most recent AGU Meeting in San Fransisco. There's even a little video to watch, but be warned: it'll make you thirsty.

Happy Darwin Day!

Happy Darwin Day, everybody! Celebrate the day by punching a creationists and (if you can) maybe enjoy a little differential reproductive success, you know what I mean, wink wink wink.

Also, here's a link from The Victorian Web with an online edition of Richard Owen's anonymously written "Critique of Darwin's Origin of the Species"; it's an interesting read, mainly on account of it PRETTY much making all the exact same arguments that stupid creationists make today...they just don't learn!

Oh well! Happy Darwin Day!