Complex amphibian responses to past climate change

Eastern tiger salamander: Ambystoma tigrinum, courtesy of Wikimedia Commons

We were like gophers, but now we’re like voles

Timeline, 2005: There is a cave in Yellowstone packed with fossils from the late Holocene, from about 3000 years ago. We can glean from this trove of stony bone how different taxa respond to climate change at the morphological and genetic levels and define and make predictions about the current response of the world to such changes.

The cave, which is in a sensitive area of the park off limits to visitors, houses the fossilized bones of rodents, wolves, amphibians, bears, coyotes, beavers, and elk, among others. This fossil cornucopia has yielded so much in the way of stony evidence that sorting it all is in itself a mammoth task. But two climatic stories have emerged from the samples it has yielded.

A global warming story…from the Middle Ages

The first story is about salamanders and climate change. No, it’s not a 21st-century story about global warming, but a Middle Ages story about a hotter planet. From about 1150 to 650 years ago, the earth underwent a brief warming period known as the Medieval Warming Period. During this time, the sea surface temperature was about a degree warmer and overall, the planet was much drier. This climatic anomaly was followed by what many climatologists call the Little Ice Age, a period that ended around 1900.

During the warm and dry period, animals in what would become Yellowstone National Park responded in ways that left clues about how animals may respond today to our warming planet. Amphibians make particularly sensitive sentinels of environmental change, alerting us to the presence of pollutants or other alterations that affect them before larger manifestations are detectable. And they even provide us evidence in their fossils.

Hot times, smaller paedomorphic salamanders

A group from Stanford excavated the fossils of Ambystoma tigrinum (the tiger salamander) from 15 layers at the Yellowstone site and divided them into five time periods based on their estimated age. They then divided the fossils again based on whether they represented the tiger salamander in its larval, paedomorphic, early adult, or later adult stages. The tiger salamander exhibits paedomorphism, in which the animal achieves reproductive capacity or adulthood while still retaining juvenile characteristics. In the case of the tiger salamander, this translates into remaining in the water, rather than becoming a terrestrial adult, and into retaining characteristics like frilly gills. The molecular determinant of whether or not an amphibian undergoes complete metamorphosis from juvenile to adult is thyroid hormone; when levels of this internal signal are low, the animal will remain juvenile.

The researchers found that during the medieval warming period, the paedomorphic salamanders became smaller than they were during cooler times. This outcome would be expected because when water is cooler, thyroid hormone levels will be lower, and the animal will continue growing as a juvenile.

Hot times, larger adult salamanders

On the other hand, the terrestrial adult salamanders were much larger during the warm period than during cooler periods. Again, this outcome would be expected because the heat on land would encourage faster metabolism, which would result in faster growth. The researchers found no difference in actual numbers between groups at cool vs. warm periods, but express concern that drying in Yellowstone today as a result of global warming might reduce the number of aquatic paedomorphs, affecting aquatic food webs.

From amphibians to gopher teeth

The same group also studied DNA from fossilized teeth of gophers and voles discovered in the cave. They found that during the dry period, gophers, who were stuck underground and isolated, experienced genetic bottlenecking, a reduction in diversity that persists today. However, the mobile, above-ground voles sought mates far and wide during the dry, warm period and actually experienced an increase in diversity. The lead researcher in the group compares early groups of isolated humans to the gophers, saying that they would have experienced a loss of diversity. But today’s population, with our ability to travel the globe with ease, is probably undergoing an increase in diversity since we’re able to mate with people a hemisphere away.

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Beautifully lifeless: the clearest ocean in the world

Thermohaline circulation

Because of the ability of UV light to shred biological molecules, researchers have speculated that life on Earth may have arisen in some dark corners, possibly under rocks or in the ocean depths where UV waves cannot reach. If that’s the case, we can rest assured that wherever life arose, it couldn’t have been a place containing the “clearest ocean waters on Earth.” That recognition today goes to a patch of water the size of the Mediterranean but lying in the middle of the Pacific, an ocean with a reputation for bounty. This area of the Pacific, however, although boasting waters of a unusual, deep violet color, is as lifeless as it is lovely.

Tough research job, but someone’s gotta do it

Researchers traveling to the area in October 2004 had been attracted to this part of the Pacific—stops included Tahiti, French Polynesia, Easter Island, and Chile—because of satellite images suggesting remarkably low chlorophyll levels in the area. This imaging allows scientists to track chlorophyll abundance in the Earth’s oceans, an important indicator of change on a major scale. When chlorophyll is low, life is scarce.

Indeed, when they traveled to the area, the researchers found some of the clearest ocean waters they had ever seen. According to one scientist on the project, the water was as clear as any of the clearest freshwater anywhere on the planet. He compared it, for example, to the clarity of the water from Lake Vanda, a pristine Antarctic lake lying buried under mountains of ice.

No chlorphyll, little life, but great clarity

But this clarity arises from a lack of chlorophyll and a lack of life. The researchers found that UV could penetrate to extraordinary depths in this area of the Pacific, as deep as 100 meters below the ocean surface. This depth sets a record for UV penetration in ocean waters, and its DNA-destroying properties carry responsibility for the dearth of life in this patch of the Pacific.

The mystery of the organic carbon

The researchers did find some evidence of a food web, however. But the organisms that live there, generally bacterial, must survive in a sort of closed system, constantly recycling the nutrients they need to live, such as nitrogen and phosphorus. Strangely, the team found that this particular part of the ocean was full of dissolved organic carbon, which is of biological origin. How an area so devoid of life could produce so much carbon derived from life remains a mystery. Researchers speculate that the bacteria are so busy addressing their nutrient needs in their limited system that they simply do not get around to degrading the carbon.

Out of the mix

Why would the Pacific harbor this clear, beautiful dead zone? The formation of this odd stretch of sea relies on several factors. The Earth’s oceans are a connected, global system of currents, water running not only at the surface but also at the depths. The thermohaline circulation, also known as the “global conveyor belt,” is one of these currents, driven by changes in the density of water in different parts of the globe. As water warms or becomes more saline, its density changes—warmer water is less dense than cold, and saltier water is more dense. As wind-driven currents move water toward the poles, the water cools and sinks when it gets to the high latitudes. This heavier water then flows back into the ocean basins and eventually wells up again. The oldest waters can take 1600 years to make this trip, but in the meantime, waters mix in the basins, making all of the Earth’s oceans pretty similar as they move their components around the planet.

The clearest ocean water on Earth, however, misses the trip. Its location in the middle of the South Pacific ensures that it doesn’t benefit from global river or ocean circulation. It never cools because it’s in the South Pacific, and thus, the water just stays put, clean and clear and almost completely lifeless.

The lovely bones: Terra preta to save our terra firma?

Charred bones set to save the world?

The Amazon river basin is home to the famous Amazonian “dark earth,” or terra preta, which recently made the news as more proof of large civilizations in the tangled Amazon forests.  This soil is renowned for its fertile properties, its loose consistency, water-holding abilities, and of course, its dark color. The people who used this earth generations ago—as many as 3000 years ago, according to one researcher—may have had no active interest in “greening” the planet, but they were very interested in getting a good crop yield for their efforts. Terra preta probably gave them just that.

Ancient farming wisdom

Somewhere along your educational path, you may have learned a few tips about farming. Rotate your crops. Let fields take a break. Till the soil. What you may not have understood as clearly were the natural processes that drove this farming wisdom.

When farmers turn over the soil, they loosen it. Earth happens to be the largest sink of carbon on terrestrial Earth, and when we move it around, some of that carbon gets released. When we try to fertilize it using dead and decomposing organic matter—compost, manure—this approach works in the short term to restore some nutrients, but microorgansims make pretty quick work of these organic remnants, returning carbon to the atmosphere again as carbon dioxide.

Thus, standard farming techniques of tilling and fertilizing and applying manure are short-lived efforts to keep the soil nutrient rich enough for planting. If nutrients are low, crop yield will be, too. And then there’s the water consideration; if the soil holds too little water or too much, that will also affect crop yield.

Magical fairy dust for crops

These factors all combine to make the terra preta soil look like magical fairy dust for crops. The soil actually is charcoal—or, in the lingo of the scientists who work with it, biochar. It is made from the rapid, pressurized burning of dead stuff—bones, tree bark—and manure. Pack it all into a metal container with a little hole for some pressure to escape, heat it to about 400 degrees Celsius, and you’ve made yourself some biochar. It apparently looks just like the charcoal you’d use at a cookout, but it has many more uses.

The carbon in the biochar is pretty inaccessible to microorganisms that would break it up, so it lasts a lot longer in the soil than your average, uncharred manure. In fact, it’s so long lasting that it’s still around in the Amazonian river basin long after the ancient farmers who used it disappeared. In addition to being a nutrient-rich and nutrient-tight source of carbon, biochar also is quite grabby with water, holding much more water than your average soil sample. That feature means that less water is required to grow crops in a biochar-laced field than would be needed in a regular, every-day kind of field.

Could soil invented in the Amazon save the Amazon?

Plants growing in the stuff do so faster, more robustly, and in greater numbers, primarily because of the rich nutrient source the biochar provides. Research indicates that the optimum combination is biochar plus fertilizer, which gives the greatest crop yield compared to either alone or neither. Using biochar could dramatically enhance global crop yields while decreasing water use and without adding a single acre of cropland. Using soil invented in the Amazon to save the Amazon rainforest has a nice “the circle is complete” aspect to it.

Although biochar has the drawback of having to be made and transported, its benefits to the planet don’t end with crop yield and water savings. The smoke generated from its preparation, in a process called pyrolysis, can be collected and used to form bio-oil, a form of renewable energy. In addition, biochar has potential as a sponge to soak up phosphates and nitrates from fertilizers before they reach our waterways, a sort of barrier against pollution. Last, this dark, magical fairy dust not only reduces carbon dioxide emissions from cropland but also significantly decreases methane and nitrous oxide emissions, both greenhouse gases that are far more potent than carbon dioxide but get considerably less press.

Termite toots causing global warming?

Termites to blame for global warming?

I was, um, in the bathroom at the Denver Zoo listening to the info feed the nice woman with the colonial accent was providing for folks using the facilities. The facts are all about poop and related activities, which I suppose is appropriate to the moment at hand. To add to the excretory atmosphere, the stall doors bear representations of animal hindquarters. Just letting you know that in case you ever want to stare at a close-up view of a baboon’s rear while you’re micturating. At any rate, as I was washing my hands, I heard a little tidbit about termites and greenhouse gases. The pleasant voice informed me that termites contribute a good percentage of the world’s greenhouse gases to the atmosphere, in the form of methane. Tooty little buggers, they must be.

It’s true. More methane than cows

Like most animals that survive on cellulose-based diets, termites have friendly micro-organisms that help them break down normally undigestible macromolecules. In the process, the micro-organisms produce a lot of methane gas. That gas, whether it’s in a cow or a termite, has to go somewhere, and that somewhere is out. Contrary to what some people may think, and according to the pleasant voice at the Denver Zoo, termites expel more of this stuff than cows do.

Should we blame the bacteria instead?

Actually, the helpful gut micro-organisms in termites are not all bacteria. Some are protozoans, depending on the termite species. But they’d be nothing without their hosts, so I guess we can just go ahead and blame them both. And I blame the Denver Zoo and their scatalogically oriented bathroom experience for the existence of this particular blog post.

Should we kill all the termites?

Well, that’s a terrible idea for any number of reasons, but as it turns out, it’s also not gonna help. One of the primary poisons used to knock of the wood-chewing insects happens also to be a “powerful greenhouse gas.” In addition, termites serve as a model for efficient harvesting of energy from biofuels, pulling about 90% from what they take in, compared to humanity’s sadly low success rates. So, yes, they eat our houses and expel about 15% of the methane in the atmosphere, but…they’re still better than we are at efficiently extracting energy from what they take in.

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