• Secrets in Amber: How Trees Help Preserve Essential Prehistory

    Daniel Lewis on the Millennia-Long History of Insects, and What It Can Teach Us

    “Great things are done… by a series of small things brought together.”
    –Vincent van Gogh
    *

    Animals don’t get much stranger than the tardigrade. It’s a boneless little creature, a chubby, eight-legged, microscopic organism that lives mostly in water, although it can live anywhere, and I mean anywhere. It’s not what you’d think an unstoppable organism would look like. If it were bigger you might consider it cuddly. Despite its sharp claws, and a megaphone-shaped snout where you’d expect its face to be, it’s a cute, clumsy crawler, staggering along like a newborn puppy.

    The tardigrade can live in hot springs, deep under the sea, and beneath solid ice at both poles. In tests, it’s survived being boiled, frozen, dried out, and even subjected repeatedly to the intense radiation of outer space. Its evolutionary past, and the futures it contains, are embedded in the amber from a tree that’s so old it has no common name, known only as Hymenaea protera. It’s not an exaggeration to say that the tardigrade holds secrets that could offer salvation from the effects of climate change.

    In 1773, J.A.E. Groeze, a German pastor with a zest for microscopy, first identified the tardigrade, which he named using the French adjective for “slow-moving.” News of the animal’s freakish survival abilities spread quickly; in 1800, Edinburgh Magazine called tardigrades “the colossuses of the microscopic world.” Because tardigrades are micro-sacs of goo (albeit with mouths, rectums, and esophagi), they don’t fossilize.

    But three of their intact remains from deep time have been found—all in amber, spread out over nearly sixty years of painstaking searching between 1964 and 2022. Scientists would like to understand how tardigrades came to be such extremophiles, able not just to survive radiation in outer space, but to suspend their metabolism when going dormant. Studying the biology of tardigrades over long timeframes could provide new understandings of what selective pressures, what mutations, and what circumstances gave them such profoundly effective survival skills. The search for more tardigrades in amber continues.

    It’s not an exaggeration to say that the tardigrade holds secrets that could offer salvation from the effects of climate change.

    Ideas about how the tardigrade could help humans are more than speculative. Japanese scientists have already studied tardigrade proteins to see if they can come up with a more effective sunscreen, binding tardigrade proteins to human cells in the laboratory to develop a more radiation-resistant product. This work produced cells that showed a 40-50 percent reduction in x-ray damage to skin: useful if prone to sunburns, but essential if you’re at risk from, say, radiation poisoning. Scientists have identified about a thousand different species, living just about everywhere. There is no organism hardier than the tardigrade, and none potentially of greater use.

     *

    H. protera grew across large portions of what was once the combined continent of Africa and South America. The tree lived about 25 million years ago, probably growing tall and leafy, branching out with a large crown, reaching above 120 feet and occasionally emerging above the surrounding canopy. It had tan-colored petals, and provided leaves and fruits to a menagerie ranging from tiny insects to large mammals. Bats, bees, butterflies, moths, and other insects pollinated its flowers.

    As with almost all fossil trees, it has no common name. But H. protera had a messenger in its biology: the amber that began as a sticky resin, exuded by trees from wounds, and then hardened into rocklike form. Amber has conserved abundant and diverse biological evidence of ancient species from millions of years ago: a map of the planet’s ancestors that offers a route to better understanding evolution and current life on earth. We now know well that the natural world is reliant on parts working on approximate harmonies with each other. But our understandings of the linkages between past and present life are nowhere near as clear, in part because the record from deep time is so incomplete.

    *

    Because amber traps organisms in a blob of oxygen-free resin, the stilled life within is preserved with its components intact: chloroplasts, cell nuclei, pigments. The fidelity of insect details in particular astonishes. We can see a termite pollinating a flower; we can see flies having three-dimensional sex; we can view the flight muscles of a stingless bee; we can even observe the folded membranes of mitochondria.

    Studying fossils in amber after studying fossils in rock has been likened to switching from grainy black-and-white television to high-definition color film. Put another way, fossils whisper about the climate past, but amber speaks in a rich, clear voice. It’s a small-scale operation. Bigger insects can often wrestle free; the longest insects ever discovered in amber are about two and a half inches long.

    Because amber immediately enrobes its foreign contents in oxygen-free ooze, it preserves anatomy, soft parts, and feathers in three dimensions. As a bonus, most amber also contains compounds that inhibit bacterial growth, further keeping the specimen from decaying. Fossils, by contrast, tend to be squashed, given that they’re formed between layers of sediment.

    *

    Insects witnessed the rise and fall of the dinosaurs, and the cascading effects of humans coming into the world, and everything in between. The greatest percentage of life trapped in amber consists of arthropods: insects and spiders. (Most high-school biology students will remind you that they’re not the same; insects have three body parts and six legs; spiders have just two body parts, eight legs, and usually, eight eyes.) There are about 45,000 known species of spiders.

    But they’re completely outpaced by insects; entomologists have described more than a million species of insects worldwide, and these represent more than half of all known living organisms. There may be as many as ten million insect species, and in their totality these might constitute over 90 percent of animal life on Earth. Understanding this corpus of bugs lets paleoentomologists align the present with the past, fitting newly described species of amberized insects into locations on the tree of life that constitutes the enormous, complex puzzle of diversification.

    Researching insects from a long time ago can also provide news about pest evolution, pollination, and even gigantism—the tendency for some prehistoric insects to grow to a very large size—as a result of climate change. Comparing prehistoric insects with modern relatives frequently uncovers secrets, or provokes important questions: What classes of insects were smaller then, and why; what has caused them to be larger, and what does that mean for our future relationships with insects? These are a scant handful of the investigations entomologists make, with the essential help of this tree sap. The effects of long-term environmental conditions and change are inscribed on evolved bodies.

    Insects in amber are especially useful for the inferences they help scientists draw about plants. Botanic matter appears in resin, including grasses, small flowers, seeds, and little leaves. It’s clear from the presence of once-living organisms in these amber nuggets that the natural world was a wildly diverse, disruptive, and crowded place millions of years ago.

    We know that many classes of insects depend on specific types of flowers, fruits, or leaves that don’t themselves occur in the amber, either because those plant parts are too large, or don’t grow in ecosystems sufficiently near to the trees. Figs are known to have been present in some places entirely because of the presence of certain kinds of wasps in amber.

    The wasps and the figs have formed a symbiotic relationship over the eons: the wasps pollinate the flowers, which in turn give the wasps a safe place for raising their wasp young. Another example is the presence of the palm bug (Paleodoris lattini) in amber. The bug implies the nearby presence of the palm; its flattened body lets it live between the palm’s tightly-closed frond leaves.

    The wealth of arthropods in amber is an entomophobiac’s nightmare: at least fifty different species of spiders, as well as scorpions, mites, ticks, winged ants, midges, termites, earwigs, bees, leafhoppers, leafcutters, and butterflies. Finds of insects in amber have provided a window into defensive and offensive mechanisms, social and mating behaviors, and bug sex, caught in flagrante (from the Latin for “in blazing fashion”) for millennia.

    Acts of desperation abound: a leaf beetle blowing noxious bubbles in a last, frantic attempt to defend itself against the resin in which it’s just been trapped; worker ants trying to carry their brood to safety—nature frozen in tooth and claw. Many flies reflexively lay eggs when they die, and there are many female flies in amber that have eggs trailing behind: a final effort to create life out of death.

    Liquids are especially important finds in amber because they’re not found in fossils. The magic of permineralization in traditional fossils can only go so far, and it won’t preserve any bodily fluids, or any kind of soft, gelatinous material, or saliva—only stone traces of those liquids.

    Only in recent decades have we been able to identify even modern species from their blood. DNA can survive for up to about 1.5 million years, but not much longer. So efforts to harvest the much older DNA from amber specimens are only speculative. But if enough usable DNA were extractable from amber, it could pinpoint the animal from which the tick or other biting insect had taken its last meal.

    Finding more tardigrades would help us understand their evolutionary histories, to help us further our futures.

    The world’s amber has moved around the planet in an endless churn. Most amber floats, which means that water has swept much of it around the world, sending it down rivers where it eventually becomes stranded and concentrated along the banks or swept out to sea. But like innocent witches, a lot of fresh amber also sinks, depending on its density, which can vary greatly.

    Sometimes amber hunters extract it from shallow ocean waters, often by sucking up quantities of rocks from the bottom of shorelines: a miner’s approach to finding a kind of tree gold. The lessons it can provide seem limitless. Only recently has true structural color from ancient creatures been discovered in amber, and color can provide a bucketful of clues about an insect’s behavior and ecology because of its role in camouflage, thermoregulation, and diverse communications strategies, including attracting mates. Some ancient insects caught in amber are purple, blue, and vibrant metallic green.

    *

    So what lets the tardigrade survive extreme conditions? Scientists finally sorted it out several years ago, and it’s a very neat multi-part trick. When it senses that dry conditions are approaching, it pulls its head and limbs into its exoskeleton, stops moving, and waits for water. Tardigrades can stay in this dormant state for decades, popping back into motion when water returns.

    But desiccation isn’t its only tool; other less hardy animals have the ability to live in a dried-out state for long periods of time, such as brine shrimp and nematode worms. Those animals use a sugar known as trehalose to protect its cells from the damage that dehydration brings. Microbiologists speculated for a long time that trehalose was how the tardigrade protected itself.

    However, the process is completely different. As it dries out, the water bear, in a stunning feat of transformation, turns most of itself temporarily into glass, producing something called intrinsically disordered proteins. This glass coats the cell’s molecules, protecting them. A tiny bit of water still remains in the most dried-out tardigrade, and in concert with these proteins—the exact mechanisms remain unknown—the tardigrade vitrifies, and suspends itself from the rest of the world, waiting to be reborn: Sleeping Beauty awaiting a hydrating kiss.

    Still other defense mechanisms are at work. A newly discovered species of tardigrade, Hypsibius exemplaris, offers another key to its survival skills. Hiding beneath its skin are fluorescent pigments that turn ultraviolet radiation into harmless blue light. Further, tardigrades have exceptionally robust DNA repair mechanisms, which spin into action.

    We don’t know if tardigrades found in amber have the same survival skills, or if they had completely different ones. Thanks to the ancient tree and its prolific amber production, we have abundant source material for amber. Finding more tardigrades would help us understand their evolutionary histories, to help us further our futures.

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    From Twelve Trees: The Deep Roots of Our Future by Daniel Lewis. Copyright © 2024. Available from Avid Reader Press, an imprint of Simon & Schuster.

    Daniel Lewis
    Daniel Lewis
    Daniel Lewis is the Dibner Senior Curator for the History of Science and Technology at the Huntington Library, Art Museum, and Botanical Gardens in Southern California, and a writer, college professor, and environmental historian. He writes about the biological sciences and their intersections with extinction, policy, culture, history, politics, law, and literature. Lewis holds the PhD in history and has held post-doctoral fellowships at Oxford, the Smithsonian, the Rachel Carson Center in Munich, and elsewhere. Lewis also serves on the faculty at Caltech, where he teaches environmental humanities courses, as well as at the Art Center College of Design in Pasadena. He is also currently serving a five-year term on the IUCN’s Species Survival Commission, as a Bird Red List Authority member. His previous books include Belonging on an Island: Birds, Extinction, and Evolution in Hawai’i and The Feathery Tribe: Robert Ridgway and the Modern Study of Birds.





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