How Plants Became Carnivores

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I love that channel

👍︎︎ 2 👤︎︎ u/naamalbezet 📅︎︎ Oct 08 2020 🗫︎ replies

I've been wondering about their evolution. Thanks!

👍︎︎ 1 👤︎︎ u/buggybugnow 📅︎︎ Oct 08 2020 🗫︎ replies
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Sometime in the Eocene Epoch, more than 35 million  years ago, in a warm coastal forest near the   Baltic Sea, the resin of a conifer tree dripped  onto the narrow, pointed leaves of a plant below. Over time, that resin hardened into  amber, trapping bits of the plant inside. These tiny leaf fragments, just  half a centimeter in length,   belong to the same plant family  as the modern genus Roridula Today, those plants are found only in a section  of southwestern South Africa called the Cape   Floristic Region, but their family was clearly  much more widespread during the Eocene Epoch. And... they’re carnivorous -  these plants actually trap prey.  That makes these tiny bits of leaves encased in   amber the best fossil evidence  we have of carnivorous plants. But! That doesn’t mean they were  the first carnivorous plants. Because carnivory has actually  evolved independently at least   nine times in plants -- and in plants that  aren’t all that closely related to each other. So it looks like something keeps driving  plants to this seemingly extreme lifestyle. But what?  How and why does botanical  carnivory keep evolving? Well, it turns out that when any of the basic  things that most plants need - sunlight, water,   and nutrients - aren’t there, some plants can  adapt in unexpected ways to make sure they thrive. If you find carnivorous plants strange  and fascinating, you’re not alone.  Charles Darwin published an entire book about them  in 1875, after spending a decade or so trying to   figure out exactly how they worked.     But it would take another hundred-plus years  before scientists would propose the definition   of what counts as a carnivorous  plant that’s often used today. There are essentially two things that a  plant has to do to be considered carnivorous. First, it has to have the ability  to take in nutrients from dead prey   on its surfaces or trapped inside it.  That prey is usually insects, though  sometimes it includes small vertebrates,   like the northern pitcher plants that  have been observed consuming salamanders. And by definition, doing this has to give the  plant an advantage in growing or reproducing. It’s not enough for the plant to just  have defenses that can kill an animal   that’s trying to snack on it. It also  has to get those animals’ nutrients. Second, the plant needs to have at least  one adaptation that actively lures in,   catches, or digests its prey.  Doing at least one of these things   and absorbing the nutrients for your  benefit makes you a carnivorous plant.  But! Because this is nature, there  are always exceptions to these rules.  Like, the living relatives of that  fossil plant preserved in amber   do trap arthropods, but their sticky  secretions can’t digest them.  Instead, the trapped prey attracts  insects in the genus Pameridea,   which don’t get stuck to the plant.  The insects then eat the trapped  arthropods and poop on the plant,   which in turn absorbs the  nitrogen from their poop!  So, these plants get a mutualist to do the work of  digestion for them - but they still benefit  from   the death of their prey, so some botanists  count them among the carnivorous species. And there are actually a lot of plants alive today  that meet the criteria for carnivory - from about   580 to more than 800 species, depending on  what definition of carnivory you’re using. Carnivorous plants are found on every continent  except Antarctica. And they appear to have evolved   between 95 million and 1.9 million years  ago, based on molecular clock methods.  Now, this might seem like a  really wide range of dates,   but remember, there wasn’t just  one origin of carnivorous plants. For example, a key genetic change in the  evolution of carnivory took place in a common   ancestor of Venus flytraps and sundews  that lived about 60 million years ago. Meanwhile, the pitcher plants of North and South   America seem to have originated  around 48 million years ago.  And the youngest botanical carnivores  appear to be two species of bromeliad   native to parts of northern South America  that evolved around 1.9 million years ago. That means botanical carnivory is  an example of convergent evolution,   when organisms that aren’t closely related  develop similar adaptations independently,   in response to similar environmental pressures. Now, over millions of years  and across hundreds of species,   plants have developed five different types  of traps, most of them many separate times.  And traps can be passive, if prey just  falls into them and can’t escape, or active,   if the plant actually moves to catch its prey. Pitfall traps are the standard passive trap used  by things like pitcher plants and bromeliads.   Prey lands on the plant’s slippery surface and  slides down into a pool of digestive juice.   
Then there are flypaper traps, which are just  what they sound like - prey becomes stuck in   a sticky substance that is produced by the  plant’s leaves. These traps can be passive   or active - for example, sundews have moving  sticky tentacles that react to contact with prey. There are also snap traps which are active,   using rapid modified leaf movements, like  those of a Venus flytrap, to snag prey. And Bladder-suction traps are found  exclusively in plants called bladderworts.   They create little negative pressure  vacuums inside their traps, which,   when triggered by prey, pop open and suck  the victim inside before snapping closed. Finally, there are eel-traps  or lobster-pot traps -- passive   traps that force prey to move toward the  plant’s digestive organ by having little   inward-pointing hairs that keep prey  from moving backward out of the trap.  And what’s even cooler is that  all of these unrelated plants   have not only developed the same kinds of traps,   but it looks like they’ve also evolved the same  molecular mechanisms for digesting their prey.

  For example, the lineages of three  different kinds of pitcher plants   split more than 100 million years ago, probably  well before any of them became carnivorous.  And they each produced their own proteins that  were originally used to defend the plants from   attackers, like fungi. But over time, all of those  proteins became repurposed into digestive enzymes. Basically, their function  remained essentially the same,   but changes came about as to where  and how they were being used. Fungi support their cell walls  with a starchy polymer called   chitin. And chitin is also the  basis for arthropod exoskeletons.  So, proteins that were first used to fight fungal  parasites eventually became chitinase - the enzyme   in the digestive fluid of the pitcher plants  that breaks down those crunchy exoskeletons. All three of these lineages have also  evolved to use purple acid phosphatase,   another enzyme, to absorb  phosphate from their victims. Okay, so how botanical carnivory keeps  popping up seems pretty well understood. But there’s still the question of why? Well, it goes back to the  idea of convergent evolution.   All these different carnivorous plants are  responding to similar environmental pressures. Across the globe, they’re generally  found in open, sunny places that   have moist -- but nutrient-poor -- acidic  soils. Many of them live in bogs or fens. But a plant has to get nitrogen  and phosphorus somehow.  And in these kinds of habitats,  botanical carnivory represents   an evolutionary trade-off - one that  comes with both costs and benefits. See, a carnivorous plant has two types of  leaves: regular ones that photosynthesize   and ones that have been modified  into their particular kind of trap.  This means they have fewer photosynthesizing  leaves than a regular, non-carnivorous plant. So they have to live in places with  lots of sunlight, to try to maximize   their ability to photosynthesize - and  they have to make up the difference. Carnivory can only evolve in situations where  it benefits the plant more than investing in   regular leaves, like in places where the  soil is lacking nitrogen and phosphorus.  And carnivorous plants will even stop  being carnivorous, at least temporarily,   if they’re placed in nutrient-rich soil or  if they don’t get enough water or light. As for what plant was the first to evolve this  strange adaptation, well, we don’t really know. Carnivorous plants are pretty rare and they’re  only found in certain kinds of habitats,   so they’re just less likely to fossilize than  other kinds of plants that are more widespread. And the oldest reported fossils of carnivorous  plants - one from the Early Cretaceous Period   of China and another from the Late Cretaceous  of the Czech Republic - are controversial.  Beyond that, the only other halfway-decent  evidence we have of ancient carnivorous   plants are pollen grains from the Paleocene  Epoch of India and one fossil seed from the   Eocene Epoch of Australia that was destroyed in  a freak lab accident after being photographed.    But, because neither of these are fossils   of the actual leaves themselves, we can’t be 100%  certain whether the plants they came from actually   were carnivorous, or whether they’re just related  to modern plants that are carnivorous today. So, the jury is still out on these early  carnivorous plants - leaving us with just the   leaf fragments of that Roridula relative preserved  in amber as the oldest undisputed evidence. It’s kind of ironic, if you think about  it -  a plant that used sticky goo to trap   its prey got stuck forever in the  sticky secretion of another plant. Ultimately, the how and why of  carnivorous plants teaches us   one of the fundamental facts of evolution...  That distantly related organisms can wind   up finding similar solutions to  the same problem: how to survive. Hey everyone! Feeling a little stuck inside? Then  you should check out Overview, a brand new show   on PBS Digital Studios’ science and nature channel  Terra. Overview combines mesmerizing drone footage   with in-depth science storytelling to reveal all  the things shaping our planet from the 10,000 foot   view (literally). So go over to Terra, subscribe  and make sure to tell them Eons sent you! We’d also like to say thanks to our friends over  at Deep Look who provided us with some spectacular   up-close footage of sundews.  Be sure to check  out their episode, “Cape Sundews Trap Bugs in   A Sticky Situation” to learn more about these  carnivorous plants - link is in the description.  Big thanks to this month’s Eontologists  for sticking with us: Lucan Curtis-Mahoney,   Sean Dennis, Jake Hart, Jon Davison Ng, Patrick  Seifert, and Steve! Become an Eonite by supporting   us at patreon.com/eons. And remember - Eonites  get perks like submitting a joke for us to read! Like this one from James H What did the paleontologist name his son? Cam Brian! Get it? Cam..cam...Cambrian? It's good. Thanks James! And as always thank you for joining  me in the Konstantin Haase studio. If   you like what we do here, go to  youtube.com/eons and subscribe!
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Channel: PBS Eons
Views: 1,525,285
Rating: 4.9501238 out of 5
Keywords: dinosaurs, dinos, paleo, paleontology, scishow, eons, pbs, pbs digital studios, hank green, john green, complexly, fossils, natural history, carnivorous plants, convergent evolution, roridula, amber, baltic amber, pitcher plants, venus flytrap, bladderwort, sundew, passive traps, active traps, pitfall trap, sticky trap, flypaper trap, snap trap, lobster-pot trap, eel-trap, bladder-suction trap, chitinase, purple acid phosphatase, plant evolution, botanical carnivory, paleobotany, evolution
Id: aGJ7tg0ifmo
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Length: 11min 12sec (672 seconds)
Published: Wed Oct 07 2020
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