These animals are also plants

1 00:00:00,000 --> 00:00:09,800 Take a good look at this slug. 2 00:00:09,800 --> 00:00:12,520 No, not that, that's a leaf. 3 00:00:12,520 --> 00:00:13,520 This slug. 4 00:00:13,520 --> 00:00:15,520 There we go. 5 00:00:15,520 --> 00:00:21,360 Elysia chlorotica may not look like much, okay, it looks like a bright green leaf, but 6 00:00:21,360 --> 00:00:25,040 it's one of the most extraordinary creatures around. 7 00:00:25,040 --> 00:00:30,559 Living in salt marshes along the east coast of North America, it can go about a year without 8 00:00:30,559 --> 00:00:32,240 eating. 9 00:00:32,240 --> 00:00:36,880 During that time, it lives like a plant. 10 00:00:36,880 --> 00:00:41,759 Generally speaking, animals are what are called heterotrophs, meaning they can't produce their 11 00:00:41,759 --> 00:00:42,759 own food. 12 00:00:42,759 --> 00:00:45,240 They're consumers of other life. 13 00:00:45,240 --> 00:00:49,680 Plants, meanwhile, are autotrophs, or producers. 14 00:00:49,680 --> 00:00:56,439 They can synthesize their own fuel from sunlight, CO2, and other inorganic compounds. 15 00:00:56,439 --> 00:01:01,080 Plants do this by using organelles called chloroplasts, which give them their bright 16 00:01:01,080 --> 00:01:06,199 colors and convert sunlight into food through photosynthesis. 17 00:01:06,199 --> 00:01:09,480 Elysia is what's called a mixotroph. 18 00:01:09,480 --> 00:01:14,839 It can both consume food, like animals, and produce its own through photosynthesis, like 19 00:01:14,839 --> 00:01:15,839 plants. 20 00:01:16,160 --> 00:01:22,519 In fact, Elysia steals its ability to photosynthesize from the algae it eats by piercing the algal 21 00:01:22,519 --> 00:01:27,279 cells with specialized pointy teeth called radula. 22 00:01:27,279 --> 00:01:32,480 It sucks the cell empty and digests most of its contents, but the chloroplasts remain 23 00:01:32,480 --> 00:01:33,480 intact. 24 00:01:33,480 --> 00:01:39,519 They're incorporated into the epithelial cells lining Elysia's digestive system that branches 25 00:01:39,519 --> 00:01:41,680 throughout its flat body. 26 00:01:41,680 --> 00:01:48,199 This makes the slug look even more leaf-like, providing camouflage as well as food. 27 00:01:48,199 --> 00:01:53,839 As incredible as this adaptation is, there are more than 70 species of slug that steal 28 00:01:53,839 --> 00:01:56,480 chloroplasts from their food. 29 00:01:56,480 --> 00:02:02,360 What makes Elysia and a few closely related species in the Mediterranean and Pacific unique 30 00:02:02,360 --> 00:02:05,559 is how long they can hold onto chloroplasts. 31 00:02:05,559 --> 00:02:09,000 Most other slugs keep them for a few weeks at most. 32 00:02:09,000 --> 00:02:15,240 This longevity seems to be due to the survival abilities of both plastids and slugs. 33 00:02:15,240 --> 00:02:20,639 Specifically, the chloroplasts of certain algae can repair their own light-harvesting 34 00:02:20,639 --> 00:02:26,279 systems, while most chloroplasts are thought to rely on their host cell and its genes for 35 00:02:26,279 --> 00:02:27,679 repairs. 36 00:02:27,679 --> 00:02:33,119 This makes the chloroplasts able to sustain themselves for longer inside this slug. 37 00:02:33,119 --> 00:02:38,919 Meanwhile, the slug adjusts its gene expression to improve its relationship with the chloroplasts 38 00:02:39,320 --> 00:02:45,160 and removes damaged plastids to avoid accumulation of potentially damaging chemicals. 39 00:02:45,160 --> 00:02:50,639 Though few species can steal organelles from another species' cell, these slugs are far 40 00:02:50,639 --> 00:02:54,520 from alone in getting an assist from plants. 41 00:02:54,520 --> 00:03:01,119 Organisms as diverse as corals, giant clams, and sponges have symbiotic algae living inside 42 00:03:01,119 --> 00:03:07,039 their cells, supplying them with organic compounds through photosynthesis. 43 00:03:07,039 --> 00:03:12,559 In turn, they supply their little helpers with shelter and inorganic compounds. 44 00:03:12,559 --> 00:03:17,000 Some of these myxotrophs even transmit the algae to their offspring. 45 00:03:17,000 --> 00:03:22,199 Without the aid of these algae, filter-feeding corals, clams, and sponges would not gain 46 00:03:22,199 --> 00:03:28,320 enough nutrition in the nutrient-poor tropical ocean, and the dazzling coral reefs they build 47 00:03:28,320 --> 00:03:31,440 simply would not exist. 48 00:03:31,440 --> 00:03:33,639 Myxotrophy even cuts both ways. 49 00:03:33,639 --> 00:03:40,000 An alga called Tryposphorica can consume several microscopic animals a day, allowing 50 00:03:40,000 --> 00:03:43,240 it to survive in darkness for weeks. 51 00:03:43,240 --> 00:03:48,639 Trypos is in turn eaten by other myxotrophic algae, providing frequent opportunity for 52 00:03:48,639 --> 00:03:52,360 exchange of organelles such as chloroplasts. 53 00:03:52,360 --> 00:03:57,720 This seems to allow some algae to survive in parts of the dark ocean such as the Mariana 54 00:03:57,720 --> 00:04:02,240 Trench, which plants otherwise wouldn't be able to inhabit. 55 00:04:02,240 --> 00:04:08,479 The processes by which Elysia becomes photosynthetic and Trypos switches between feeding modes 56 00:04:08,479 --> 00:04:13,759 are reminiscent of what scientists believe led to the origin of all plants. 57 00:04:13,759 --> 00:04:17,720 Single-celled animals preyed on cyanobacteria. 58 00:04:17,720 --> 00:04:23,200 Some of these tiny plants were not digested and lived on in the animal cells, eventually 59 00:04:23,200 --> 00:04:26,600 giving rise to chloroplasts. 60 00:04:26,600 --> 00:04:31,880 But these first eukaryotic plants were soon consumed by other animals, which hijacked 61 00:04:31,880 --> 00:04:35,959 the precious chloroplast just like Elysia. 62 00:04:35,959 --> 00:04:41,119 And following the example of eating and being eaten, we've seen in the case of Trypos, 63 00:04:41,119 --> 00:04:47,320 this chloroplast heist happened up to three times, giving rise to plastids with more membranes 64 00:04:47,320 --> 00:04:53,040 and the ocean's most productive plants and forests. 65 00:04:53,040 --> 00:04:59,640 This slug-slash-plant is just one of millions of species that uses crafty evolutionary adaptations 66 00:04:59,640 --> 00:05:01,239 to survive. 67 00:05:01,239 --> 00:05:02,720 Take the orchid. 68 00:05:02,720 --> 00:05:05,679 Just a pretty flowering plant, right? 69 00:05:05,679 --> 00:05:06,679 Wrong. 70 00:05:06,679 --> 00:05:10,880 Find out about their sneaky tactics of deception with this video.