WEBVTT 1 00:00:12.210 --> 00:00:17.212 The annelid species we are working with, Platynereis dumerilii, is a marine worm 2 00:00:17.512 --> 00:00:22.903 found worldwide in temperate seas. For the past several decades, researchers have 3 00:00:23.203 --> 00:00:27.568 no longer taken animals directly from the sea, but are able to raise them in the lab. 4 00:00:28.567 --> 00:00:33.417 Platynereis' full life cycle is completed easily and successfully in laboratory 5 00:00:33.717 --> 00:00:38.432 settings like here at the Institut Jacques Monod in Paris. We do not need to be 6 00:00:38.732 --> 00:00:41.112 close to the sea to study a marine animal! 7 00:00:53.228 --> 00:00:58.515 At the Institut, we breed the worm in a thermostatic room at 18 degrees. 8 00:00:58.813 --> 00:01:03.748 We raise them all year long in tupperware -like boxes with less than a litre of fresh 9 00:01:03.948 --> 00:01:07.897 seawater in it, which we change every two weeks, thanks to the help of the 10 00:01:08.197 --> 00:01:09.730 animal facility members. 11 00:01:19.500 --> 00:01:24.966 In the wild, Platynereis immature worms live within a silk tube they secrete on algae. 12 00:01:25.166 --> 00:01:31.214 In the lab in their boxes they also secrete a tube and live inside it most of the time. 13 00:01:31.585 --> 00:01:36.097 They are quite inactive and crawl out of the tubes only to grab some food. 14 00:01:36.297 --> 00:01:40.676 They are fed three times per week with ground fish food and organic mashed spinach. 15 00:01:41.990 --> 00:01:45.845 Platynereis worms are very sensitive to detergents, and for this reason are also 16 00:01:46.045 --> 00:01:49.700 used for ecotoxicology studies. 17 00:01:51.550 --> 00:01:56.505 Like many other marine animals such as corals, sea urchins, and even fishes, 18 00:01:56.705 --> 00:02:01.061 Platynereis' life cycle is synchronized with the lunar cycle, which we call a 19 00:02:01.360 --> 00:02:06.515 circalunar life cycle. Each worm will reproduce only once in its life, and the 20 00:02:06.715 --> 00:02:11.370 timing of this reproduction is tightly regulated by this lunar life cycle. 21 00:02:13.430 --> 00:02:17.419 In the culture room, we keep the worms, most of the time in a daily artificial 22 00:02:17.719 --> 00:02:23.948 illumination regime. We try to reproduce natural "summer" conditions and so we have 23 00:02:24.248 --> 00:02:29.519 a cycle of 16 hours of light and eight hours of darkness. On top of that, 24 00:02:29.788 --> 00:02:34.648 to induce sexual maturation, we need to mimic the lunar stimulus to initiate 25 00:02:34.848 --> 00:02:39.939 the reproduction phase. We thus artificially reproduce moonlight using 26 00:02:40.218 --> 00:02:46.112 a low-light lamp that we switch on at night for seven days on a 28-day cycle. 27 00:02:46.520 --> 00:02:50.549 A couple of days after this week of full moon, worms start to mature. 28 00:02:50.780 --> 00:02:55.454 We are extremely careful to respect this illumination and moonlight regime, as 29 00:02:55.754 --> 00:03:00.100 errors have been shown to have long- term negative effects on the culture, 30 00:03:00.310 --> 00:03:03.487 so the worm room schedule has to be followed meticulously. 31 00:03:06.127 --> 00:03:10.819 Maturation of worms occurs over two weeks. During this period, the members of the team 32 00:03:11.019 --> 00:03:15.281 are in charge of collecting animals that are in the course of maturation by checking 33 00:03:15.581 --> 00:03:20.288 all the worm boxes three times a week. We can easily recognise which adults 34 00:03:20.588 --> 00:03:24.709 are mature as they dramatically change their morphology, notably their colors. 35 00:03:25.409 --> 00:03:30.768 Males turn white (full of sperm in their anterior part) and red in their posterior 36 00:03:31.068 --> 00:03:34.597 part, while females become yellow (full of eggs). 37 00:03:34.897 --> 00:03:38.772 We can also find worms that are more or less orange, and at that time we are not 38 00:03:39.172 --> 00:03:44.112 sure if they will become male or female. Morphologically, it's quite unclear, but 39 00:03:44.412 --> 00:03:46.451 it's of course genetically determined. 40 00:03:46.651 --> 00:03:51.448 When we find mature or maturing worms, we collect them from their boxes using 41 00:03:51.732 --> 00:03:56.934 a pipette and place them in specific, separate boxes that either contain 42 00:03:57.234 --> 00:04:02.334 females or males. This way, we can choose the exact moment we will allow them to 43 00:04:02.634 --> 00:04:05.751 reproduce by putting a male and a female together. 44 00:04:08.700 --> 00:04:12.211 When males and females are ready to reproduce, they start to become quite 45 00:04:12.511 --> 00:04:16.967 active and they leave their tubes. When we want to induce a fertilization, we put 46 00:04:17.267 --> 00:04:21.585 a male and a female in a beaker together where they will start to swim elegantly 47 00:04:21.785 --> 00:04:27.196 around each other. They will soon release gametes almost simultaneously in the sea 48 00:04:27.496 --> 00:04:33.095 water, so the fertilization is external. Several thousand eggs are released by 49 00:04:33.395 --> 00:04:37.092 a big female, by spontaneous rupture of its body wall. 50 00:04:37.392 --> 00:04:41.531 Consequently, the female will have emptied itself in a couple of minutes and 51 00:04:41.831 --> 00:04:46.441 will soon die. The male can release its sperm thanks to a modified terminal part of 52 00:04:46.741 --> 00:04:52.728 its body and is able to release sperm a couple of times, but it too will die in a 53 00:04:52.952 --> 00:04:57.503 few hours. When the fertilization is done, we then put the beaker in a thermostatic 54 00:04:57.803 --> 00:04:59.847 room at 18°C to develop. 55 00:05:01.430 --> 00:05:06.018 Around 15 minutes after fertilization, a substantial egg jelly will be produced and 56 00:05:06.218 --> 00:05:11.498 will cover the whole developing egg. This jelly blocks the fusion of supernumerary 57 00:05:11.798 --> 00:05:16.718 sperm with the egg and protects the egg. It is also a clear indicator of successful 58 00:05:17.018 --> 00:05:22.618 fertilization. Indeed, when the fertilization has worked properly, the jelly is produced 59 00:05:22.918 --> 00:05:28.567 and the eggs are no longer in close contact. The jelly creates a regular spacing between 60 00:05:28.867 --> 00:05:32.477 the eggs and gives the whole a geometric shape. 61 00:05:32.910 --> 00:05:37.779 In contrast, if fertilization fails, the eggs will be stuck together at the bottom 62 00:05:38.079 --> 00:05:39.523 of the beaker. 63 00:05:42.340 --> 00:05:46.200 In the wild, it will be progressively removed by natural elements 64 00:05:46.453 --> 00:05:50.344 such as the movement of the sea, but in the lab, in order to allow a proper 65 00:05:50.644 --> 00:05:55.703 embryonic development, we have to remove it manually at around 24 hours post- 66 00:05:55.903 --> 00:06:01.340 fertilization. To do that, we use a net that retains the embryos and we rinse 67 00:06:01.540 --> 00:06:05.722 them with a lot of sea water to remove the jelly. Free of their jelly, 68 00:06:05.922 --> 00:06:08.914 they can now swim and can continue their development. 69 00:06:16.160 --> 00:06:20.514 Platynereis larvae will not need to eat for a couple of days as they will live on their 70 00:06:20.814 --> 00:06:25.651 reserves, but after around five days, the small larvae will become benthic and will 71 00:06:25.951 --> 00:06:30.771 thus start to feed on the bottom. At this stage, they are too small to eat fish food. 72 00:06:31.031 --> 00:06:35.541 So, in the lab, we specifically developed a culture of algae named Tetraselmis 73 00:06:35.841 --> 00:06:39.138 marinus to feed the young worms from five days to two months. 74 00:06:40.527 --> 00:06:45.076 In between, at around 10 days, we remove the larvae from the beaker with a pencil and 75 00:06:45.376 --> 00:06:49.800 place them in boxes filled with seawater and algae. At this stage, they are ready 76 00:06:50.100 --> 00:06:52.830 to join the rest of the collection in the worm room. 77 00:08:06.860 --> 00:08:11.152 Young worms, from 10 days to two months old, will be placed in a specific 78 00:08:11.452 --> 00:08:16.202 area of the worm room -a kind of kindergarten- and at that age, their 79 00:08:16.502 --> 00:08:20.470 seawater is not changed. They are too small for that and we may lose them 80 00:08:20.770 --> 00:08:25.035 during this procedure. After two months, they are big and strong enough to allow 81 00:08:25.279 --> 00:08:29.850 the seawater replacement and to feed them with fish food. They have grown a lot 82 00:08:30.150 --> 00:08:33.390 and they're thus very cramped in their small boxes. 83 00:08:33.890 --> 00:08:38.020 As we want them to continue to grow to become big mature worms, also named 84 00:08:38.320 --> 00:08:43.700 atoke worms, we will need to separate them. This "transplanting" procedure allows us 85 00:08:44.000 --> 00:08:48.751 in a matter of a couple of weeks to obtain much bigger of juveniles, also named 86 00:08:49.051 --> 00:08:54.431 epitoke worms. Epitoke worms will continuously grow throughout their lives 87 00:08:54.631 --> 00:08:58.270 until they reach maturity and the life cycle is fully completed.