1 00:00:01,840 --> 00:00:07,720 Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey, brain Stuff, 2 00:00:07,800 --> 00:00:12,639 Speaker 1: Lauren vogelbaumb here. Reproduction and birth are pretty much always 3 00:00:12,640 --> 00:00:17,599 Speaker 1: weird miraculous, sure, but none of us animals, human or otherwise, 4 00:00:17,800 --> 00:00:21,360 Speaker 1: get carried in on storks. But if you've ever tried 5 00:00:21,400 --> 00:00:24,520 Speaker 1: to explain the process to a small child, just be 6 00:00:24,720 --> 00:00:29,440 Speaker 1: glad that we're not sharks. A shark can be born 7 00:00:29,680 --> 00:00:33,160 Speaker 1: three different ways, including live birth, hatching from an egg, 8 00:00:33,400 --> 00:00:37,440 Speaker 1: and an egg slash live birth combination. Plus in some 9 00:00:37,520 --> 00:00:41,080 Speaker 1: shark species, you have to survive gestation without being eaten 10 00:00:41,240 --> 00:00:45,839 Speaker 1: by your developing siblings. We'll get to that in a minute, 11 00:00:45,880 --> 00:00:49,120 Speaker 1: but first let's look at how sharks get pregnant. As 12 00:00:49,159 --> 00:00:52,680 Speaker 1: opposed to other fish. Sharks use internal fertilization in a 13 00:00:52,720 --> 00:00:56,440 Speaker 1: process that can appear violent to humans. The male shark 14 00:00:56,560 --> 00:00:59,400 Speaker 1: often bites the female's fins or back to keep her 15 00:00:59,440 --> 00:01:03,080 Speaker 1: in place, then aligns their reproductive organs and inserts his 16 00:01:03,240 --> 00:01:07,680 Speaker 1: clasper into her cloaca. The clasper, which in some species 17 00:01:07,720 --> 00:01:10,960 Speaker 1: is spiny and barbs that stays in place a transfers 18 00:01:10,959 --> 00:01:13,800 Speaker 1: sperm into the female, some of which may fertilize eggs 19 00:01:13,800 --> 00:01:17,880 Speaker 1: in her oviduct at that point, the male shark exits 20 00:01:17,920 --> 00:01:21,319 Speaker 1: the story, never to be seen again. The female may 21 00:01:21,360 --> 00:01:23,399 Speaker 1: mate with a few different males in order to produce 22 00:01:23,440 --> 00:01:28,119 Speaker 1: a single litter. Gestation periods for sharks vary from about 23 00:01:28,200 --> 00:01:32,280 Speaker 1: five to six months to two years. The spiny dogfish 24 00:01:32,280 --> 00:01:36,240 Speaker 1: shark has the longest gestation period known not just of sharks, 25 00:01:36,280 --> 00:01:40,200 Speaker 1: but of all vertebrates, at twenty four months. Here's a 26 00:01:40,280 --> 00:01:43,080 Speaker 1: rundown on those three different ways that sharks swim into 27 00:01:43,080 --> 00:01:47,720 Speaker 1: the world. First up, we've got viviparity, or live berths. 28 00:01:48,360 --> 00:01:52,360 Speaker 1: Viviparous sharks carry their embryos throughout the entire gestation period 29 00:01:52,560 --> 00:01:55,520 Speaker 1: and give birth to live shark pups, similar to how 30 00:01:55,560 --> 00:01:59,480 Speaker 1: mammals give birth. The embryos are attached inside the womb 31 00:01:59,600 --> 00:02:02,360 Speaker 1: with a oak sack placenta, which is how they receive 32 00:02:02,400 --> 00:02:06,880 Speaker 1: their nutrition. In some species, females also secrete uterine milk, 33 00:02:07,160 --> 00:02:11,840 Speaker 1: which provides more nutrients to the oak sac. Viviparity is 34 00:02:11,880 --> 00:02:15,400 Speaker 1: practiced by bigger species, such as blue and hammerhead sharks. 35 00:02:17,080 --> 00:02:22,120 Speaker 1: Then there's oviparity, or egg laying. Oviparous sharks lay eggs 36 00:02:22,200 --> 00:02:25,760 Speaker 1: which are protected by a tough egg case. These egg 37 00:02:25,760 --> 00:02:30,680 Speaker 1: cases are tubes sometimes called mermaids purses because they often 38 00:02:30,760 --> 00:02:34,560 Speaker 1: look like flat pouches complete with stringy ends on their corners. 39 00:02:35,080 --> 00:02:37,800 Speaker 1: They also look a little bit like ravioli or a 40 00:02:37,880 --> 00:02:41,960 Speaker 1: face mask. The female shark deposits the egg cases in 41 00:02:42,040 --> 00:02:45,280 Speaker 1: the sea in spots that are hopefully safe from predators. 42 00:02:45,919 --> 00:02:49,239 Speaker 1: For example, horn sharks leave the cases in rock crevices, 43 00:02:49,520 --> 00:02:53,160 Speaker 1: where they harden into twisted spirals that are difficult to remove, 44 00:02:53,520 --> 00:02:56,480 Speaker 1: although snails and seals have been known to break the shell. 45 00:02:57,680 --> 00:03:00,600 Speaker 1: Port Jackson sharks do the same thing, carrying the egg 46 00:03:00,639 --> 00:03:03,000 Speaker 1: cases in their mouth until they find a safe spot. 47 00:03:04,240 --> 00:03:06,880 Speaker 1: From there, the shark pup is on its own. The 48 00:03:06,919 --> 00:03:09,680 Speaker 1: embryo is nourished by the yolk in the eggsack and 49 00:03:09,840 --> 00:03:13,880 Speaker 1: choose itself out when it's fully developed. Oviparous sharks develop 50 00:03:13,919 --> 00:03:17,080 Speaker 1: more embryos per litter than other sharks, but many won't 51 00:03:17,120 --> 00:03:23,679 Speaker 1: survive due to predation. Finally, there's what's called ovoviviparity, which 52 00:03:23,720 --> 00:03:28,920 Speaker 1: is a combination of the previous two. Ovoviviparous sharks produce eggs, 53 00:03:29,040 --> 00:03:31,760 Speaker 1: but instead of laying them to hatch outside the body, 54 00:03:32,040 --> 00:03:35,840 Speaker 1: they carry the eggs inside themselves. When an egg hatches, 55 00:03:35,960 --> 00:03:39,160 Speaker 1: the shark pup continues developing inside the female shark until 56 00:03:39,160 --> 00:03:42,440 Speaker 1: it's born. For the first part of the gestation period, 57 00:03:42,520 --> 00:03:46,040 Speaker 1: the embryos receive nourishment from their yolk sack, and once hatched, 58 00:03:46,120 --> 00:03:48,920 Speaker 1: the lining of the uterus likely provides uterine milk or 59 00:03:48,960 --> 00:03:51,960 Speaker 1: some other kind of nutritious fluid, but there's never a 60 00:03:52,000 --> 00:03:57,320 Speaker 1: placenta directly connecting the embryo to its mother. In some 61 00:03:57,480 --> 00:04:01,840 Speaker 1: ovoviviparous species, embryos get a dish nutrition from eating their 62 00:04:01,880 --> 00:04:06,560 Speaker 1: siblings in the womb. Yep. The eggs in ovoviviparous sharks 63 00:04:06,680 --> 00:04:09,680 Speaker 1: hatch at different times, and the shark pups sometimes practice 64 00:04:09,680 --> 00:04:13,600 Speaker 1: what's known as intrauterine cannibalism, or eating the other eggs 65 00:04:13,680 --> 00:04:19,120 Speaker 1: fertilized or unfertilized in the womb. Only about fourteen species 66 00:04:19,160 --> 00:04:22,240 Speaker 1: are known to do this, but the best known intrauterine 67 00:04:22,240 --> 00:04:26,000 Speaker 1: cannibal is the sand tiger shark. Although the sand tiger 68 00:04:26,040 --> 00:04:29,920 Speaker 1: shark has two uteri and produces many eggs, each litter 69 00:04:30,160 --> 00:04:35,160 Speaker 1: yields just two pups, one from each uterus. That's because 70 00:04:35,200 --> 00:04:38,680 Speaker 1: as the sharks develop their embryonic teeth, they start to 71 00:04:38,720 --> 00:04:43,320 Speaker 1: eat the other embryos and any unfertilized eggs. It's survival 72 00:04:43,360 --> 00:04:47,359 Speaker 1: of the fittest until only one pup remains because of 73 00:04:47,400 --> 00:04:50,160 Speaker 1: their pre birth diet. The sand tiger pups and to 74 00:04:50,240 --> 00:04:53,640 Speaker 1: the world bigger than other pups. They measure approximately three 75 00:04:53,680 --> 00:04:58,000 Speaker 1: feet or a meter long. The number of shark pups 76 00:04:58,040 --> 00:05:01,039 Speaker 1: in a litter varies among species, even among the three 77 00:05:01,080 --> 00:05:04,280 Speaker 1: main categories. The viviparous blue shark has been known to 78 00:05:04,320 --> 00:05:06,560 Speaker 1: give birth to one hundred and thirty four pups in 79 00:05:06,600 --> 00:05:09,880 Speaker 1: one litter. The whale shark has given birth to three hundred, 80 00:05:10,480 --> 00:05:15,000 Speaker 1: but such high numbers are rare. However, whether hatched from 81 00:05:15,040 --> 00:05:18,200 Speaker 1: an egg or born live, shark pups emerge as miniature 82 00:05:18,279 --> 00:05:21,200 Speaker 1: versions of the sharks they may become, which is a 83 00:05:21,200 --> 00:05:24,160 Speaker 1: good thing because they receive no further assistance from their 84 00:05:24,200 --> 00:05:28,640 Speaker 1: parents after they're born or hatched. A shark pup's success 85 00:05:28,680 --> 00:05:31,400 Speaker 1: in life is largely determined by its size of birth 86 00:05:31,680 --> 00:05:34,600 Speaker 1: and whether the female shark has used a nursery area 87 00:05:34,920 --> 00:05:37,040 Speaker 1: that is a shallow part of the sea with fewer 88 00:05:37,120 --> 00:05:40,840 Speaker 1: predators than the open sea. A Some shark species grow 89 00:05:40,960 --> 00:05:43,640 Speaker 1: very slowly, putting them in danger of being eaten by 90 00:05:43,640 --> 00:05:47,960 Speaker 1: bigger sharks for longer. If few pups survive to reach 91 00:05:48,040 --> 00:05:52,160 Speaker 1: maturity and to reproduce themselves, whether due to natural predators, 92 00:05:52,279 --> 00:05:55,520 Speaker 1: a lack of food, or other pressures like human interference, 93 00:05:55,920 --> 00:06:00,719 Speaker 1: their species could become endangered. That's why scientists are researching 94 00:06:00,800 --> 00:06:04,280 Speaker 1: how sharks reproduce and give birth, and are even experimenting 95 00:06:04,279 --> 00:06:08,680 Speaker 1: with artificial wombs four species of concern. The idea is 96 00:06:08,720 --> 00:06:12,640 Speaker 1: that when fishers accidentally catch and kill pregnant sharks, the 97 00:06:12,720 --> 00:06:15,719 Speaker 1: living embryos could be rescued and brought to term in 98 00:06:15,880 --> 00:06:21,000 Speaker 1: these human made environments and then hopefully released into the wild, or, 99 00:06:21,240 --> 00:06:23,480 Speaker 1: in the case of those sand tiger sharks, a few 100 00:06:23,480 --> 00:06:26,400 Speaker 1: embryos could be rescued from the pup beat pop womb 101 00:06:26,680 --> 00:06:34,680 Speaker 1: to develop in solitary safety. Today's episode is based on 102 00:06:34,680 --> 00:06:37,800 Speaker 1: the article how are shark pops Born? On HowStuffWorks dot com, 103 00:06:37,839 --> 00:06:41,320 Speaker 1: written by Molly Edmunds. Brainstuff is production of iHeartRadio in 104 00:06:41,360 --> 00:06:43,680 Speaker 1: partnership with how stuffworks dot Com and is produced by 105 00:06:43,720 --> 00:06:46,960 Speaker 1: Tyler Klang. Four more podcasts from my heart Radio visit 106 00:06:46,960 --> 00:06:49,919 Speaker 1: the iHeartRadio app, Apple Podcasts, or wherever you listen to 107 00:06:49,960 --> 00:06:50,800 Speaker 1: your favorite shows.