Latest / How To Protect The Ocean / Great White Shark Populations Have Interesting DNA

Transcript

Great White Shark Populations Have Interesting DNA · How To Protect The Ocean

• 0:00
  Today I'm gonna be talking about great white shark DNA, and
• 0:04
  you're probably wondering why.
• 0:05
  What does it matter?
• 0:05
  Because it's an enigma, it's a mystery.
• 0:09
  It's generally just weird.
• 0:11
  And we're gonna talk about why it's important to talk about how
• 0:14
  weird great white shark, DNA is and why we need to understand how
• 0:19
  it happened and what's happening.
• 0:21
  That's what we're gonna talk about on this episode of the How
• 0:23
  to Protect the Ocean Podcast.
• 0:24
  Let's start the show.
• 0:27
  Hey everybody.
• 0:27
  Welcome back to another exciting episode of the How to Protect the Ocean Podcast.
• 0:30
  I'm your host, Andrew Lewin, and this is the podcast where you find
• 0:32
  out what's happening with the ocean, how you can speak up for the ocean,
• 0:35
  and what you can do to live for a better ocean by taking action.
• 0:39
  On today's episode, we're gonna be talking about an article
• 0:41
  that came out in Science Alert.
• 0:44
  It was a really interesting article.
• 0:45
  It came out earlier in August, but it was something that I
• 0:48
  found that needed to be shared.
• 0:49
  Carly Cassella, I believe is how you pronounce it.
• 0:52
  This is part of the nature category for Science.
• 0:54
  Alert wrote this and she titled it, The DNA of Great White Sharks
• 0:57
  Defies Explanation and Here is Why.
• 1:00
  So let's talk about great white sharks.
• 1:02
  Like great white sharks, since the movie Jaws, and by the way, it's Jaw's 50th
• 1:06
  anniversary this year, back in June, have really captured the minds and the
• 1:10
  fears of humans all around the world.
• 1:13
  It captured it so much that after people watching Jaws, including myself,
• 1:16
  I was a kid when I watched Jaws.
• 1:18
  I was probably nine or 10 when I first watched it.
• 1:20
  I had trouble swimming in pools.
• 1:22
  I had trouble swimming in lakes.
• 1:24
  I always thought like, there's a great white in my bathtub
• 1:26
  potentially.
• 1:27
  The imagination of sharks and what they could do and where they could
• 1:30
  go after watching Jaws was amazing.
• 1:34
  They became feared quite a bit.
• 1:35
  It also spurred a lot of funding to find out more about great white sharks,
• 1:41
  and we have learned a lot because the funding has been there, researchers
• 1:45
  have been there, and if you listen to Beyond Jaws in any point in time,
• 1:48
  you know that there is literally a generation of scientists that we coined
• 1:52
  the jaws generation because that's how they cut their teeth so to speak, no pun
• 1:57
  intended, within the shark science world.
• 1:59
  And they learned a lot more, not only about great whites,
• 2:02
  but a lot of other sharks.
• 2:04
  but it is different.
• 2:05
  Like great white sharks are built different and they're a great
• 2:09
  conservation success story, not only on the west coast, but also
• 2:12
  on the east coast of North America.
• 2:14
  And we're seeing more and more and we're seeing them, just, I guess, lengthen or
• 2:19
  increase their distribution every day.
• 2:22
  Now we're starting to see more and more great white sharks in Nova Scotia,
• 2:25
  which was a rare sighting, just a few, like five or six years ago.
• 2:28
  I don't know if it's just 'cause we're searching more, that we have more
• 2:30
  researchers out there looking at it.
• 2:32
  But it didn't happen often.
• 2:33
  Now it's happening this summer seems to be the summer of the great
• 2:36
  white shark over in Nova Scotia, and we've learned a lot about this,
• 2:38
  especially with tracking sharks.
• 2:40
  We've learned about where they go.
• 2:42
  We've learned about the different populations, and that's
• 2:44
  where this article comes in,
• 2:46
  It used to be before the Ice age 10,000 years ago, there was one population
• 2:50
  of great white sharks, genetically.
• 2:52
  That's what it was.
• 2:53
  Now there's a distinct three groups that have emerged.
• 2:57
  So one in the North Pacific, one in the South Pacific in Indian Ocean, and one
• 3:01
  in the North Atlantic and Mediterranean.
• 3:03
  So this is intriguing to say the least, right?
• 3:07
  Because you know, the genetic evidence suggests that these groups
• 3:10
  all stem from a single population that survived the Ice Age.
• 3:13
  So 10,000 years ago before spreading into today's three different groups.
• 3:17
  Yet, despite knowing these genetic divisions exist, mitochondrial DNA and
• 3:23
  nuclear DNA do not line up, meaning that the common explanations like
• 3:28
  migration and breeding patterns
• 3:29
  aren't enough to explain the three different groups.
• 3:32
  So the mystery remains unsolved and so this is what you kind of need to know.
• 3:37
  Before we get into trying to explain what's been happening.
• 3:41
  You might be wondering why we care about a genetic mismatch.
• 3:44
  You know, understanding population structure is essential for conservation.
• 3:48
  So population resilience.
• 3:49
  So genetic diversity helps population adapt to change.
• 3:53
  the more diverse you have populations, so the genetic diversity of
• 3:57
  each population matters, right?
• 3:59
  Because if you lose one population, you'll still get another population.
• 4:02
  'cause the genetic differences might be the reason why that population survives.
• 4:07
  So for instance, if you have two shark populations with different genetic
• 4:10
  makeups and there's one population that just can't find, like say it
• 4:14
  has a food that it really likes one day and that food disappears, then,
• 4:18
  you know, you lose that population.
• 4:20
  But the other population that's genetically different has the ability
• 4:23
  to be able to say, Hey, you know what, I can eat a bunch of different
• 4:27
  things so I don't have to worry about this population that's gone, but
• 4:30
  you still have a great white there.
• 4:31
  So having that genetic differences, whatever reason, a population disappears,
• 4:35
  whether it's food, whether it's an ice age, whatever that might be.
• 4:38
  this is really important to stabilize the overall species.
• 4:42
  It's exactly how a lot of the zoos and aquariums are founded on the basis
• 4:46
  that they're founded on, and how their breeding programs work to ensure that
• 4:49
  they preserve the genetic diversity of a species in order to ever, they have to,
• 4:55
  bring those back to the wild to repopulate and to stabilize the
• 4:59
  species that may have been just degraded of their species, diversity
• 5:04
  in the wild for one reason or another.
• 5:06
  So having that resilience is really important.
• 5:09
  Genetic diversity is such an important aspect of biodiversity
• 5:12
  and just conservation management and also management planning.
• 5:15
  If distinct groups exist, protections must be tailored to each of those regions.
• 5:20
  Not a one size fits all sort of area.
• 5:22
  So the genetic differences might require unique management approaches, and that's
• 5:27
  gonna be important in conservation.
• 5:29
  And then of course, there's the threat assessment.
• 5:30
  Knowing how populations intermix helps us track human impacts, climate effects
• 5:35
  as well as fishing pressure and more.
• 5:38
  So this is something that's really important.
• 5:40
  So basically, in short, resolving the DNA mysteries gives us the
• 5:44
  tools to better protect great whites and the ecosystems they anchor.
• 5:48
  You have to remember that.
• 5:50
  When a great white is in the mix of a population of a food web, it
• 5:53
  controls that food web a lot of the times, unless there's orcas around.
• 5:56
  But when you see the disappearance of great whites, whether it be
• 5:59
  'cause of orcas or whether it be 'cause of phishing pressure or lack
• 6:02
  of food, it changes the makeup of a food web, which changes the entire
• 6:06
  ecosystem, whether it be for good or for bad, depending on what you consider good
• 6:10
  and bad in an area, but it makes change.
• 6:12
  So ensuring that these populations stay intact and make sure that we have
• 6:16
  conservation measures to make sure these great whites are there, then it
• 6:19
  makes a difference even as great whites move into new ecosystems because of
• 6:23
  climate change, warmer waters, or the fact that they're trying to get away
• 6:25
  from competition and extend their range
• 6:28
  that also matters in terms of how we conserve a specific area.
• 6:32
  'cause a number of great whites showing up within an ecosystem will change
• 6:34
  that food web of that ecosystem and change the predator prey dynamics.
• 6:37
  That's really important.
• 6:39
  So it's a big thing of why it matters, right?
• 6:41
  It's something that we need to know.
• 6:43
  But let's get back into the genetic puzzle because like diving into this article,
• 6:48
  they're wondering, how does this happen?
• 6:50
  How do we see differences in mitochondrial DNA and or nucleus DNA?
• 6:54
  that's a big thing.
• 6:55
  And we're gonna get into a bit of science here, but I think it's
• 6:57
  important to understand the difference between the different DNA, right?
• 7:02
  Because that's something that's really important.
• 7:04
  So nuclear DNA is packaged inside the nucleus of a cell.
• 7:07
  So that's why it's called nuclear DNA, hence the name, right?
• 7:11
  But mitochondrial DNA is packaged inside the mitochondria, which
• 7:15
  turns out energy out for the cell.
• 7:17
  So very different sort of functions of mitochondrial DNA and nuclear DNA.
• 7:22
  So unlike nuclear DNA, this is quoting from the article, which is inherited
• 7:26
  from both parents, mitochondrial DNA is thought to be inherited from the mother
• 7:31
  in most multicellular animals, sharks included.
• 7:35
  So because mitochondrial DNA can trace a maternal line, conservation biologists
• 7:41
  have used it for years to identify population boundaries and migration paths.
• 7:46
  So what that looks like is that, when you start to look at how, especially
• 7:50
  sharks, some sharks, the mothers will go back to the place where they bred last.
• 7:55
  So it's called philopatry.
• 7:57
  I don't know if I'm pronouncing it, this is a new term for me, but essentially what
• 8:00
  happens is the mother will go back to the same place and will mix DNA with the male
• 8:05
  and then will put out some offspring.
• 8:07
  That is important to tracing where things are going.
• 8:10
  But however, when it comes to great whites, the method isn't working.
• 8:14
  So even after using one of the largest data sets of great white
• 8:16
  sharks globally, researchers have come up like empty handed.
• 8:21
  So previously scientists suspected that changes in the mitochondrial DNA
• 8:24
  were due to female sharks returning to the birthplace to reproduce a concept
• 8:28
  known as females philopatry, I think I'm pronouncing that properly, but
• 8:31
  the hypothesis is even supported by the recent observational evidence, which
• 8:35
  suggests that while both male and female sharks travel vast distances, females
• 8:40
  return home when it's time to mate.
• 8:42
  When the researchers and one of the main researchers of Gavin Naylor and
• 8:46
  colleagues put that into the idea, to the test, however, it failed to
• 8:49
  explain the groups of mitochondrial DNA.
• 8:52
  So the sequencing of 150 great white sharks from around the world,
• 8:56
  the sequencing of the genes, Naylor and his team found no
• 9:00
  evidence of female philopatry.
• 9:02
  A small signal would be expected in nuclear DNA if females were the only
• 9:07
  breeding within certain populations.
• 9:09
  But that wasn't reflected in the nuclear data at all.
• 9:12
  So even when the team ran an evolutionary simulation showing how sharks might
• 9:16
  have split off into three groups since their last shared ancestor, it came
• 9:21
  up that the hypothesis didn't stand.
• 9:22
  Gavin Naylor's quote is, I came up with the idea that sex ratios might
• 9:26
  be different that just a few females were contributing to the populations
• 9:30
  from one generation to the next.
• 9:31
  So like only a few females were reproducing.
• 9:34
  That also failed to explain the genetic differences so did random
• 9:37
  genetic changes that accumulate over time called genetic drift.
• 9:41
  There's a really cool graphic here looking at divergence of great white lineages.
• 9:45
  So I highly recommend that you click the link in the
• 9:46
  description to get the article.
• 9:48
  Because they're looking at, you know, divergence of great white sharks
• 9:51
  lineages based on genome sequencing, it's really cool 'cause you see
• 9:54
  how there are some DNA that's mixed into these different populations and
• 9:58
  sometimes it just doesn't make sense.
• 10:00
  The team argues that an alternative evolutionary mechanism
• 10:03
  must necessarily be operating.
• 10:04
  So there's something else going on here.
• 10:06
  Right, and so, but the only other known explanation is the natural selection may
• 10:11
  have honed in each group's mitochondrial DNA, and that seems pretty far fetched.
• 10:16
  So there are only 20,000 great white sharks in the world, which
• 10:20
  is a very small population.
• 10:22
  Relatively speaking, when you look at other species,
• 10:25
  if there's something beneficial in the evolution of some forms of mitochondrial
• 10:28
  DNA, then it would have to save the sharks from something brutally lethal.
• 10:32
  This is what Gavin's saying, Gavin Naylor.
• 10:34
  So Gavin has doubts that this is the case, like some piece of
• 10:38
  the puzzle is clearly missing.
• 10:40
  As he says, the mitochondrial DNA observed in natural populations
• 10:44
  was never reproduced in any of the simulations, even under extreme phenol
• 10:48
  philopatry, suggesting that other forces have contributed to the discordance.
• 10:53
  Right.
• 10:53
  So the same approach would benefit other species of shark where female
• 10:57
  philopatry has previously been assumed based on genetic data.
• 11:00
  So there's a lot of mystery around here, which we don't even know
• 11:03
  why this is happening, right?
• 11:04
  We just don't understand it.
• 11:06
  But to understand the DNA could be a key to unlocking how to manage great white
• 11:12
  sharks properly and how to manage other species that might show the same thing.
• 11:16
  You know, there are other sharks that have similar philopatry,
• 11:19
  like female philopatry.
• 11:21
  Some of them include uh, I'm just looking here.
• 11:23
  I have a list.
• 11:24
  Lemon sharks, blacktip sharks, sandbar sharks, tiger sharks, nurse
• 11:28
  sharks, reef associated sharks, like, whitetip reef sharks.
• 11:31
  That's a huge thing.
• 11:32
  And you are probably wondering why does it matter?
• 11:34
  'cause returning to specific popping grounds means that the protection
• 11:38
  of small critical nursery habitats can safeguard generations of sharks.
• 11:42
  So just having a marine protected area in a popping zone, that is
• 11:45
  huge to protecting these sharks.
• 11:47
  Of course, keeping the genetic structure.
• 11:49
  So philopatry leads to distinct subpopulations, making localized
• 11:53
  overfishing more damaging.
• 11:54
  So being careful of that and management using marine protected areas must consider
• 11:59
  these natal sites to be effective.
• 12:01
  So when we actually look and we want to make sure that everything is protected,
• 12:06
  we can look at these smaller sites and say, Hey, this is a popping zone.
• 12:09
  We know this is a popping zone because these sharks keep coming back
• 12:12
  to this area, these female sharks.
• 12:14
  This is important.
• 12:15
  We have to protect this.
• 12:16
  This is a very important area.
• 12:18
  If the sharks get fished during this time, it's gonna destroy
• 12:20
  the population eventually.
• 12:22
  So that's something that's very important as well.
• 12:24
  So that's where we're gonna leave it.
• 12:26
  It's really just a mystery.
• 12:28
  It's weird.
• 12:29
  Great white shark DNA is weird.
• 12:31
  And we have to understand that we're gonna need more research to find out why
• 12:35
  it's so weird and how to explain these diversions into these three groups.
• 12:40
  Very interesting article.
• 12:41
  Something that I want to share with you.
• 12:43
  So if you have any questions or comments, please let me know in the comments.
• 12:47
  If you're watching this on YouTube or you want to get ahold of me,
• 12:50
  there's a number of different ways.
• 12:51
  You can go to Instagram at How to Protect the Ocean.
• 12:53
  Just message me.
• 12:54
  You can go to speak up for blue.com/contact.
• 12:57
  Just fill out the form, goes to my email, or you can hit me up on TikTok.
• 13:01
  Just DM me, at speak Up for Blue.
• 13:03
  I wanna thank you so much for joining me on today's episode of the
• 13:05
  How to Protect the Ocean Podcast.
• 13:06
  I'm your host, Andrew Lewin from the True Nordstrom and Free.
• 13:09
  Have a great day.
• 13:10
  We'll talk to you next time and happy conservation.