Bats in Technicolor: The Evolution of Color Vision by Gene Loss • iBiology

00:00:10.08 Have you ever wondered what animals can see,
00:00:11.29 like your cat or your dog?
00:00:14.29 Or a fish that lives underwater?
00:00:17.19 Or a bat that flies in complete darkness?
00:00:20.13 Or even an eagle that has to catch
00:00:23.02 a teeny tiny mouse on the floor?
00:00:24.28 Do they see the same thing as you do,
00:00:26.21 or do they have a vision adapted
00:00:28.18 to where they live, what they eat…
00:00:30.13 in other words, their environment?
00:00:32.26 I’m Alexa Sadier, a research scientist at UCLA,
00:00:35.06 and this is the kind of question I am interested in:
00:00:37.09 what animals can see and how their vision evolves
00:00:40.11 in adaptation to where they live,
00:00:42.03 and how can find big evolution principles
00:00:44.29 by using these results.
00:00:47.28 And you might be surprised
00:00:49.01 if I tell you what I study,
00:00:50.13 because I don’t study all the animals in the world
00:00:52.14 to answer this question.
00:00:53.27 I’m studying a group that is diverse enough
00:00:56.10 so we have a lot of different species
00:00:58.19 that live in a lot of different kinds of environment
00:01:01.05 and eat a lot of different things.
00:01:03.11 And this group is bats.
00:01:06.08 And you might be surprised,
00:01:07.26 because people have so many misconceptions about bats.
00:01:10.07 But they are also indeed really diverse
00:01:12.09 and have everything we are interested in.
00:01:14.24 So, first, diversity — just look at them.
00:01:17.27 Some of them are red, some of them have big ears,
00:01:20.17 some of them have a lot of different colors.
00:01:23.07 So, just by looking at these species I’m showing you here,
00:01:26.24 you see how incredibly diverse they are.
00:01:29.10 But even that is just a subset.
00:01:32.21 It’s only 30 species.
00:01:34.07 That is a small subset of the 1426 bat species
00:01:37.02 that we have in the world,
00:01:38.25 which is 1/5 of mammals.
00:01:41.02 And as I said, we’re interested in vision.
00:01:43.17 We are interested in what animals can see.
00:01:46.06 And if you look at these bats again,
00:01:48.13 you can see that we have the diversity in terms of vision as well.
00:01:51.09 I mean, in terms of their eye size,
00:01:54.04 some of them, like this fruit bat,
00:01:55.29 have very, very big eyes
00:01:58.27 that are very, very big compared to his head.
00:02:01.27 But others have eyes so tiny
00:02:04.16 that we can barely see them.
00:02:06.09 And if you look at the other bats,
00:02:08.08 you can see that we have a lot of different eye types —
00:02:09.29 different colors, etc, etc.
00:02:12.23 As everywhere in science, every time,
00:02:15.09 we start with an observation.
00:02:16.23 And by looking at these bats,
00:02:18.04 we can see that we have this diversity of eye types,
00:02:20.21 so maybe we have a diversity of vision.
00:02:23.25 And maybe this is because these bats
00:02:25.24 are adapted to their environment.
00:02:27.08 So, where do they live?
00:02:29.15 Because if they are adapted to their environment,
00:02:31.04 they might live in different places.
00:02:33.20 And so, to do that, let me show you these maps.
00:02:35.28 So, you can see that we have bats almost everywhere in the world,
00:02:38.22 except in the polar regions, where it’s white.
00:02:42.17 And this map also tells us something else:
00:02:44.20 the color of the map
00:02:46.14 shows us the number of species of bats you can find.
00:02:49.03 So, when it’s red and yellowish,
00:02:50.23 it means that you have a lot of bat species here.
00:02:53.16 So, if we are interested in looking at vision evolution in
00:02:58.02 a lot of different bat species,
00:03:00.02 of course we want to go where we have a lot of bat species,
00:03:02.07 which is in the reddish and yellowish regions,
00:03:04.24 meaning that when I want to study bats,
00:03:06.20 I go to the tropics.
00:03:08.22 And here in yellow you can see
00:03:12.00 the different field sites that we have.
00:03:13.19 So, we go to the Caribbean, here,
00:03:15.24 to the island and the mainland.
00:03:17.12 We also go to Africa, here, in Cameroon,
00:03:20.03 a tropical area as well.
00:03:21.20 And we also go to the Philippines.
00:03:24.06 And if you are not convinced
00:03:26.08 that just by going there we are hitting a lot of different environments,
00:03:29.16 let me bring you into the field
00:03:31.09 so you can see how it looks like.
00:03:33.21 For example, when we go to Belize,
00:03:36.02 we go to these wonderful, magnificent forests
00:03:38.27 that are really dense,
00:03:40.27 and bats roost in these forests.
00:03:42.07 But as you can see here,
00:03:43.25 we also have some Mayan temples,
00:03:45.07 so it’s really, really exciting.
00:03:47.04 It’s kind of Indiana Jones-style field work,
00:03:49.22 because bats also roost sometimes
00:03:51.26 in some of these temples that are not excavated,
00:03:54.11 so we have one area here.
00:03:56.20 When we go to Puerto Rico,
00:03:58.12 we also see some big deep jungle forests,
00:04:01.02 and we have different species of bats here, compared to Belize,
00:04:04.12 which is a mainland.
00:04:05.24 So, we have another type of habitat,
00:04:07.11 which is the island forest here in Puerto Rico.
00:04:10.25 When we go to Puerto Rico, again,
00:04:13.12 in other places, we have some cave habitats.
00:04:15.25 So, it’s another type of habitat here —
00:04:17.25 a cave, a deep cave, where we find bats as well.
00:04:20.09 And finally, when we go to other places,
00:04:23.07 such as Trinidad, we have caves…
00:04:25.02 we have caves underwater, and we have forests,
00:04:27.03 but we also have houses
00:04:29.16 in which we have some bats that fly.
00:04:32.17 So, just by going into these different places,
00:04:35.04 we have all these different habitats where bats live,
00:04:37.24 and so then we can study how their vision
00:04:39.21 is adapted to that.
00:04:41.03 But as I said, something we can consider as well is food to see…
00:04:44.26 if bats are so adapted to where they eat…
00:04:47.19 because they are foraging,
00:04:49.02 they need to see what they eat very well.
00:04:51.17 And just by going there and catching bats there,
00:04:53.17 we also have the full different range of diets that bats can have.
00:04:56.22 For example, if you look at this picture here,
00:05:00.12 when I catch some bats, I can…
00:05:02.14 I can understand what they eat.
00:05:04.03 If I catch one bat that had this very, very elogated snout
00:05:06.23 that you see here,
00:05:08.19 and if this bat is also covered with pollen,
00:05:10.12 it’s likely to be a plant bat.
00:05:12.23 The other bat you can see here is
00:05:15.14 the vampire bat that eats blood.
00:05:17.19 I caught this one on a chicken on a tree,
00:05:19.19 and as you can see,
00:05:21.20 some of the fingers of that bat are covered with blood,
00:05:23.16 and also its face.
00:05:25.03 It’s because it’s a vampire bat that eats a lot of blood.
00:05:27.27 Now, you can see as well that
00:05:30.14 we can catch some insect bats that fly at night
00:05:32.14 and are catching a lot of insects.
00:05:34.12 We can also find some fish bats,
00:05:36.28 because some bats are fishing.
00:05:39.04 And so, you can see on this picture a bat
00:05:41.25 just arriving and catching a fish in the water.
00:05:43.19 We also have bats that eat animals,
00:05:45.03 omnivorous bats,
00:05:46.29 and we also have bats that eat fruit.
00:05:49.09 This is a teeny tiny fruit bat
00:05:51.05 that I caught in the forest,
00:05:52.25 and sometimes before releasing them we just give them a little snack.
00:05:56.02 This one is from Belize.
00:05:58.09 Okay, so, by looking at these different places
00:06:01.04 and these different bats and the diversity,
00:06:03.14 can we now ask the question we want to ask in this talk?
00:06:07.29 So, the first question that we had is, what do bats see?
00:06:10.20 Do they see a lot of different things?
00:06:12.15 Do they all see the same?
00:06:14.00 We don’t know.
00:06:15.15 So, what do they see?
00:06:16.29 And we have seen that they live in a lot of different places
00:06:19.00 and eat different things.
00:06:20.18 Does their vision relate to where they live
00:06:22.17 and what they eat?
00:06:24.11 Do we have an adaptation to these different lifestyles and environments?
00:06:28.10 And finally, the other question we can ask is,
00:06:31.04 what can this tell us about the evolution of species
00:06:33.21 in general?
00:06:35.12 Do… can we find big, big, big principles
00:06:37.24 just by studying bat vision
00:06:39.15 that will be applicable to a lot of different kind of things?
00:06:42.10 So, before digging into the results,
00:06:44.22 I just want to give you a little primer about how do bats,
00:06:47.28 in general, and mammals see.
00:06:49.29 So, bats see through their eyes.
00:06:51.24 So, it’s exactly like us.
00:06:53.12 The light just hits the eye,
00:06:56.18 and it hits the back of the eye.
00:06:58.14 And it’s very important to understand that because at the…
00:07:00.24 in the back of the eye, we have the retina,
00:07:02.27 which is the tissue which is sensitive to light.
00:07:05.25 And in this tissue, how do…
00:07:07.14 how does this tissue sense light?
00:07:09.13 It senses light through photoreceptors,
00:07:12.05 the rods and the cones, in green and blue here.
00:07:14.24 And these photoreceptors are the cells
00:07:16.26 that are able to sense the light
00:07:19.03 and to relay these light messages
00:07:21.14 through a couple of cells and neurons into the brain.
00:07:23.19 That will reconstitute the images.
00:07:26.07 As I said, we have two types of photoreceptors.
00:07:28.14 Why? Why do we have two types?
00:07:30.19 We have two types because they are sensitive
00:07:32.17 to different types of light.
00:07:34.12 First, we have the rods that are sensitive to very, very dim light,
00:07:38.08 so they allow us to see during the…
00:07:41.02 you know, the… at night or in…
00:07:43.20 kind of a darkness, with very, very low light.
00:07:46.10 And we have only one type of that photoreceptor,
00:07:48.22 one type of rod.
00:07:50.15 So, that’s why we see in black and white.
00:07:52.13 During the day and when the light is, like,
00:07:55.10 you know, at dusk and dawn, so low light,
00:07:57.05 we have the cones that are active.
00:08:00.03 And we have three types of cones,
00:08:01.27 and they allow us to see in all the different colors
00:08:04.26 of the visible spectrum.
00:08:06.29 How?
00:08:08.10 So, we have some red cones, green cones, and blue cones.
00:08:10.15 And if you don’t understand why having three types of cones
00:08:13.08 allows us to see the different colors of the visible spectrum,
00:08:15.22 just think about your computer screen,
00:08:18.29 or if you try to modify a picture on your screen.
00:08:22.22 You always play with the red, the green, and the blue channels,
00:08:25.19 and by changing the amount of color that you have,
00:08:28.00 you are able to reconstitute the different colors that we see.
00:08:31.14 It’s the same as our brain…
00:08:33.26 it’s… our brains do that in humans.
00:08:35.15 We have a red cone and blue cone and a green cone,
00:08:38.18 and by playing with the different intensity of these cones,
00:08:40.16 we are able to reconstitute the colors of the rainbow.
00:08:43.11 And for the rest of the talk, and for the bats here,
00:08:45.21 we will focus on the cones.
00:08:47.16 So, we won’t focus on the bat vision in general,
00:08:50.29 but we will focus on color vision in bats.
00:08:53.23 So, what do bats see?
00:08:55.11 Do they also have red/green/blue like us?
00:08:57.15 Actually not.
00:08:59.12 The studies that had been done on bat color vision
00:09:03.14 and on cones, etc,
00:09:05.12 have revealed that bats have…
00:09:07.15 seem to have two types of photoreceptors:
00:09:10.02 S cones and L cones.
00:09:12.01 S cones are responsible for UV light vision.
00:09:15.09 So, a lot of bats can see UV.
00:09:17.10 And L cores are responsible for greenish light vision.
00:09:21.07 So, what we think…
00:09:23.11 these studies have been done on a very small set of bat species,
00:09:25.25 only ten-ish bats… species of bats…
00:09:29.23 have shown that maybe the ancestor of all bats
00:09:32.03 had UV and green vision,
00:09:34.14 and that maybe some bats have lost some vision.
00:09:36.29 But of course, when you think that we have
00:09:38.24 1426 species of bats,
00:09:40.25 we don’t really know at all how they evolved
00:09:42.23 in a lot of different things.
00:09:44.03 So, this is what we tried to look at here.
00:09:46.25 But in fact, what does it mean
00:09:49.20 for the bats to have only two types of cones for color vision?
00:09:52.09 This is a picture how we will see it
00:09:54.05 with three different cones.
00:09:55.24 And this is what bats would see
00:09:57.24 with two different colors.
00:09:59.13 So, they would see something that would be
00:10:01.22 kind of close to what colorblind people would see,
00:10:05.02 people that lack the red cone in humans.
00:10:08.09 So, they would see that.
00:10:09.24 So, of course, if you think about being a bat and seeing this,
00:10:11.25 you can see that it can have some implication
00:10:14.19 in how you will discriminate food in the foliage, etc,
00:10:18.00 and if you lose one of the two cones,
00:10:20.03 you will see basically black and white.
00:10:21.29 So, a better understanding of color vision at this point
00:10:25.17 for a bat — from the point of view of the bat
00:10:27.10 and also from the point of view of evolution —
00:10:29.08 can, you know, help us to understand what’s going on.
00:10:32.05 So, how will we study the presence or absence
00:10:35.21 of these cones and the color vision?
00:10:37.08 How will we do that in the lab, concretely?
00:10:40.24 So, we won’t focus on the cone themselves,
00:10:42.24 but we will focus on the pigments that send light into the cone.
00:10:45.29 If you remember what I said before,
00:10:47.20 the cones are able to sense light
00:10:50.04 and to relay the signal into the brain.
00:10:52.09 And this is done through two types of proteins.
00:10:55.00 The opsins… those are the pigments…
00:10:57.22 the protein that sends light inside the cone.
00:11:00.06 We have two of them:
00:11:02.06 the S opsins that are responsible to sense UV light
00:11:04.16 — in the S cones, you have S opsins —
00:11:06.14 and the L opsin that is responsible
00:11:08.28 to sense green light — in the L cones, you have green opsins.
00:11:11.16 And we won’t only study the presence of these proteins in these bats;
00:11:15.12 we will al… we will study the presence of these opsins
00:11:18.17 at the three levels of gene regulation
00:11:20.11 that we can have.
00:11:21.24 We’ll study the presence of the genes,
00:11:23.11 the S opsin gene and the L opsin gene,
00:11:25.13 in the genome of a lot of bats.
00:11:27.14 We will see if this gene is expressed
00:11:29.24 by checking for the presence or absence of the RNA
00:11:31.26 of these genes.
00:11:33.09 And we will also check if a protein is produced at the end.
00:11:35.20 So, do we have S opsins and L opsins
00:11:38.02 to make an S cone and an L cone?
00:11:40.07 So, keep that in mind; it’s really important.
00:11:42.12 We will study all these three levels of regulation here.
00:11:45.26 Okay, so how will we do that in the lab?
00:11:48.12 How will we study these three levels of regulation?
00:11:51.29 So, to do that, we will do that on
00:11:53.28 55 species of bats that span the variation in terms of environment
00:11:57.01 and the variation in terms of the diet
00:11:59.13 that we can find in these bats.
00:12:01.12 And we did that in field species,
00:12:03.02 so, in species that we caught in the wild,
00:12:04.24 but also using museum specimens,
00:12:06.18 for the protein at least,
00:12:08.28 and I will talk a little bit more about that in a minute.
00:12:13.04 And so… let’s start with the protein first.
00:12:15.20 How do we study the protein?
00:12:17.28 So, to do that, we take the whole eye
00:12:20.13 of the field species or the museum species,
00:12:25.11 and we carefully dissect this eye
00:12:27.23 to have access to the retina.
00:12:29.16 So, remember, the retina is at the very back of the eye,
00:12:31.27 so we open the eyes,
00:12:33.28 and we have access to this tissue, the retina,
00:12:36.01 in the back, where we can find the photoreceptors,
00:12:38.13 where we can find the cones,
00:12:40.08 and so the opsins.
00:12:42.06 And on this retina, we then use an antibody
00:12:44.06 that will recognize specifically either
00:12:46.22 the L opsins or the S opsins.
00:12:49.20 And just by putting this antibody on the retina,
00:12:51.29 we’re able to see if we have or not
00:12:55.04 the S cones and the L cones.
00:12:57.02 How?
00:12:58.15 Because the antibody will recognize specifically the opsins,
00:13:00.04 and when you have a lot of opsins in a cone,
00:13:01.24 you will have a dot, here,
00:13:03.10 that you see in green for, here, the L cones.
00:13:06.12 And so, just by doing that,
00:13:08.14 we are able to see the presence or absence
00:13:09.29 of the cones in these bats.
00:13:11.22 And we have done that on field species,
00:13:13.09 so in species we caught in the wild,
00:13:15.04 through this dissection, but also,
00:13:16.26 which is kind of pretty cool,
00:13:19.02 on museum specimens.
00:13:20.07 And some of them are really, really old,
00:13:22.28 like a hundred years old — older than us.
00:13:24.18 Which is super interesting
00:13:26.21 because it just shows us that we don’t necessarily need to go into the field
00:13:29.22 and catch species where they are
00:13:32.13 and, you know, use wild animals to do this kind of study,
00:13:34.16 but we can also use museum specimens,
00:13:38.12 which just shows us how important museums are
00:13:40.17 and what resources we can get from these museums.
00:13:44.17 So, this is what we do for the protein detection.
00:13:46.12 How do we detect the RNA,
00:13:48.15 the mRNA, so the expression of the opsin gene?
00:13:52.24 So, to do that, we take the whole eye of a bat
00:13:54.28 and we sequence all the mRNA
00:13:57.23 coming out of these eyes.
00:13:59.17 And we were looking for the presence
00:14:01.27 of the L opsins and the S opsins
00:14:03.23 in this subset of mRNA that we have in the eyes.
00:14:07.07 And finally, we look at the presence or absence
00:14:11.03 of the S opsin and the L opsin genes
00:14:15.28 by PCR and sequencing in the genome,
00:14:17.16 because for a lot of these bats…
00:14:19.07 of course, this is a non-model species,
00:14:21.01 so we don’t have the genome.
00:14:22.13 We have the genome of only a few of them,
00:14:24.12 and we’ll probably have more genomes in the future,
00:14:26.12 but right now we just can’t just go on the database
00:14:29.02 and look for a gene on the genome
00:14:30.26 because it’s just not there.
00:14:33.10 Alright.
00:14:35.12 So, we have the setup to study protein, mRNA, and DNA.
00:14:40.26 So, what are the results?
00:14:42.19 What do bats see?
00:14:44.12 So, let’s start with the protein first.
00:14:46.06 What can these flower-shaped retinas…
00:14:49.28 what is the study of… the protein can tell us about bat vision?
00:14:53.29 It can tell us a lot more than just the presence or absence, actually.
00:14:58.11 So, we have these flower-shaped retinas.
00:15:00.24 Here, you have an example of an insect species,
00:15:03.22 and we were looking for the presence
00:15:05.10 of the L cones and the S cones.
00:15:06.24 As you can see from this species,
00:15:08.20 we have the presence of the L cones and the S cones
00:15:12.19 — we can see the dots for both things —
00:15:14.27 but it’s not the only thing we can see.
00:15:16.17 By looking at that, you can also see that we can assess
00:15:18.12 the density of the cone that we have.
00:15:21.00 Just by counting the number of dots
00:15:22.26 that we have per square millimeter,
00:15:24.27 we can see if a bat would have
00:15:27.16 more cones than another one
00:15:29.02 or if we have more L cones than S cones.
00:15:31.17 And it is very important for bat vision.
00:15:34.06 Just, again, think about your camera.
00:15:36.13 You have the number of pixels.
00:15:38.11 The more pixels you have,
00:15:40.02 the better the resolution of the camera will be.
00:15:42.12 It doesn’t translate exactly like this for vision
00:15:44.29 — of course, it’s more complicated than that —
00:15:47.03 but just keep in mind that changing the density of cones
00:15:49.15 will have kind of the same idea
00:15:52.11 as the pixels of your camera.
00:15:53.28 The vision would be different.
00:15:56.00 The things you would be able to see will be different in your brain.
00:15:58.21 And so, just by assaying the…
00:16:01.06 assessing the difference in terms of cone density
00:16:03.11 between bats will help us to understand better…
00:16:05.26 to see if bats have different vision.
00:16:08.12 So, let’s do that with a lot of different bats.
00:16:12.03 So, here you have a subset of what we have been doing
00:16:14.14 in many bats that have different diets
00:16:17.07 and that live in different environments as well.
00:16:20.01 And here, the diet is indicated with a little insect
00:16:23.10 or the flower or the food, etc.
00:16:25.28 So, the first thing we realized
00:16:27.27 is that we were able to detect
00:16:30.08 S cones and L cones in many species of bats
00:16:32.19 with different diets.
00:16:34.09 So, that’s interesting.
00:16:36.06 But then, we realized that we don’t detect S cones everywhere.
00:16:39.02 Some species have lost S cones
00:16:41.21 and so have lost UV vision.
00:16:43.04 So, here we have some species
00:16:44.27 that have the two-color vision
00:16:46.26 — so, that are able to discriminate colors —
00:16:49.02 and some species that have only L cones
00:16:51.12 — so, they are only able to see one color,
00:16:54.07 and so they probably see kind of in black and white.
00:16:57.08 So, we have these two… first, different types of bats,
00:16:59.17 which is interesting.
00:17:00.29 They don’t all see the same thing.
00:17:02.16 The other thing we can see is that
00:17:05.14 the density of cones varies a lot between species.
00:17:08.03 We have some species, here,
00:17:09.21 that have a very dark retina in the little cartoon
00:17:12.04 that I have here,
00:17:13.21 that have a high density of cones,
00:17:15.27 whereas others — like, for example, Carollia sowelli, here —
00:17:19.21 have less L cones and even less S cones,
00:17:22.22 showing that the vision capabilities between bats are different.
00:17:26.03 And this is probably because these bats
00:17:28.05 don’t need to have the same vision capabilities
00:17:30.26 to be able to forage or sense food, etc, etc.
00:17:34.15 So, we have this huge variation between bats.
00:17:36.20 It’s not fixed.
00:17:38.14 All the bats seem to be doing different things.
00:17:40.12 And we also have less S cones than L cones
00:17:42.16 when we have both,
00:17:44.01 which is again interesting, because the only pigment that we lose
00:17:46.28 is the S opsin, so we lose the S cones in some bats.
00:17:49.20 And when we have both, we also have less S cones,
00:17:51.28 meaning that maybe it’s not that important,
00:17:54.11 but it’s just something that is gained or retained
00:17:57.15 in the bats that need to have this combination
00:18:00.08 of color and to see UV vision.
00:18:03.04 Okay.
00:18:04.18 So, we lose the S cone in some bats,
00:18:06.13 and what are the mechanisms
00:18:08.21 behind the loss of the S opsin genes?
00:18:11.18 So, to do that, we will look at the conservation of the DNA,
00:18:14.05 the mRNA, and the protein
00:18:15.26 — the three levels I talked about before —
00:18:17.15 just to see if it can give us…
00:18:19.16 if it can give us some insights about…
00:18:22.14 how do we lose a trait and these genes in bats?
00:18:27.12 So, first, as I said, the L opsin genes
00:18:29.24 and the L cones are present in all bats.
00:18:32.24 They seem to be there in all bats.
00:18:34.21 And this is exactly what we see here.
00:18:36.11 We can find, in all the bats that we study…
00:18:38.28 here, it’s a subset of the 55 species of bats we study
00:18:43.02 for clarity.
00:18:45.01 And then what you can see is we indeed have a conservation of the DNA.
00:18:48.28 We have a conservation of the mRNA expression
00:18:51.16 and of the protein.
00:18:53.16 They are present everywhere in the green cones,
00:18:55.27 in the L opsin gene, which is what we expect.
00:18:57.29 Now, when we look at the S opsins,
00:19:00.17 the picture seems to be completely different.
00:19:04.02 We have a loss of the S opsin genes,
00:19:05.28 but at different levels of regulation.
00:19:09.02 So, if we look, for example, at these species,
00:19:12.12 we have what we would expect when we first think about it:
00:19:14.15 we have lost the S opsin genes.
00:19:16.29 We don’t have an expression, of course, in the mRNA,
00:19:19.11 and we don’t have the expression of the protein either.
00:19:22.07 We have a complete loss of the S opsin genes
00:19:24.13 in these species.
00:19:26.26 Now, if we look at another species,
00:19:28.11 the picture seems to be different.
00:19:30.03 We can still find the S opsin gene in the genome,
00:19:33.04 but we don’t have the expression of the mRNA,
00:19:34.28 and of course we don’t have the expression of the protein.
00:19:38.17 So, for these species, we still have the gene in the genome,
00:19:41.20 but we have lost the other levels of regulation here.
00:19:44.21 And we have another case when we can find the gene in the genome,
00:19:48.18 and the mRNA is expressed,
00:19:50.16 but we can never find our protein.
00:19:52.07 So, here, we have lost these S opsins
00:19:55.00 at another level of regulation.
00:19:56.15 We have the DNA. We can find the mRNA.
00:19:59.00 But we will never have a protein expression of the gene.
00:20:02.19 And this is really important because
00:20:05.24 just by looking at these three levels of regulation,
00:20:07.22 we’re kind of catching evolution in action.
00:20:09.29 We can see that we… when we lose a trait
00:20:12.18 — here, when we lose the S opsin —
00:20:14.21 we don’t necessarily lose everything at the same time,
00:20:17.08 and everything from scratch.
00:20:18.28 We don’t necessarily lose the gene, the mRNA, and the protein.
00:20:22.13 We have different steps where we can lose
00:20:24.19 different levels of regulation.
00:20:27.09 Now, as I said, we are trying to relate these losses
00:20:30.20 to the adaptation to environment and food.
00:20:32.23 What’s going on?
00:20:34.03 By just looking at these different species, here,
00:20:38.06 can we find a link between the loss of the S opsin
00:20:41.20 and the adaptation to different environment and food?
00:20:44.15 So, to do that, we will… we did, like,
00:20:48.10 a test to see if we can link
00:20:51.14 the diet or the roosting capabilities, the environment,
00:20:54.29 to retaining S cones or loss.
00:20:57.08 So, let me walk through this figure, here.
00:21:00.06 Here… so, we have these different conditions.
00:21:02.08 If we’re on the zero line, it means that we have
00:21:05.20 no association with retaining S cones
00:21:08.04 in these conditions.
00:21:10.04 So, for example, for cave roosting, here in blue,
00:21:12.09 we are on the zero line here,
00:21:14.18 meaning that we have no association
00:21:16.06 between retaining S cones and roosting in a cave.
00:21:19.19 On the other hand, if you look at the green
00:21:22.07 and the pink violin plots here,
00:21:24.18 we are above the line.
00:21:26.07 We are nearly at 5, here,
00:21:28.16 meaning that we have an association
00:21:30.15 between eating fruit or visiting plants
00:21:33.11 and retaining S cones.
00:21:35.04 So, it means that here we have identified clearly
00:21:37.24 that if you eat fruit or if you visit a plant,
00:21:40.29 you are more likely to retain S cones.
00:21:43.18 So, it seems that vision and the type of things that bats see
00:21:47.12 are related to diet.
00:21:50.00 It’s not absolute.
00:21:51.19 You remember I showed you also some…
00:21:53.16 a species that eats insect and has S cones,
00:21:55.18 so it means that we might have other factors,
00:21:57.17 but we don’t have enough species here to identify that,
00:21:59.20 and it also means that we need to do more studies to do that.
00:22:03.17 Okay. So, we have investigated a lot of things.
00:22:05.29 How… what to conclude about bat vision
00:22:08.04 and evolution in general?
00:22:10.03 What can we get from these results?
00:22:12.06 Well, first, these results, as I say, tell us about…
00:22:15.08 a lot about bat vision, because with this
00:22:18.06 we have identified two main types of color vision in bats:
00:22:21.13 one type of color vision that only has L cones,
00:22:24.12 and so these bats see probably in black and white
00:22:27.19 during the day;
00:22:29.08 and we have one type of vision with two types of cones,
00:22:31.22 S cones and L cones.
00:22:33.06 These bats seem to be able to discriminate colors,
00:22:35.28 but it’s not absolute.
00:22:37.19 We might have different factors,
00:22:39.25 but they might be able to discriminate color,
00:22:41.17 maybe to find food,
00:22:43.20 maybe because it helps us to see the food better —
00:22:45.16 the fruit, for example, in the foliage, etc.
00:22:48.00 So, we have these two different types
00:22:50.10 that seem to be very important and link to diet.
00:22:53.17 But as I said, it’s not absolute.
00:22:56.04 We also have insect bats
00:22:58.10 that are able to see UV.
00:23:00.01 So, how can we explain that?
00:23:01.22 Let me bring you back into the field,
00:23:03.20 because just by looking at bats in their environment
00:23:05.23 can help us to understand that.
00:23:07.23 Here, this is a video of bats that are flying at night.
00:23:12.09 So, if you just look at this video,
00:23:13.22 you can see that bats are coming out of the cave.
00:23:16.03 And this is very early at night.
00:23:17.23 We try to set up the traps early
00:23:20.14 to catch them
00:23:22.11 because we really don’t want to miss anything.
00:23:24.08 And you can see that the light is still very high in the sky
00:23:27.21 — the light level is still high —
00:23:30.02 meaning that these bats fly out of the cave
00:23:32.06 when it’s not dark out yet.
00:23:35.02 So, maybe they do need to see…
00:23:36.23 to have a better color vision,
00:23:38.09 because they fly during the day.
00:23:40.04 Now, we also have some bats that come out of the cave
00:23:43.17 when it’s really dark, and maybe these bats
00:23:45.20 don’t need to see… to have a good daylight color vision,
00:23:48.27 because the light is already very, very dim when they go out.
00:23:50.27 So, this is something we can investigate,
00:23:53.03 and the only way to investigate that
00:23:55.08 would be to study more different species.
00:23:58.27 Now, a lot of bats are also endangered.
00:24:01.12 Is it useful to really understand what bats can see
00:24:04.06 to protect them?
00:24:05.26 Actually, yes, because if you look around
00:24:08.07 where you live, for example,
00:24:10.00 you can see that we have a lot of light in the street at night
00:24:12.22 — in the parks, etc.
00:24:14.11 And of course, as you can imagine,
00:24:16.08 you have bats everywhere in the world,
00:24:18.03 so you have probably have bats around.
00:24:20.10 And so, by understanding what they see,
00:24:22.18 it can also help to protect them
00:24:25.02 to find a light that won’t affect them.
00:24:26.24 For example, we do think that red light
00:24:29.05 won’t affect bats as much as white and green light, for example.
00:24:33.21 So, we can think about how to change the light
00:24:36.15 that we have in the street, or in the parks, or in different areas,
00:24:39.20 to be better for bats and to help them…
00:24:42.15 you know, to protect them, etc.
00:24:44.27 So, we have seen a lot of things for bats.
00:24:46.29 What about evolution in general?
00:24:49.26 This study also helps us to better understand
00:24:52.11 trait loss,
00:24:54.00 because when we think about evolution,
00:24:55.24 we always think about new things that animals gain.
00:24:58.20 You know, we gain, for example,
00:25:00.21 new abilities to be underwater.
00:25:02.18 Some species gain new abilities to fly.
00:25:04.21 But we never think about how we can evolve
00:25:06.29 by losing things,
00:25:08.19 which is something that has been very important in evolution.
00:25:10.29 When you think about it, dolphins, for example,
00:25:13.03 have lost their limbs,
00:25:15.04 or cavefish have lost their eyes in the cave.
00:25:17.17 Here, we can see that bats can evolve
00:25:20.07 by losing UV vision.
00:25:21.22 And it’s another textbook example of how a species
00:25:24.21 evolved by losing something.
00:25:26.18 And our studies also show us
00:25:29.02 how we can better understand trait loss
00:25:31.16 and how to study trait loss,
00:25:33.13 because a lot of studies focus on
00:25:35.29 the morphology or only the DNA to assess trait loss.
00:25:39.03 When we have a trait that is controlled by a gene,
00:25:40.26 which is the case here for S opsins, where…
00:25:44.10 we tend to look only in the DNA to assess
00:25:46.28 the presence or absence of this trait.
00:25:49.07 But what we have shown is that we can’t only do that.
00:25:51.21 Sometimes we have the DNA
00:25:53.18 but we don’t have the protein.
00:25:55.06 Sometimes we have the RNA and we don’t have the protein.
00:25:58.00 So, our studies show that it’s important to look at
00:25:59.18 the whole process to really understand what’s going on.
00:26:02.27 And it also tells us a lot of things about possible loss and regain, etc.
00:26:07.06 Because you can imagine that if you lose only the RNA,
00:26:10.07 maybe we have a possibility to regain this trait later,
00:26:12.22 if we need to,
00:26:14.25 if we have kind of a hotspot in evolution
00:26:16.22 when we lose or we regain a trait easily.
00:26:18.24 So, just by looking at all the processes,
00:26:21.10 we’re also in a better shape to really understand
00:26:24.18 what’s going on in evolution and the possible mechanisms.
00:26:27.14 And our study also shows how important it is
00:26:30.11 to study a lot of different kind of species,
00:26:32.06 and not only one.
00:26:33.27 Because if we study only a subset of species,
00:26:35.25 we can be like, okay,
00:26:37.22 bats see in two colors,
00:26:39.15 or these species have this trait loss, etc.
00:26:41.10 And our studies show that it’s way more complex and diverse
00:26:44.12 than what we think it is.
00:26:46.00 So, to really understand how species evolve,
00:26:47.25 we need to study a lot of them.
00:26:50.17 Okay.
00:26:52.20 So, what are the main, main messages of that talk?
00:26:55.03 I think I said, already, everything, but just to sum up…
00:26:58.04 first, we have shown here that bat color vision
00:27:00.18 is adapted to diet and other conditions,
00:27:02.13 and it’s way more complex than we think it is,
00:27:05.07 and that we really need to study all the bats
00:27:07.20 to really have the big picture.
00:27:09.28 We have also seen that, by studying a lot of different species
00:27:12.19 and these kinds of traits, we can catch, really, evolution in action.
00:27:16.06 We can see what’s going on.
00:27:19.00 Species have evolved but are still evolving.
00:27:20.27 And especially in this world that is changing
00:27:22.22 with climate change and everything,
00:27:24.25 it’s really important to understand how species evolve
00:27:27.05 to protect them and to be able to understand what will be going on.
00:27:30.20 And finally, it’s really important to study biodiversity as a whole
00:27:34.29 because it can help us to reveal general concepts about evolution
00:27:39.03 and to really understand how species live in this world
00:27:42.16 and evolve, etc, etc.
00:27:45.16 For this study, I want to acknowledge a couple of people.
00:27:47.24 So, of course the people of the Sears lab I’m in:
00:27:50.02 my boss, Karen Sears, and all the people that participated in this work.
00:27:53.21 I want to also thank the main collaborators,
00:27:56.08 because this work has been done in collaboration
00:27:58.28 with many people in an NSF grant,
00:28:01.26 and so I want to acknowledge
00:28:04.20 the main collaborator on that project.
00:28:06.08 And also, I really want to acknowledge
00:28:09.08 all the people in iBiology
00:28:11.15 and my coaches to help us to shape this talk.
00:28:14.11 And thank you all for your attention.

This Talk

Speaker: Alexa Sadier

Audience:

General Public
Educators of H. School / Intro Undergrad
Student
Educators of Adv. Undergrad / Grad
Researcher
Educators

Recorded: November 2020

Talk Overview

Bat species are numerous and diverse, and are found in nearly every corner of the globe. Therefore, they serve as a valuable system to study the evolution of mammalian traits. Dr. Alexa Sadier collected field and museum samples from over 50 species of bats to ask how color vision evolved in this unique group of mammals. By looking at gene expression at multiple levels – DNA, RNA, and protein – Sadier determined that different bat species have color vision capabilities adapted to their diets, and UV vision has been lost independently in multiple species through regulation of all levels of gene expression. By “catching” evolution in action, Sadier’s research has revealed important insights into the mechanisms of evolution through trait loss.

Speaker Bio

Alexa Sadier

Alexa Sadier

Alexa Sadier received her PhD in Evolutionary and Developmental Biology at the Institute of Functional Genomics in Lyon, France. She performed postdoctoral research with Karen Sears at UCLA. Sadier’s research focuses on the genomic, developmental, and ecological basis of the evolutionary diversification of sensory systems and teeth in bats. alexasadier.com Continue Reading

Credits

Eric Kornblum (iBiology): Videographer, editor
Brittany Anderton (iBiology): Producer
Chris George (iBiology): Graphics
Maggie Hubbard (iBiology): Graphics

Comments

Amal says

October 28, 2021 at 2:23 am

I really enjoyed the research snippet. That, ladies and gentlemen, is how science can be rendered nothing short of 𝗗𝗔𝗭𝗭𝗟𝗜𝗡𝗚𝗟𝗬 𝗕𝗥𝗜𝗟𝗟𝗜𝗔𝗡𝗧. Nicely done!

Reply
Fei says

January 24, 2022 at 12:58 pm

Really enjoy this interesting talk! I have one question about the diversity within species, if the evolution is an ongoing process and if there is no significant selection pressure on this trait, does it mean there should be diversity in each species?

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