From Supercontinents to Islands – Evolution in Motion

Well, it’s my great pleasure
to introduce my friend and colleague, Gonzalo Giribet,
who is the Alexander Agassiz Professor and curator
of invertebrate zoology here at the Museum of
Comparative Zoology. By now, Gonzalo is
familiar to many of you who frequent these talks. This is actually his third
Natural History Museum talk. And so I’ll keep my
introductory remarks short. Now, I could give the
standard introduction, going over his academic
and life details– born in Spain, undergraduate and
graduate degrees in Barcelona, a post-doc at the
American Museum of Natural History in New York
before arriving here at Harvard in the year 2000. I could list the
extraordinarily long list of papers he has published,
many of them very influential, and many in the very top
journals in the field. I could mention the incredibly
long list of big money grants he’s received,
including one very recently, or the long list of honors,
most recently a Guggenheim Fellowship to finish a book. But that does not really capture
who Gonzalo is or what he does. To do that, I think you need to
appreciate that, even as he has been at the very forefront
of using molecular, and now genomic, techniques
to understand invertebrate evolution, even
as he has been pioneering these approaches in the lab,
he has, at the same time, had an extraordinary program
of research in the field. In just the last
five years alone, he has conducted field studies
in Australia, New Zealand, Brazil, Spain, Portugal, South
Africa, Mexico, Panama, Belize, the Amazon, and most
recently, Antarctica. And I suspect that
we’ll hear today that I’ve managed to miss a
few of them along the way. And what is it that he’s
doing on these expeditions? What is he studying? Well, he’s studying, basically,
everything, or at least everything without a
backbone– from spiders to mollusks to worms and
everything in between. Gonzalo studies them all. In fact, I think
it’s no exaggeration to say that, at
this point, Gonzalo is the world’s leading authority
on invertebrate biodiversity. Now finally, on top
of all this, Gonzalo is a world-class
windsurfer, regularly competing in tournaments
in far-flung destinations around the world. Now, as you know, our
series this spring has focused on
evolution on islands. If there’s any theme that runs
through Gonzalo’s research, it is the importance of the
Earth’s deep time geological history in explaining patterns
of biological diversity. Tonight, Gonzalo will
show how this perspective of continental drift
and Earth history enlightens our understanding
of island evolution. So please join me in
welcoming Gonzalo Giribet, who will speak on From
Supercontinents to Islands, Evolution in Motion. Well, that’s quite
the introduction by the master of islands. And it’s going to be hard,
now, to stay on top of my talk. But it’s a great pleasure
to be here again, talking about some of the
research that not only me, but a lot of the
people in my lab, do. A lot of the results, a lot
of the research that I’m able to do– it’s because we
have a big team, a great team of people, all of whom work,
as Jonathan said, from genomics to going in the field and
collecting the very animals that we need for our research. I think that one of the things
that really characterizes our research program or
the program in my lab, is that we really need to
go and identify and describe the biodiversity that we use
for the research that we do. Today I’m going to focus on
one aspect of the research in the lab which is
related to islands. Now, you’ve heard
a lot of things about islands in this series. And many of those things,
like the odd animals that live in islands, these
flightless, giant birds and insects that
don’t fly anymore– we’ll see the ground foraging
bats that behave like a mouse, for example, or sunflower
plants that become trees instead of being like small,
woody plants, small plants there. We’ll see these hawks
that Darwin referred to in his books, that they were so
tame that he could knock them down off their perch
with the butt of his gun. Or we’ll see things like
the giant shrews that lived in the Mediterranean
or the dwarf elephants that lived in many places, in many
small islands from the islands off the coast of California
to a lot of the Mediterranean islands. So you’ve seen some
of these themes. And these themes are relevant
to all types of islands, no matter what origin they had. Another theme that
we see in islands is a theme of extinction. And this has to do, for
example– New Zealand, one of the islands
or the island systems we’re going to talk
about today– that it has very unique faunas. And from those
faunas that it has– the only mammals that really
lived in New Zealand are bats. But those bats became adapted to
have a very different behavior from the bats in other
places because there were no, for example,
mice or things like that. So many of them are foraging. They’re just in the ground. But of course, as
soon as men got there, so many of these
species, or at least the largest one of these
species, became extinct. The picture on the lower
left, that you can see there, is the last photo of one of the
members of this species that went extinct in 1967. The theme of extinction
is very common in islands. And it has to do
with the structure of the biology of the
organisms that live there, that they adapt to very
specific conditions, many times without predators. And as soon as there’s an
invasion, man-mediated or not, things just change very rapidly. You’ve seen, probably, in many
of the early talks, themes related to oceanic islands,
those islands that emerged de novo from the
middle of the ocean, whether it’s from a
plume in a volcano or whether they’re formed
in the coral reef areas. And these islands have a
series of conditions that make their biota to be what it is. For example, when they emerge
de novo from the ocean, they’re bare. They don’t have any
organisms living there. So one of the first
things that we see in these types of islands
is that the animals and plants that make it there,
they’re organisms that have the capacity to
disperse to these islands. So dispersal plays a
very important role in shaping up the
biodiversity of those islands. And that’s why it’s
not uncommon to find things that disperse very well. And then once they
get to those islands, they might radiate
and give origin to some of the biodiversity
that we find there. So dispersal plays a key role
in short ecological times. But then, once the
things arrive there, since there’s a lot of empty
niches, many of the groups that are not very diverse
in the centers of origin, they might diversify
in these islands and give rise to these
evolutionary radiations that are so famous in many
of those islands. So one of the patterns that
we find in these islands is that some of
the organisms that can fly– for example, birds
and a lot of seeds that disperse very well
through water– make it to all those islands. And then the things that
don’t disperse very well, they might be able to make
it to closer islands. And you have things in between. And some of these
graphs show you that some animals that don’t
disperse very well, if they attach to birds or seeds or some
other forms of vegetation that can actually float,
they will also make it to far, distant islands. And so depending on the
properties of those organisms, they are going to make it
to those islands or not. So the first things that
arrive to many oceanic islands are going to be birds, are
going to be flying insects, are going to be ballooning
spiders, and things like that. And this has been tested in
many groups of organisms. This is a spider of
the genus Tetragnatha. And a researcher who gave
one of the lectures here, Rosie Gillespie, has shown
that, as you go farther away from the source of
origin of these things, the more distant
islands start having more endemicity,
more species that only live in those islands. So Hawaii is one of the
most remote archipelagos in the world, and pretty
much, all the spiders of the genus Tetragnatha that
live in Hawaii are endemic. They only occur
in those islands. And if those are closer
to other sources, then you might have a
lower level of endemicity. So the common pattern that we
see there, for example, also in Hawaii, is that one
ancestor of the radiation of honeycreepers made it there. And then once they
get to the islands, they start diversifying. The habitats become
heterogeneous. They adapt to specific foods. And you end up having these
beautiful radiations that we’ve heard about all the time. And for example, also
another radiation, is what Jonathan Losos has been
working on in the Caribbean Anolis– how they’ve diversified
in those islands, how you have the same ecotypes that
evolve in different islands once these animals make it
into those bare habitats. The types of islands that
I’m going to talk about today are quite different. We call them continental
islands or fragment islands. These are islands that
originate by one big landmass fragmenting and giving
origin to a smaller landmass. We’ve talked about New
Zealand, for example. We’ll see some other ones. And these islands have very
different characteristics. When they form,
they are not bare. They’re carrying a lot
of the biodiversity that was originally in the continent
from where they fragmented. And they undergo several
processes, some of which are related to
the other islands. For example, there’s a
process called relaxation– that not all the
lineages that made into that original fragment
are going to make it through evolutionary history. Some of them go extinct. And others, because they
have, then, more availability of habitat, might also radiate. So we might have other types
of radiation, for example. One of the phenomena that
we’re going to talk about is the formation of what
is called paleoendemics. There are endemic organisms
that live in those islands. Those are relicts, often, or
we refer to them as relicts. They’re old lineages that were
inherited by those islands. Sometimes they disappear
everywhere else in the world. And they make it
a single species or very poor diverse groups that
only survive in those islands. And we’ll talk, also,
about some of the other– let me see– since
these islands are much older in
origin, in general, than the islands
that are formed de novo in the middle
of the ocean, we might have lineages that
are also very old in time. So what are some of the
major continental islands? Well, if we go to one
part of the world, if we center here in Southeast
Asia, we see a lot of islands. And in fact, in
this map, we can see most of the major continental
islands in the world. We have Madagascar here,
off the coast of Africa. We have Sri Lanka
here, south of India. We have many of the islands of
Southeast Asia, like Sumatra, Java, Borneo, Sulawesi. But not all the islands
in Southeast Asia are of continental origin. For example, most
of the Philippines are islands that are
formed de novo, most from volcanic origin, some
of them from coral origin. There are some Philippine
islands–like Palawan that is actually continental. And it was once
connected to Borneo. And then we have
Papua New Guinea, which fragmented off Australia,
and some of the islands that we’ve done
most work in my lab, like New Caledonia, which
is here, and New Zealand. Poor New Zealand is
always off the map. It’s always really hard to get. So just to summarize the
difference between these types of islands– what we
call island fragments or the continental islands,
they originate by fragmentation of a landmass that existed. And this fragmentation,
as the island separates, takes the biodiversity
that live there, goes through some ecological
processes, like relaxation and formation of new species,
and continues its evolution. The difference with
the oceanic islands is they emerge from nothing. Once you have those
islands, they’re empty. And they start receiving
organisms by immigration. And then the process is
the first arrivers normally are the ones who might
be able to make it and to diversify– not always,
but that’s generally the case. So I want to talk about
a few processes that are related to some of these
continental islands today. One is continental breakup. This is a process
that is very important to understand the
biodiversity of these islands. The other things
that we’re going to talk about a little bit is
paleoendemics and this concept of relictualization,
relict taxa that have survived in
some of these places, and perhaps a little bit of a
higher-level enedemism, things that are– like in
oceanic islands, normally, since they
are relatively new, you might find that,
suddenly, the honeycreepers have many species or the
anoles have many species. But those are still
the same genera that you find in the areas
where they originated. While in these oceanic
island, since they are very old, in
general, what you have is not new species
within a group, but you might have genera
or families or orders. So this is what I refer to
with very old lineages that have persisted there. This is one view of
the world, nowadays. And the world is formed
by these tectonic plates. And those tectonic
plates are very dynamic. This thing is
moving all the time. Some of them are very stable. It’s very unlikely
that you’re going to have an earthquake in the
middle of the Eurasian plate. But it’s very likely
that, if you are along this area where these two
plates are creating friction, you’re going to have lots of
volcanoes, lots of earthquakes, tsunamis, and these things. And this is very well known. In fact, that the
area of the Pacific is called a ring of
fire because there is a lot of seismic
activity going on there. And this is telling
you something about the dynamic
nature of the planet. The continents are very old. So we have continents
that have rocks that are 4.4 billion years old. Some of these areas have been
maintained for a long time. And the collision of these
plates create things. For example, when
the Indian plate collided against the Eurasian
plate, it went very fast, collided with a lot
of energy, and formed the highest mountain range
that we know of nowadays, the Himalayas, for example. When we look at the ocean floor,
the story is very different. The ocean is very young. So what this graph is
telling you is, for example, here, there is an area where you
have new sea floor being formed in the middle of the Atlantic. And this is actually
where you will find a lot of the
oceanic islands that emerged de novo–
and the same thing if you go to the Pacific plate. Red means very young. And as you get
away from the area where the sea floor
is forming, the ocean is getting older and older. But you see that the ages
of the Atlantic, when you look at these
scales, they are in the order of
100 million years. I know 100 million
years a lot of time, but compared to the
4.4 billion that we have in some terrestrial rocks,
it’s actually very young. And in fact, there’s
very little sea floor that is older than
100 million years. And there’s a little bit here
in the Tethys that gets down to 260, 280 million years. But most of the sea
floor is very young, which means that what’s
happening all the time is that, as these
continents reconfigure, there’s new sea floor
that is being formed. And when it collides with the
continent, since it’s denser, it goes underneath. And it gets absorbed
by the crust. And that cycle goes
on all the time. What that cycle is doing
is that the continents don’t look like they do nowadays
through their entire history. So if we go back in
time, to this area around the Paleozoic–
so you have that most of the
southern continents form this large landmass
that is called Gondwana. And as you go about
120 million years, Gondwana started
splitting, first with opening of
the Atlantic Ocean, and then it kept separating. Here you have about
99 million years ago until 67 million years
ago when the continents are beginning to look
a little bit more like we know them nowadays. So what I’m trying to do is
to study the biota, mostly the invertebrates that
live in these landmasses, and see how they’ve
been reconfiguring as these continents move apart. And we’re especially
studying a lot of the taxa that live, a lot
of the invertebrates that live, in some of the island
fragments that were left after the break up of Gondwana. And the break up was very
important in many ways. We can see here, for example,
the Indian subcontinent breaks up from the
north part of Antarctica and starts going
north very quickly. It leaves Madagascar behind
and then keeps going north until it collided with
Southeast Asia, for example. And if we look from
another perspective, one that has interested me
a lot, is the connection of the southern continents. We see here the world
look from Antarctica. When we go about 50
million years ago, there was still a connection
between South America, Antarctica, and Australia. Antarctica was in
the South Pole, but it wasn’t as
cold as it is today. So there were a lot
of animals and plants that lived over there. In fact, Antarctica is that cold
not because it’s in the South Pole, which, in part, it is. But it is because,
after a certain time, these connections broke–
this one and this one, here– the Drake
Passage opened up and created the
circum-Antarctic current that has been isolating,
thermically, Antarctica from the rest of the oceans. There’s very little
water mixing, and it’s been creating,
basically, a freezer. It’s isolating it from
the rest of the world. And that’s when Antarctica
became completely frozen, and a lot of the biodiversity
from there disappeared. So many of the
animals that I study, they live in what I call
circum-Antarctic Gondwana. So the landmasses that were
once touching Gondwana– this is South America, this
is South Africa, Madagascar, India has gone north,
Australia, and New Zealand. And these things were
connected to Antarctica. And many of the organisms
that we study nowadays did live in Antarctica. We just don’t find them
alive there anymore. And we cannot find the fossils
because the fossils are under, sometimes, kilometers of ice. So it’s very difficult to get
to the rocks in Antarctica to look for some
of these things. And one of the
things that we try to do when we find a
distribution of organisms that live around Antarctica,
we tend to say, well, these organisms’
today are found in this temperate Gondwana. Therefore, they
originated there. And they’ve been breaking
up with the continents. And they haven’t moved around. And we used to explain that
these distributions are telling us something about
the history of these groups. Now, this is not
technically correct. And we can draw a
cladogram– the relationships of these organisms that
live in these landmasses. And we can use techniques
like looking at morphology or looking at
molecules and generate these schemes, these things. We call them phylogenetic trees. And they’re telling us that,
for example, the animal A and B have a common ancestor. They were related. And we can say, well, A lives
in Chile or South America. B lives in South Africa. And then we can translate
that taxon cladogram into what we call
the area cladogram. And it’s telling us
that, for that organism, there’s been a connection
between South Africa and South America, for example. And normally, when we see those
distributions, we say, huh. This is because these things
had a Gondwanan distribution, originally. They’ve been breaking
apart with the continents. And that’s where we find those. But nowadays, that’s
not necessarily the case because we could also
explain the same distribution if these organisms
had originated here, and they had been
circulating around with the
circum-antarctic current. And they’ve been
distributed along all that. So the fact that
we find organisms living in the former
Gondwanan continent doesn’t mean that they
have evolved there. So what we’re doing nowadays
to study biogeography is not only looking
at the distributions and the cladograms
of these organisms, but we need to apply some
type of fancy techniques to try to come up with the age
when those distributions were achieved. And once we have the
age, we can say, look, this distribution was acquired
before the continents broke. Therefore, that
distribution is the legacy of the continental breakup, for
example– as opposed to saying, look, this is too young. The diversification
of these things has occurred in the
last 10 million years when the continents were
already shaped like that. Therefore, we cannot say that
that is a distribution that was achieved by continental breakup. And these are the
models that we do. For example, we have a landmass
that was once continuous. And we’re going to call the
red part of the landmass and the blue part
of the landmass. And that landmass breaks up
into two, and it separates. Now there’s sea in between. And those two landmasses
keep separating. And we might find three types of
distributions that are actually congruent with those
landmasses, but depending on the timing of
those distributions, the evolutionary
history of those groups is completely different. For example, here, the
group originates when the two landmasses separate. And then, they diversify, each
one on of those landmasses. And we call that thing
vicariance biogeography, for example. We may have examples where
the origin of the groups is prior to the breakup. The group starts forming. And then they get carried over
by each one of those landmasses and continue to diversify. And for us, it’s very difficult
to distinguish these two scenarios unless there’s
a very long history before the breakup. But we might find another
distribution which is perfectly the same or equivalent
to that one, except that the group has
originated after the two landmasses separate. And therefore, we cannot say
that that distribution that matches that Gondwana and
biogeographic scenario, is actually the consequence
of the continental breakup. The only explanation
that we can give here is that the group originated
after the continents broke. And the current distribution
has been achieved a posteriori by dispersal, for example. So that’s what
we’re trying to do. And I’ll bring that back to
our research in a little bit. While we’re talking about some
other things, often islands, we’re talking about
paleoendemics and relict taxa. And some of those are
very prominent in a lot of the discussions
on biogeography. This is Amborella. Amborella is a
very weird flower. It’s a flower that lives
only in New Caledonia. And New Caledonia
is this tiny island, which is part of a larger
continent called Zealandia. Why is Amborella
relevant at all? A little flower, not really
pretty, or not very pretty– well, it’s very
interesting because there’s one species of Amborella. And it’s the sister group to
all other flowering plants. This means that the first
flowering plant, when it diversified, gave origin to
one lineage, which is Amborella nowadays, or survived
only by Amborella, and another lineage
that gave origin to all of the other flowering
plants that you know. So from the perspective of
an evolutionary biologist, this is a very important
flower because it is the closest group that
you have to the earliest divergence of the flower. So islands often retain
some of these groups. Now, can we say–
and people sometimes have said– oh, flowering plants
originated in New Caledonia because the most basal flowering
plant or the first offshoot of the flowering plants
lives in New Caledonia. Well, unfortunately,
we cannot say that. And I’m going to show you
that with another example in a second. So Amborella is a
paleoendemic, a relict, a very depauperate old lineage
with primitive morphology for flowering plants. And we find paleoendemics that
are common in many islands. For example, when we
go to New Zealand, on one of my
favorite islands, we have the moas, which
are these giant ratites, flightless birds,
and the kiwi birds. We’ll talk about
the tuatara today– this weird reptile that
looks like a lizard, but it’s not a lizard– and some
frogs that are very old, also. And I’ll talk
later on about some of my velvet worms
and harvestmen. Here is the tuatara. I assume many of you know a
lot about natural history, and you have heard
about this little thing, which we cannot call a lizard. Tuataras are very interesting. Again, there’s one species. And they’re like Amborella. They’re the sister
group to all squamates. Here you have your geckos,
your lizards, your snakes, all those things. And then there’s
this other lineage from the early divergence
of these things, which are the tuataras, which
today– again, like Amborella only lives in New Caledonia–
the tuatara only live ins New Zealand. And we could say the same thing. Did squamates or the
ancestor of squamates originate in New Zealand? No. We know that’s not true. And we know that because,
unlike Amborella, we have a good fossil record
of a clade of reptiles that is called Rhynchocephalians. And Rhynchocephalians were
distributed all over the world, with lots of fossils in
North America and Europe. This is a bias, not because
they lived here, probably more, but because there’s many
more paleontologists that have worked in those places. But they had a
worldwide distribution. And what’s happened
with Rhynchocephalians is that they have gone
extinct everywhere. And because New Zealand
got isolated at one point and didn’t have many
predators, and for the chances of evolution– that we know that
they don’t play by the rules– they just went from
a global distribution to just one species living
nowadays in New Zealand. And we don’t know
for how long it’s going live there
because it’s been decimated from the mainland. It’s now only living
in some sanctuaries and in a few islands offshore
that are deprived of rats. So this paleoendemic
is a very old lineage with very low diversity
that has gone extinct in the rest of the world and
has survived in an island. So that’s why islands,
these continental islands, tend to be very interesting
because they might maintain some of these paleoendemics. But they’re not informing
us a lot about the origin of the island, about how
those groups diversify because we only have one. We can tell that it separated
from the rest of the squamates about 280 million years ago. But we don’t know
anything that has been going on during these 280
million years of evolution. We cannot do any molecular
estimates because there’s no more diversity there. So there’s very
little information that we get from Amborella
or from the tuatara to understand the biological
history of those islands. So they’re very charismatic. We always talk about them
when we work on these islands. But there’s very little
things that we can do. And this is why I work on
other types of animals. I work on things, first,
that you can collect many, that you can bring into the lab,
and you can sequence their DNA, that they are diverse in
those islands, the groups that have diversified in not
only one of those islands, but in many of them. And they’re found in all
the Gondwanan landmasses, for example. And some of these places have
had very troubled history. This is difficult, sometimes, to
understand some of these maps. Here is East Antarctica
and Australia. And you have a lot of
stuff going on here. And this stuff,
it’s microplates. And some of those microplates
have something here, which will give rise to an
island like New Caledonia, and some other parts
here that are actually three main islands
that, at one point, will merge and form New Zealand. So we have these organisms that
lived in all these landmasses, that were connected
to larger landmasses, and that, through history,
they have changed. For example, the
history of New Zealand is very interesting for me
because you can actually test many hypotheses
of island evolution, from very old ones
to very recent ones. New Zealand has had a
very troubled history that can be summarized that
about 80 million years ago, it separated from Australia by
the opening of the Tasman Sea. And then it kept
drifting apart and then, about 25 million years ago,
went through an episode. It was a global
episode that affected New Zealand like many
other places, which is called the Oligocene drowning. Most of New Zealand
went below sea water. There’s a controversy
whether the whole New Zealand went under sea water. And that’s one of
the things that I’ve been studying through
the years, trying to understand whether New
Zealand really went underwater at 25 million years ago or not. But whether it went all
the way down or not, this is the surface
of New Zealand. This will be mother New Zealand,
whatever area unit we use. But you can see that,
during the Oligocene, there was only a little fraction
of the total surface of New Zealand above sea water. In addition to that, about
7 million years ago, it started with the
orogeny of the Southern Alps, the formation
of the Southern Alps, that are beautiful, one of
the most beautiful mountain ranges in the world. And it formed along this
west coast of New Zealand, isolating the east
and the west part and giving them very
different climate. The west part is really
wet, and the east part has become much drier. Also about 2 million
years ago, there was the glaciations
that were also global that affected New
Zealand to a big degree. And then, even only 16,000
years ago– this is, we’re talking now about human
times– the north island and the south island of New
Zealand separated by a very drastic fault movement. New Zealand is in
between two plates. And there was one
slippage of those plates, and only 16,000 years ago, they
separated, those two islands. This is a schematic of New
Zealand through all these 80 million years. But they never really looked
like that until very recently. This is actually what
New Zealand looked like, these very different plates. And probably each one
of them originated from a different
part of Australia and carry on their own lineages. And we still see
some of the history of those lineages in some
of the groups that we use. And they had very little
dispersal ability. So New Zealand has
changed in shape, even is changing vegetation coverage. This is during the Pleistocene. About 1.8 million years ago, New
Zealand was a very large forest and then underwent
a much drier period. So you have there
many different levels of hypotheses that we can test
now with these methods that allow us to give time estimates
to the biological events that have happened through the
history of the groups. So that’s what we’re
doing nowadays. And one of them that we’re
testing, specifically, is this idea. We’ve seen that New Zealand,
about 25 million years ago, lost a lot of its
surface going underwater. But a few years ago– about 10
years ago or nine years ago– there was a new wave of
biologists from New Zealand. We’re were still
debating whether they did that to get more
grant money or not. But they just said that
New Zealand was completely submerged and that all the
biota that we find nowadays in New Zealand, including the
tuatara that has been extinct everywhere else and
many other things– they just arrived to New Zealand
in the last 20 to 25 million years, which seems
a very short time for some of the groups that
we have nowadays. At the time with my former
student, graduate student Sarah Boyer, who’s now a professor
at Macalester College, we wrote a reply
saying that, look, we have many candidate
organisms that would contradict that hypothesis. But to tell you the
truth, at that time, we hadn’t done any
of these exercises of collecting lots of animals
and providing dated phylogenies where we could actually test
these things, specifically. Because remember,
the difference is going to be not on the
distributions of the organisms. It’s going to be whether
those organisms were there before 25 million years
ago or were not there at 25 million years ago. So that’s the big difference. They are saying that
everything arrives from Australia or
from nearby landmasses after 25 million years ago. So that’s what we want to test. And what organisms do we use
to test some of these things. Well, we’re looking
for very old lineages. So one of the good things
of working on invertebrates is that we have animals
that are very old. For example, this is the oldest
daddy long legs, a harvestman, that actually looks– well,
here it’s flat in a rock, so it doesn’t look like much. But what you see here
is the ovipositor of the female that has exactly
the same structure that we have in modern daddy
long legs that you find running across the yard. And this animal has a lot of
the characteristics that are very similar to modern ones. This is a fossil
from the Rhynie Chert that is more than 400
million years old, the daddy long legs looking
quite similar to what we have nowadays. They were, even if it’s
flat in a rock, already around 400 million years ago. If you are skeptical
with flat rocks, which I understand that
some people might be, we can go 300 million years ago. And then we have
three-dimensional daddy long legs. What we have here is a rock. It’s a nodule off a rock. And when we scan it with
certain machines that we use, the micro CT scanners, we
see what’s inside that rock. And there’s a
differential scanning that picks up different
densities in the rock. And then we can reconstruct
that with a computer. And we have a perfectly defined
three-dimensional animal that we can rotate and look
at all the characteristics. We can see the chelicers. We can see the palp. We can see the legs. We can count the tarsum he
has on the legs on an animal that you’re not
seeing physically. It’s inside a rock, but
it’s three-dimensional. And we don’t only have one. We have many. We can look at structures
like the genitalia of this 300 million-year-old. And we have many other
ones, some of which look very much like some of
the daddy long legs, again, that we find out here
running in our backyards. So this is telling us that
these organisms are very old. But they haven’t evolved much. And we know from other
studies that they’ve been in the same
areas for a long time. We also look at another group of
organisms called velvet worms. And this is a paper
we have now submitted describing the first unambiguous
terrestrial velvet worm. This is from the same
sediments that we had the three-dimensional ones. Unfortunately, this is
not three dimensional. But when we look at the
structure of these things– the angulation of the cuticle,
the little antenna that it has here– it looks
exactly like the ones from these modern velvet worms. That antenna with these annuli
that alternate large and thin ones, is very similar to these
antenna that we find here. These animals lived in
terrestrial habitats. They are the ancestors of
these daddy long legs, some of the most beautiful animals
that you can encounter, if you go around. And these velvet worms have a
very interesting distribution. This is the
distribution in green of a family called
peripathidae that is being studied by one of the
graduate students in my lab. And then blue, you have
this other distribution of the other family
called peripatopsidae, which is very similar to some
of the other distributions that I’ve shown you
earlier, these animals that lived in circum-antarctic
Gondwana, or what I call the
temperate Gondwana. So we’re going focus a
little bit on those ones. And a couple years ago,
we published a study where we’re reconstructing
the relationships among these organisms
and also dating the trees to see if we can test
some of these hypotheses about vicariance biogeography,
about whether New Zealand had had diversity surviving this
supposed drowning effect. And we’re looking at very
ancient groups, again, more than 300 million years old. And we have collected it along a
lot of the distribution places. And we can look at the general
tree of the velvet worms. And what we found
is that this family, the circum-antarctic
Gondwanan family, has a clade, or two clades, two
groups that have a trans Tasman Sea distribution, meaning
that they are in New Zealand and in Tasmania and Australia. The opening of the
Tasman Sea is that event that I told you earlier–
about 80 million years ago when New Zealand separated. And we can follow many
of the major splits of each one of these groups, the
separation of the two families is about 350 million years
ago, the diversification of these peripatopsids,
which follow very well the splitting of eastern
Gondwana from western Gondwana, and then the split
of eastern Gondwana into the different landmasses. And if we look into New
Zealand more specifically, we find one clade
of a genus called Peripatus that is found both
in New Zealand and in Tasmania. And this is at the time–
the diversification around 80 million years,
which is when the Tasman Sea was beginning to open. And then, another
group– so it’s a repeated experiment
of nature when we have another
group of velvet worms also between New
Zealand and Tasmania. And these two have, actually,
very different biologies. One of them gives
birth to little babies that they have in a uterus. And the other one lays eggs. So there’s no way that this
could be the same lineage that we don’t have resolution. These are two old lineages
with different morphologies. So what we do with
these types of organisms is to study precisely this
thing, the continental drift. Actually, we’ve been working on
these things for a long time. A few years ago Carl
Zimmer published an article in the New York Times
describing some of our research. And this was about the
hitchhikers of the plates. This is something
that someone sent me from the Metro News in
Dublin using our photos. This is one of my photos. I don’t know where
they got it from. They didn’t ask for it. But anyhow, it’s nice to see
your research highlighted in some of the popular press. And they were talking
about these animals because this group
of daddy long legs has a distribution that looks
very much what we have here. We have a family that lives in
the older Laurasian continent, the northern continent. And we have other
families that live in the southern continents,
one of which is distributed across Africa and
tropical South America, and then this other one that
leaves in circum-antarctic Gondwana, South America,
southern Africa, Madagascar, the Indian subcontinent– but
only in Sri Lanka, and then Australia and New Zealand. And these are beautiful examples
to do some of these studies. Our big conundrum here
is this family, which is endemic to New Caledonia. And it’s not related to any of
the families that are closest, geographically. So this is one of the big
things that we haven’t been able to disentangle. New Caledonia has a
similar controversy to the one in New
Zealand, except that it was below sea water until
37 million years ago. And the geological evidence
for that is very strong. So we have a lineage
that is endemic to New Caledonia, another Amborella,
except that this one has many species. Now, we cannot say that those
species diversified before 37 million years ago. Our molecular dating
puts the diversification around 35 million. With the error bars we cannot
really distinguish that hypothesis. So there is the possibility that
this thing had arrived there after New Caledonia reemerged. When we go back in time looking
at some of these distributions, obviously we postulated
they’ve been acquired through continental drift. So let’s go back in time
a few million years ago. So if we go to the
period of the Cretaceous where Earth, more or
less, looked like that, you can see that
the group that is found in West Africa and
tropical South America was a contiguous group. So it diversified like that. And these groups
that were actually in the southern continents
around Antarctica, they’re getting
closer and closer. Those groups had a
continuous distribution before they started
diversifying. Another of my grad students
focuses on this other problem, which is Southeast Asia, which
is really, really complicated. It’s one of the most
complicated geological systems in the world, with so many
islands that have come together and have come apart. And today we’re not going to
have time to talk about them. But for island biogeography,
this another of the areas that is most interesting. And if we continue
going back in time, you can see that these
continents at one point, became together. And Southeast Asia was not part
of Laurasia, the large content that is most of Asia. Actually, Southeast Asia
came from the northern ring of Gondwana. But it split up very early. So what we find is
that these things, when we go through time, end up
related to some of those Gondwanan lineages. And with this, we go
to all these places. This is when I have to travel
as much as Jonathan said. And we need to go
to all these places to collect these animals
because very few people can collect these tiny, little
things from the leaf litter. And we need to go
there and collect them to have these densely
sampled studies when we can represent all the landmasses. And this is, for example,
the one from New Caledonia that I’m telling you. These all diversified
very recently despite having a
very long branch. So we could have only one. It will be Amborella. But at least,
since we have more, we can start testing
some of these hypotheses about their diversification. So the one that we’ve centered
most of our attention, until now, in the
lab is the group that lives around Antarctica. And I always say, I
will bet anything I have that there were
Cyphophthalmi living in the middle of Antarctica. We’re just never
going to find it. And these are beautiful animals
for those of you who like them. For the rest of
the people, they’re just tiny, little, brown,
indistinct daddy long legs. But I love them. I love them because they
have all that history written into them. And we’ve been constructing
these phylogenetic analyses with these groups of organisms. And we’re able to test once
we have a dense sampling. This study is 16 years
of sampling these things in all these landmasses. And we finally got it
published this month, actually. And one of the things
that we show here is that, from the three genera
that we find in New Zealand, one is a little
bit like Amborella. It has one species, maybe two. There’s not much we can say. It’s an old lineage
that relates to some, perhaps, Australian groups. But there’s not much we can say. But for the other two lineages
that live in New Zealand– one is this genus Aoraki that
we named after Mount Cook. Aoraki is the Maorian
name of Mount Cook. And we can see two
things in this tree. One is that the groups
starts diversifying around the Triassic Jurassic. This is way before
the 25 million years of the purported submersion. And also, when we do some
analysis of the diversification of this group, we
see that the group has been diversified
at a constant rate through time, meaning
that they haven’t had weird things in the
diversification rates that you would expect by most
of the landmass of New Zealand disappearing. When we look at the other genus,
which is even more diverse, Rakaia, it originates
a little bit earlier. And we have large error
bars, but the error bar never even gets close to
the 25 million years. So we’re talking
about groups that have been diversifying at a
constant rate for about 150 million years in New Zealand. This is telling me
that these groups have ancient clades of
genesis in New Zealand, even when it was
connected to Australia, and that they’ve been
continuing their evolution in their landmasses
for a long time. So we can test these hypotheses. And once we have more and
more organisms– that’s why we’re studying
the velvet worms and other groups of
daddy long legs– but then we can say, look, it
seems that all of these groups are contradicting,
are falsifying, the hypothesis that New Zealand
was completely underwater. So that’s the type of
research that we do. Now, continental
islands are complicated. For example, New Zealand–
we do have groups that have dispersed there. If this is the Oligocene
drowning episode, we have molecular signals
from many groups telling us that the group has
originated in New Zealand at a very
recent time and has diversified at a recent time. So the fact that we have
groups that have arrived there by dispersal very
recently does not contradict that the island
was or was not submerged. We have other groups that
might have originated before this Oligocene event,
but the diversification is more recent–
sort of what I was saying with the other
group from New Caledonia. This group doesn’t allow us to
falsify whether this island was submerged or not
because it could have come from Australia,
one arrival here and then diversified. So again, that group doesn’t
falsify our hypotheses. We have groups that are
beginning to get closer, like kiwis and moas. We know they’ve
been diversifying for quite some time, but their
diversification did not, again, pass this event. And many of the groups
that we’re looking for are groups that are much older,
that they’ve been diversifying through this
episode of drowning, so we can use those to falsify
the idea or the hypothesis that the islands have
been completely submerged. I was mentioning
earlier that there are systems that are
even more complex, where you have
not only– I mean, New Zealand is still isolated,
but in Southeast Asia you have so many islands,
some of continental origin, some of volcanic origin,
some of them, like Sulawesi, is composed of
different terrains and different
volcanic accretions. So it’s really difficult to
disentangle what’s going on. And then, also, the sea
level of these things have changed quite a lot in
the last few million years. So what looks like
many islands nowadays, when they sea level was lower,
was a contiguous landmass that was connected
to Southeast Asia. So there was a lot of influence
of Southeast Asian taxa. So really, working in
Southeast Asia– it’s very difficult to be able to
find good examples to test some of these hypotheses. But one of my grad
students from class did work there and
sample these things. We included samples from
all of the continents. We actually have a very
beautiful, similar story of these animals coming
from, as I said earlier, from the north part of
Antarctica or Gondwana, and then once it docked
with Southeast Asia, starts some level
of diversification. And we can see that this
diversification went in one direction until it
found the Himalayas and then into other directions,
radiating and giving origin to some of these diversity of
daddy long legs over there. We can’t really talk about that. I just want to finish
with some pretty pictures because I think that– and
I keep working in groups that were around Antarctica. I’ve been saying for
a long time that I would love to see what’s
in Antarctica, in terms of these groups. And I’ve said already that
I’m not going to see it. But at least, what I wanted
to do as I was recently in an Antarctic trip to look
for other groups and things that can actually help me
with some marine organisms to reconstruct some
of this biogeography. Now, marine organisms
are a little bit more complicated because they tend
to have dispersal larvae. But in Antarctica,
because of the climate, it has a lot of species
that are actually brothers. And species that
are brothers tend to have much more geographic
structure that perhaps we could use to study some of
these connections through time. So I don’t have many results,
but I have some pretty pictures of some other places where
we were just two months ago. We were actually
diving in these places, collecting some of
the animals, doing a lot of intertidal work,
which is quite challenging because you’re trying to get in
between these pieces of iceberg to sample your animals,
getting into the water to get our samples,
always making sure there’s no seals around,
no leopard seals around. And you know that Antarctica
is such a special place. It’s the only place where
you have fishes where their blood has no hemoglobin
because they can’t transport the oxygen. It will
freeze the hemoglobin, so they don’t have hemoglobin. Amazing landscapes–
and there are actually some paleontologists working
in some of these places, looking at the origins
of, for example, penguins. So there’s some vertebrae
paleontologists– and also dinosaurs. I’m more interested, again,
in some of the invertebrates. These are pycnogonids. It’s a group that is very
diverse in Antarctica. We collected lots of animals,
lots of these things– beautiful nudibranchs
or sea slugs. I thought trilobites
had gone extinct, but there’s these
isopods in Antarctica that look like trilobites. It’s amazing. And all the fauna
there is exceptional. I mean, this is one
ribbon worm, a Nemertea that I was having there. They get much larger
than this, actually. And with that, I just
want to thank everyone from the lab who has helped
a lot with all this research and to you for coming here
and listening to this talk. And if you have any questions,
I’ll be happy to try to answer.

2 thoughts on “From Supercontinents to Islands – Evolution in Motion”

  1. Thank you for the very beautifully informative presentation. I enjoy the approach Prof. Giribet took, it allowed me to quite easily follow his trail of thought along with the data which is very much a benefit when absorbing such a data-rich talk as this one.

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