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Are you ready to hear a story about sex that you're not
going to believe?
Humans have such a perception of reproduction
that's human-centric.
And when that's challenged, it really throws folks for a loop
to think of something that doesn't need its own males,
but crosses these species boundaries in order
to obtain that reproductive material.
What does a world look like with no males or clonal
reproduction?
What does that mean from the perspective
these cute little animals?
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ROB DENTON: My name is Rob Denton.
I'm an assistant professor at the University
of Minnesota Morris.
These salamanders are unbelievable.
They're an all-female group of salamanders
that can steal sperm from males of other species.
KATIE GREENWALD: My name is Katie Greenwald.
I am an associate professor at Eastern Michigan University
in Ypsilanti, Michigan.
If you think about it, a lineage that's all made up of females
can actually grow twice as fast as a lineage that
has both males and females.
Numbers-wise, that lineage should eventually
swamp out, outcompete and beat a lineage
that has evolved to have both males and females.
ROB DENTON: We sometimes call this the twofold cost of males.
It costs to make males.
And males take away resources that could be used for females.
It's still relatively mysterious why sex evolved
and how it's been maintained for so long
across so many different species,
across the tree of life.
KATIE GREENWALD: The reason that we're
so interested in these sexual asexual salamanders,
is that they are virtually able to sort
of flip-flop between sexual and asexual reproduction.
These various options in terms of how these offspring are
produced is as far as we know, completely globally unique.
And it makes the system a really excellent one
to look at when sexual reproduction is
adaptive versus when asexual reproduction is adaptive.
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ROB DENTON: Imagine you are one of these females.
You come to a wetland in the spring
and you proceed to find a packet of sperm
at that wetland that was laid there
by a male of a different species.
You require that sperm just to even have eggs,
to produce eggs and lay them.
You do so, and most of your offspring are clones of mom.
They're exactly the same.
They have all the same chromosomes, all
the same genetic material.
What makes these animals separate and distinct
and interesting, is the rate at which those other genomes
sneak into the offspring.
KATIE GREENWALD: A typical sexually
reproducing organisms are getting one set of their DNA,
set of chromosomes from mom, one set from dad.
And so all of us have two sets of chromosomes.
The unisexual salamanders, we do sometimes
get them with two sets.
But it's much more common for them
to have three or four sets.
And we sometimes even find them with five.
Five tends to be about where they max out.
Ohio and Indiana are kind of the epicenter of craziness
for the complex, because there are actually
five different sexual species that they can reproduce with,
that they can breed with the males,
and then potentially incorporate those males' DNA.
It's not only that they have these different potential
outcomes, but that even within a single clutch of eggs where
those are all siblings, all sisters,
you may have actually different types of salamanders
being produced.
ROB DENTON: It's amazing that they have this scenario having
multiple genomes.
But I think what puts it into perspective,
is how distantly related these species are that are sharing
this genetic information.
If we were to take a sample of my blood
and I had a set of chromosomes from my mother, from my father,
but in addition, a whole set from a gorilla,
from an orangutan, from a chimpanzee,
that's the type of evolutionary divergence
between these salamanders.
But I would be a fully functioning normal human being.
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SPEAKER 1: You have a salamander in here.
KATIE GREENWALD: No.
SPEAKER 1: Yes.
KATIE GREENWALD: What?
SPEAKER 1: Yes, yes.
KATIE GREENWALD: Oh, buddy.
One trap out of.
Are you kidding me?
What we're setting up here are breeding experiments
where we put the unisexual females in with different types
of males.
And then we genotype the parents and the offspring
to see when the male DNA makes it in.
So so far what we've been looking at,
is whether the female has any preference for a male that's
from her same pond versus a male that's
from a more distant pond.
And over the last couple of years,
we've been running these experiments
and are so far seeing a pattern where the females are
more likely to include the male's DNA
if he's from the same pond that she
is versus a pond on the other side of the reserve.
You could imagine, that if you are
a unisexual with a lot of blue spotted DNA
and you end up in a pond with a lot of Jefferson salamanders,
that's probably a good place to be a Jefferson salamander.
And so as that female, are you more likely then,
to add some of those Jefferson's genes to your offspring?
In which case, you're able to potentially grab
a whole locally adapted genome and stick it
right into your offspring without splitting it in half.
ROB DENTON: So I'm working to establish
a collection of these animals that
captures their whole diversity across their range,
from Kentucky to Maine to Minnesota to Canada.
Some of these people who work for state agencies or wildlife
management areas, sample these animals every year.
Help them cross the road, protect them,
educate the public about these animals,
without ever really knowing what they have.
How many genomes does it have?
And where do they come from?
And so this is a way that we can answer some of those questions.
And also ask more basic research questions
about their evolution, for instance.
This scenario of having these multiple genomes
produces some really confusing results.
So for example, we have studies that
show that they can regenerate their tissues faster
than sexual species.
At the same time, there are other tests,
such as locomotor endurance, where they perform really
poorly.
They're very successful.
Across their range, they're often abundant.
Sometimes they can outnumber the sexual species by 2 to 1,
3 to 1 at these wetlands.
So we know they're doing well.
We know they've been around for a really long time.
But it's really difficult to explain why that is.
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KATIE GREENWALD: These salamanders really
are taking advantage of the system.
They're all-female, so they don't bear
that cost of producing males.
But they're occasionally incorporating DNA
from other species.
In some ways, it seems like this potentially totally unique
evolutionary win-win, which might ultimately
let us learn a little bit more about the evolution
and maintenance of sexual reproduction.
ROB DENTON: They defy all boundaries
of what we know a species is.
So it raises a lot of interesting questions
about what do we care to conserve.
An individual that we know is a blue spotted salamander
or their genetic legacy?
People argue about what a species is.
And these animals are so far from that argument,
that it's not even worth having it.
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