Thanks to Brilliant for
supporting this SciShow video! As a SciShow viewer, you can keep
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annual premium subscription at Brilliant.org/SciShow. You’d be forgiven for assuming that the Arctic and the Antarctic are pretty
similar, ecologically speaking. After all, how different can one frozen
wasteland be from another, really? But as much as we might think of both
places as similar icy cold environments, there are major differences,
aside from the obvious one of just how far apart they are from each other. Given the massive distance between
the Arctic and the Antarctic, you wouldn’t think there’d be a ton
of species that live in both places. But shockingly, there are some
species that do just that. Being members of the same
species means that populations need to be able to mate, and
have gene flow between them. But when it comes to these species,
we’re still trying to figure out just how they manage to
swap genes with individuals at the opposite ends of the Earth. [♪ INTRO] The Arctic and Antarctic regions
are 12,000 kilometers apart at their closest point. Not only are they far apart, the
environments between these poles are extremely different, namely warmer. So it’s hard to imagine a
species so globally widespread that it would survive basically everywhere, from each frosty pole to
the warm waters in between. Species found at both polar regions are
called bipolar, in the geographical sense. A species is bipolar if it has populations higher than the latitude of 55 degrees North or lower than 52 degrees South. But that doesn’t necessarily
mean all bipolar species are only found at these extremes. Take whales. Blue whales, fin
whales, and humpback whales are all found at both poles, but they hang out in the warmer waters between the poles too. Which means we know how they get to
either pole, they just swim there. While these whale migration
distances are obviously impressive, the bigger mystery is how teeny
little creatures like algae, tubeworms, crustaceans, and bacteria
have ended up in two very distant places, especially when they don’t seem
to hang out anywhere in between. This idea of species living at
both poles got a lot of buzz when a survey of marine life, published in 2009, revealed that at least 235 species
were found living in both places. Now, that doesn’t mean the
species referenced in the study were exclusive to the poles. It's also possible that some of the
specimens grouped into one species by this study may actually be multiple
species that just, you know, look alike. Since then, genetic analyses have
revealed that a number of those allegedly bipolar species
should actually be split into separate species across the poles. But other analyses found that
some living things like microbes living in both the Arctic and
Antarctic are shockingly similar. Gene sequencing revealed that these
polar populations were actually more closely related to
each other than they were to microbes living much closer
to them geographically. For example, in 2015, researchers studied
three bipolar species of ciliates, a kind of single-celled microorganism. The researchers determined that two
out of those three ciliates were different enough between polar populations
to be considered separate species. However, they also found that one of
the ciliates species could still breed with individuals from the other pole,
even if they were genetically distinct. And an earlier study from 2007
also found that multiple species of deep sea foraminifera, a different
type of single-celled organism, were genetically very similar to
each other, at both of the poles. There are two possible explanations for this. One is that these foraminifera could
just be really common all over the world, and live in most of the
regions between the poles too, but we just haven’t found them there yet. The other possibility is that, even if
these species aren’t cross-breeding anymore, they may be evolving so slowly that they’re still basically the same genetic species today! So despite being separated
for huge stretches of time, not to mention the thousands
of kilometers of distance, they maintain roughly the same
genetic makeup they’ve had for eons. But conservation of genes isn’t the only
explanation for bipolar species, since there are a few populations still swapping
genes from opposite poles to this day. Take Eurythenes gryllus, a kind of amphipod that was once thought to
be one contiguous species, found in basically any ocean
water deep enough to support it. But a study in 2013 split the species into 9 different lineages that all vary by region. The weird thing was, the samples
of this amphipod from both poles showed very little genetic divergence, despite their genetic diversity
in populations between the poles. That tells us there’s likely
still gene flow going on between these two distant populations. Which means the real puzzle is how they
even get from one location to the other. It’s possible these amphipods,
and a host of other critters, are traveling along an underwater current
called the Antarctic Bottom Water, which begins in the Weddell Sea off
the northern coast of Antarctica and continues along the ocean floor. Of course not all bipolar species
are up for surfing the deep sea, like those that don’t live there to begin with. Those guys might actually be
hitchhiking their way from pole to pole. 23 plant species that have been
identified across the northern hemisphere also grow along the very
southernmost tip of South America. For these plants, there are two proposed
ways they’re getting from A to B. On one hand, there’s the
mountain hopping hypothesis, which predicts these species migrate between different suitable mountain habitats, eventually making their way
down the Rockies and Andes. But only 6 of the 23 bipolar
plant species have been found in any intermediate locations between the poles, so if the other 17 species are leapfrogging, they’re playing hide-and-seek at the same time. So that leaves us with another hypothesis: maybe the plants are being spread
directly from one pole to the other. Long distance dispersal seems
like a literal long shot, but it could happen a number of ways. Their seeds could be carried by
wind, water, or even animals, either by attaching to their ride’s body,
or being eaten and later pooped out. But since the distance is so
massive between these poles, for animals to be carrying the
seeds from one pole to the other would mean the trip would need to be pretty direct and very fast so as not to lose
their, ahem, parcel, too soon. Enter the long distance shorebirds. In a study from 2022, researchers
wanted to identify potential candidates for dispersing these plants, by looking
for birds capable of long-distance flight whose ranges overlapped with where
the bipolar plants were found. They identified that birds called
Hudsonian godwits overlapped the most with the ranges of the bipolar plant
species, followed by the Eskimo curlew. And while their longest continual
flights are off the charts, an incredible 10,000 kilometers without stopping, that still isn’t enough distance
to make the trip from one pole to the other all in one go. So there might be more than one
species involved in getting plants from one pole to the other after all, instead of over a single long-distance delivery. Tragically, the Eskimo
curlew, which was once one of the most common shorebirds in North America, is likely now extinct thanks
to extreme overhunting and habitat destruction on our part. So even if they were once the distributors
of bipolar plants, they aren’t anymore. Regardless of how they’re getting there, these surprising bipolar species are not only showing us the need for further studies, but also helping to sound an alarm
for these fragile frozen environments. For one, climate change appears to be slowing the formation of deepwater currents,
like the Antarctic Bottom Water, which could have huge implications for the global distribution of deep water organisms. But we have only really been exploring
deep sea life at a molecular level since the 1980’s, so we still have a lot to learn. So when it comes to how these
polar populations pull off the long distance sharing of their gene pools, it looks like we’re left with more
questions than answers, at least for now. This SciShow video is supported by Brilliant: the interactive online learning
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