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As a SciShow viewer, you can keep  building your STEM skills with a 30 day free trial and 20% off an  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 deep water 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  platform with thousands of lessons to choose from in math,  science, and computer science.

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