Evolution happening before our eyes

The Hadal zone is a region of the ocean so deep that it was named after Hades itself, and can reach up to 11km at its lowest point. But even so, there’s still life at these depths. And a new study of this hard to reach region has revealed an exciting opportunity to observe the evolution of a new species. A species of shrimp-like creatures called amphipods have been found to be living in 11 distinct groups at these extreme depths, isolated by the shallower waters between them. These amphipod groups were found to be genetically identical, but they are so isolated that their groups never mix. So are they splitting off to form new species? Johanna Weston, from the Woods Hole Oceanographic Institute, has been speaking to Will Tingle about what the future may hold down in the depths...

Johanna - We're getting a snapshot to see kind of evolution and speciation happen. So while it's the same species right now, these different populations aren't interbreeding and so they're on their way to becoming different species. So even though they were the same species, we're showing that they're actually very isolated into each one of these Hadal zones.

Will - And we'd assume that any speciation or any change that these arthropods would undergo is gonna be far longer than our natural lifetimes. We're probably not gonna see its effects within the next 10 years.

Johanna - Yeah. So we're talking about scales of millions of years but what we're doing is seeing a snapshot in time. What's exciting about this study is this is the first time, um, that we've been able to gather a global specimen collection and then actually be able to test these questions that have really been plaguing us as scientists since the Hadal zone was first studied in the 1950s. So for us as Hadal biologists, this is a really exciting step forward in our field.

Will - And you say that there's not only a very low amount of genetic differences between these populations, but also a very small amount of gene flow. They're not really interacting with each other. Is it therefore that the reason they're so similar is because the conditions down in the Hadal zone are so uniform that there's no real reason for any one particular isolated population to need to adapt to anything?

Johanna - That's definitely a good hypothesis and we're not able to get a clear answer on that in this study. But I think that does play a role. So the two populations that were most different was the Atacama trench and the South Sandwich trench population. And the Atacama trench population seemed to be different enough to suggest it was a very similar but different species. And so the Hadal zone is about one to two degrees Celcius, not a lot of food, really high pressure. And it has, as you said, most places have a similar environment. The Atacama trench and the South Sandwich trench are unique in that the Atacama trench has actually a lot of food input and we're learning that it has really low dissolved oxygen. And so its condition is slightly different, which might push selection towards speciation. And then South Sandwich trench is a really interesting system as well, because it's one of the few trenches where the temperatures down there are actually below zero. And so again, there might be that extra cold temperature might be accelerating diversification as well.

Will - This is all postulation, of course,

Johanna - It is all postulation. It's really exciting to be able to postulate these things now.

Will - In the last few years, I feel the general public and maybe even governments have started to shift their attitudes towards the sea as being a place that needs immediate conservation. We see these beautiful dolphins and coral reefs, and we think we need to save the ocean, but we don't pay much attention to the real deepest parts of the ocean. So how does this study hope to shine a light on the Hadal zone species?

Johanna -The Hadal zone, it's very hard to get to technologically, logistically it feels really far, like 11,000 meters is a long way down. It takes about four hours in a submarine. And so it gives this perception of remoteness. But in a number of studies we're learning that this remoteness is actually not protecting the Hadal zone from us. So we're learning that there's high amounts of plastic pollution where animals are actually inadvertently ingesting plastic fibers. There's high levels of PCBs. There's high levels of anthropogenic mercury. And so this remoteness isn't protecting them or shielding them from us. So I think as we start to talk about deep sea conservation, we really need to bring the Hadal zone into that conversation and make sure that we're not just protecting coral reefs, but we're also protecting the deepest parts of our ocean as well.