the

Pink Lake Mystery Solved!

Extremophiles are some of the weirdest, coolest members of ecosystems -- with adaptations

that allow them to live where very few things can.

Like very salty lakes.

Back in 2013, we made a video about Australia’s Lake Hillier [hilly-er], and talked about

some of the microbes that might be making the water a bright, shocking pink.

At the time, nobody had done a full analysis of exactly what lives in that extremely salty

water.

But now, they have!

The researchers working on the eXtreme Microbiome Project study all kinds of extreme environments,

and when some of them saw our video, they thought this bubblegum-pink, salt-filled lake

might be worth investigating.

So they started trying to identify some of the algae, archaea, and bacteria that make

up Lake Hillier’s microbiome, and presented their findings at a conference last month.

The team collected sediment and water from different parts of the lake, and then performed

what’s known as a metagenomic analysis -- where they extract DNA and use the genetic information

to identify species.

And it turns out that there are all kinds of different salt-loving microbes in the lake.

They did find Dunaliella salina [dun-AY-lee-el-uh say-lee-na], the algae that scientists had

figured would be in Lake Hillier because it’s /also/ present in the equally-rosy Lake Retba

[ret-buh] in Senegal.

The algae produces pigment compounds called carotenoids that help it absorb sunlight,

and also make it look reddish-pink.

But it’s not just the D. salina that gives Lake Hillier its strawberry hue.

The team also found a few species of archaea, as well as a type of bacteria called Salinibacter

ruber.

All of these species are also red-colored, and probably contribute to the pinkness of

the water.

And there were some surprises, too.

One organism that showed up in the lake samples was a bacteria known as Dechloromonas aromatica.

That was unexpected, because D. aromatica is good at breaking down compounds like benzene

and toluene, which are often used in chemical solvents.

And the bacteria is typically found in places that have been contaminated by those solvents.

But it turns out that Lake Hillier was used as a tanning station in the early 1900s -- and

now we have the biological traces to prove it.

So the organisms in a lake can tell you a lot about it, from the science behind its

color to its history.

And an organism’s behavior can tell you a lot about its evolution.

Take humans, for example:

In a study published this week in the journal Nature, two Harvard biologists looked at the

factors that might have contributed to the evolution of the human jaw.

And it turns out that it probably had a lot to do with both meat and stone tools.

See, about 2 million years ago, humans -- specifically, Homo erectus -- evolved smaller, less powerful

jaws.

Which is … weird.

Because Homo erectus had bigger brains and bodies than earlier human ancestors, and would

have needed more energy to sustain themselves.

So if you need more food, why do you have a weaker jaw?

Evolutionary biologists have been thinking about this question for a while, and they

figure that it must have taken Homo erectus less effort to get energy from their food.

And that could either be because of what they were eating, or because of how they prepared it.

By 2.6 million years ago, hominins seem to have been eating meat regularly, and they

were using stone tools by 3.3 million years ago.

It seemed likely that those developments would make it easier to chew -- but until now, no

one had ever tested them.

So, the team fed 34 people four different kinds of foods that would be similar to what

early humans were eating: goat meat, yams, carrots, and beets.

The food came in four different forms: unprocessed, sliced, pounded, and roasted.

While the subjects ate, the researchers monitored how many times they had to chew before swallowing

and how much force they put into chewing.

They found that, per calorie, meat does take less effort to chew than the veggies

humans were probably eating at the time.

And the basic processing methods -- slicing and pounding -- also made it easier to chew

the foods.

The scientists calculated that with a diet that’s 1/3 sliced meat and 2/3 pounded veggies

-- the ratio that’s generally found among foragers in Africa today -- early humans would

have had to chew 17% less often and with 26% less force.

Which could be enough to explain why humans who needed more energy from food to sustain

themselves evolved less powerful jaws.

And! The more complex processing -- roasting -- helped, too. So when it eventually became

common to cook food around 500,000 years ago, that would have made humans even more efficient

eaters.

So … anyone up for some mashed carrots?

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