New Scientist - USA (2020-01-25)

16 | New Scientist | 25 January 2020

WE ARE beginning to better

understand the single-celled

organisms that may be the

ancestors of all complex life.

Last year, Hiroyuki Imachi

at the Japan Agency for

Marine-Earth Science and

Technology and his colleagues

isolated a strain of Asgard archaea

and grew it in a lab for the first

time. That achievement has

now been published (Nature,

doi.org/gghwjg), and a slew

of recent studies is giving us

more insight into the features

of our possible ancestor.

The first Asgard archaea

were described in 2015 after their

DNA was found in sediments on

the Atlantic seabed. Biologists

immediately recognised that they

could help explain one of the most

important steps in evolutionary

history: the origin of eukaryotes.

Bacteria and archaea are

both old, single-celled branches

of life with simple internal

structures. But all multicellular

organisms are eukaryotes, which

have larger, more intricate cells

that evolved more recently.

While the Asgard microbes

are archaea, they carry genes

previously found only in

eukaryotes. This implies that

billions of years ago, eukaryotes

evolved from an Asgard archaeon.

The link between them looks

increasingly solid. In December,

Tom Williams at the University

of Bristol, UK, and his colleagues

analysed more than 3000 gene

families in archaea and

eukaryotes. They confirmed

that Asgard archaea are the closest

known relatives of eukaryotes

(Nature Ecology & Evolution,

doi.org/ggd7k4).

The most crucial feature of

eukaryotes is mitochondria:

sausage-shaped structures

within the cells that provide

energy. Mitochondria were once

bacteria, which were somehow

engulfed by a eukaryotic cell.

The cultured Asgard archaeon,

Prometheoarchaeum, hints at how

this happened. When Imachi and

his colleagues grew it, they saw

long, tentacle-like protrusions (see

inset image, left). The team

suggests that Asgard archaea

cooperated with bacteria, which

first lived swaddled in these

protrusions, before ultimately

moving inside the Asgard cells.

Robert Robinson at Okayama

University in Japan and his team

found that Asgard archaea also

have mechanisms for assembling

and breaking down a protein

called actin (bioRxiv, doi.org/

gf8bfc). This forms struts within

cells and plays a key role in

enabling membranes to swallow

other cells. Robinson says the

Asgard archaea probably use

actin to grow their protrusions.

This can’t explain everything,

says Purificación López-García

at the French National Centre for

Scientific Research. She says the

outer membranes of eukaryotes

resemble those of bacteria, not

archaea. Many eukaryotic genes

also come from bacteria. She

suspects that more than two

types of microorganism

contributed to eukaryotes. ❚

Find out more about our

long-lost microbial ancestors

in next week’s issue.

Biology

Michael Marshall

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News

Deep-sea vehicles have

discovered Asgard archaea

(inset) in sediments

Conservation

Many orangutans

released into the

wild don’t survive

THE number of Bornean orangutans

is dwindling, and there is little

evidence that efforts to relocate

them from risky areas or

rehabilitate those in captivity

bolster their population.

Between 2007 and 2017, about

1200 Bornean orangutans (Pongo

pygmaeus) were released into

natural forests in Kalimantan, the

Indonesian part of Borneo. Nearly

500 of those were formerly captive

and nursed back to health before

being released. But it is unclear how

many of these animals are still alive.

To make these estimates,

Julie Sherman at Wildlife Impact

in Oregon and her team reviewed

studies, news stories and public

data on conservation efforts. They

also collected data from rescue

centres, government agencies and

zoos on the outcomes of relocation

or rehabilitation for these apes.

The few cases where orangutans

were tracked for more than three

years suggest that fewer than

30 per cent of the released animals

may have survived.

During the study period, at least

620 wild orangutans were also

picked up outside protected areas

in Kalimantan and released into a

different wild site, mainly to prevent

potential conflict with people.

“The assumption translocation

practitioners make is that since

these are wild orangutans, they will

survive anywhere in the wild,” says

Sherman. Again, the fate of such

animals usually isn’t monitored.

The researchers found that, in

most cases, people weren’t tracking

the impacts of conservation actions

(Biodiversitas, doi.org/djs5).

Their analysis of spending by

145 organisations in 2016 showed

that rescue, reintroduction and

translocation was the predominant

conservation strategy for Bornean

orangutans, with more than

£3.8 million allocated to it.

Instead of improving the

status of this ape, however, the

species went from being classified

as endangered to critically

endangered in 2016. ❚

Shreya Dasgupta

All complex life may have come

from spider-shaped microbes

30%

Proportion of released orangutans

that may survive for three years