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Evo­lu­tion


A Col­lec­tion of News by Moos

Evo­lu­tion in the news, arti­cles that stood out and caught my attention.

Moos

201820Jan14:50

Novel hypoth­e­sis on why ani­mals diver­si­fied on Earth

pub­lished 20 Jan­u­ary 2018 | mod­i­fied 20 Jan­u­ary 2018

Can tumours teach us about ani­mal evo­lu­tion on Earth? Researchers believe so and now present a novel hypoth­e­sis of why ani­mal diver­sity increased dra­mat­i­cally on Earth about half a bil­lion years ago. A bio­log­i­cal inno­va­tion may have been key.

The find­ings of a trans­dis­ci­pli­nary and inter­na­tional team, from Lund Uni­ver­sity in Swe­den and Uni­ver­sity of South­ern Den­mark are pub­lished online on 18 Jan­u­ary in Nature Ecol­ogy & Evo­lu­tion.

The new hypoth­e­sis holds that the dra­matic diver­si­fi­ca­tion of ani­mals resulted from a rev­o­lu­tion within the ani­mals’ own biol­ogy, rather than in the sur­round­ing chem­istry on Earth’s surface.

Life on Earth was dom­i­nated by microbes for roughly 4 bil­lion years when mul­ti­cel­lu­lar life sud­denly – then in the form of ani­mals in robust ecosys­tems – made a vig­or­ous entry. Why ani­mals diver­si­fied so late and so dra­mat­i­cally has remained unre­solved and is a mat­ter of hot debate.

The diver­si­fi­ca­tion of ani­mals occurred over a geo­log­i­cally short period of time and is known as the Cam­brian explo­sion. Many geol­o­gists have assumed that the Cam­brian explo­sion was trig­gered by an increase of atmos­pheric oxygen.

How­ever, a causal rela­tion­ship between the Cam­brian explo­sion and increas­ing atmos­pheric oxy­gen lacks con­vinc­ing evidence.


(Source: Shape of Life on Vimeo; see also Cam­brian explo­sion on Shape of Life)

His­toric focus on high oxy­gen
Indeed, research over the last years weaken the sup­port for a cor­re­la­tion between the Cam­brian explo­sion and increas­ing atmos­pheric oxy­gen. For exam­ple, dra­matic changes in atmos­pheric oxy­gen are noted both before and after the Cam­brian, but not specif­i­cally when ani­mal diver­si­fi­ca­tion took off.

Sim­ple ani­mals are fur­ther­more noted to require sur­pris­ingly low oxy­gen lev­els, which would have been met well before the Cambrian.

A heated hunt for the geo­chem­i­cal evi­dence that oxy­gen increased when ani­mals diver­si­fied goes on but, after decades of dis­cus­sion, it seems worth­while to con­sider the devel­op­ment of mul­ti­cel­lu­lar­ity also from other angles”, says geo­bi­ol­o­gist Emma Ham­mar­lund, PhD and researcher at the divi­sion for trans­la­tional can­cer research at Lund Uni­ver­sity and guest researcher at the Nordic Cen­ter for Earth Evo­lu­tion at the Uni­ver­sity of South­ern Denmark.

Tumours are suc­cess­ful ver­sions of mul­ti­cel­lu­lar­ity, also at low oxy­gen
In order to under­stand more about the con­di­tions for mul­ti­cel­lu­lar life, Emma Ham­mar­lund con­tacted tumour biol­o­gist, Pro­fes­sor Sven Påhlman at the Depart­ment of Lab­o­ra­tory Med­i­cine at Lund Uni­ver­sity, who has explored the impor­tance of low oxy­gen con­cen­tra­tions, or so-​called hypoxia, in the tumour set­ting for nearly two decades.

I wanted to learn what tumour sci­en­tists observe on a daily basis, in terms of tis­sue growth and how it relates to oxy­gen. Tumours are after all, and unfor­tu­nately, suc­cess­ful ver­sions of multicellularity.

Emma Ham­mar­lund, lead author, Nordic Cen­ter for Earth Evo­lu­tion, Uni­ver­sity of South­ern Den­mark, Odense, Den­mark; and Trans­la­tional Can­cer Research, Depart­ment of Lab­o­ra­tory Med­i­cine, Lund Uni­ver­sity, Lund, Sweden

The team, includ­ing also tumour biol­o­gist Dr. Kristof­fer von Ste­d­ingk at Lund University’s Pae­di­atrics divi­sion, tack­led the his­toric ques­tion of why ani­mals devel­oped so late and dra­mat­i­cally with novel clues from the field of tumour biology.

A shared suc­cess fac­tor
Specif­i­cally, they tested whether the same mol­e­c­u­lar tools exploited by many tumours – to main­tain stem cell prop­er­ties – could also be rel­e­vant to the suc­cess of ani­mals in the Cam­brian explosion.

Cells with stem cell prop­er­ties are vital for all mul­ti­cel­lu­lar life in order to regen­er­ate tis­sue. For exam­ple, cells in the wall of human small intes­tine are replaced every 24 days, through the divi­sion of stem cells.

Hypoxia is gen­er­ally seen as a threat, but we for­get that oxy­gen short­age in pre­cise peri­ods and set­tings also is a pre­req­ui­site for mul­ti­cel­lu­lar life. Our stem cells are the ones that form new tis­sue, and they are extremely sen­si­tive to oxy­gen. The stem cells there­fore have var­i­ous sys­tems for deal­ing with the effects of both oxy­gen and oxy­gen short­age, which is clear in the case of tumours”, explains Sven Påhlman.

These sys­tems involve a pro­tein that can ‘fool’ cells act as if the set­ting was hypoxic. This can also fool cells to get stem cell-​like properties.

Tumour cells cope with oxy­gen
By study­ing the abil­ity of tumour cells to imi­tate the prop­er­ties of stem cells, Sven Påhlman’s team have observed how tumour cells can high-​jack spe­cific mech­a­nisms that evade the neg­a­tive effects that high oxy­gen has on stem cells. As a con­se­quence, the tumour cells are able to main­tain stem cell prop­er­ties, despite being sur­rounded by the high oxy­gen con­cen­tra­tions that are present in the body.

This same abil­ity, accord­ing to the authors, is one of the keys that also made ani­mals so successful.

The abil­ity to con­struct stem cell prop­er­ties despite high oxy­gen lev­els, so called ‘pseudo­hy­poxia’, is present also in our nor­mal ver­te­brate tis­sue. There­fore, we flip the per­spec­tive on the oxic set­ting: While low oxy­gen is gen­er­ally unprob­lem­atic for ani­mal cells, the oxic set­tings pose a fun­da­men­tal chal­lenge for com­plex mul­ti­cel­lu­lar­ity. With­out addi­tional tools, the oxic set­ting makes tissue-​specific stem cells mature too early”, says Sven Påhlman.

A bio­log­i­cal rev­o­lu­tion
The new hypoth­e­sis that gives credit to a bio­log­i­cal inno­va­tion to have trig­gered ani­mal diver­si­fi­ca­tion is sim­i­lar to how we think of bio­log­i­cal inno­va­tions chang­ing life in the past. Just the pres­ence of free oxy­gen is the result of some microbes find­ing a way of using sun­light to get energy. This was also a bio­log­i­cal event.

A view that fits with other geo­bi­o­log­i­cal obser­va­tions, such that envi­ron­ments with ‘enough’ oxy­gen have been present on Earth since long before the Cam­brian explosion.

The hypoth­e­sis also has impli­ca­tions for how ani­mals may have vary­ing capac­i­ties to live in oxy­genated envi­ron­ments, and per­haps even for how we see can­cer as an evo­lu­tion­ary con­se­quence of our abil­ity to live in oxy­genated niches.

Bring­ing geo­bi­ol­ogy and can­cer research together
Tak­ing an evo­lu­tion­ary approach is unusual for can­cer researchers, even though the devel­op­ment of tumours is gen­er­ally seen as an evo­lu­tion­ary process.

Sim­i­larly, geo­bi­o­log­i­cal research rarely apply the cel­lu­lar per­spec­tive. But hav­ing com­bined their exper­tise, both Emma Ham­mar­lund and Sven Påhlman are sur­prised that we have not pre­vi­ously won­dered about our para­dox­i­cal abil­ity to renew tis­sue in the oxic setting.

Surely, many peo­ple [who, sic] would intu­itively dis­agree. But once you flip the per­spec­tive on the oxic niche and start to con­sider it as chal­leng­ing for stem cell prop­er­ties and tis­sue renewal, then puz­zling obser­va­tions from dis­tant fields starts to fit together. And you can’t turn back”, con­cludes Sven Påhlman.

(Source: Lund Uni­ver­sity press release, 18.01.2018)


Goal: 7000 tigers in the wild

Tiger range countries map

Tiger map” (CC BY 2.5) by Sander­son et al., 2006.

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