"Long before it's in the papers"
August 03, 2015


In earliest complex life forms, a clever reproductive strategy discerned

Aug. 3, 2015
Courtesy of the University of Cambridge
and World Science staff

The old­est known com­plex life forms may have had a sur­pris­ingly soph­is­t­icated mode of re­pro­duc­tion, sug­gests a pa­per pub­lished in Na­ture this week. 

The find­ing may shed light on the mys­te­ri­ous Edi­a­ca­ran bi­o­ta, a weird and won­der­ful col­lec­tion of or­gan­isms that lived around 565 mil­lion years ago. One of these was Fracto­fusus, a sea­floor-dwel­ling or­gan­ism made up of fern-like fronds with frac­tal char­ac­ter­is­tics—pat­terns that re­ap­pear at dif­fer­ent size scales.

Close-up of a Fracto­fusus from Mis­tak­en Point, New­found­land, Can­a­da, show­ing many "self-simi­lar" branch­es. This type of branch­ing is unique to the Edi­a­car­an, and makes un­der­stand­ing the bi­ol­o­gy of Frac­to­fus­us hard. (Cred­it: E.G. Mitch­ell)

Quite un­like an­y­thing alive to­day, lit­tle is known about even its most bas­ic bi­ol­o­gy, al­though some con­sid­er it to have been among the first an­i­mals. It how­ev­er seems to lack a mouth, or­gans, or a way of mov­ing, and is thought to have just ab­sorbed nu­tri­ents around it.

From an anal­y­sis of fos­sils from New­found­land, Can­a­da, Emily Mitch­ell of the Un­ivers­ity of Cam­bridge and col­leagues ar­gue in the study that Fracto­fusus could switch be­tween two re­pro­duc­tive modes.

First, it could pro­duce wa­ter­borne propag­ules, or seed-like ob­jects, that drift in the cur­rent, en­a­bling co­lon­iz­a­tion of new ar­eas. 

Hav­ing sent out an “ad­vance par­ty” to set­tle a new ar­ea, the find­ings sug­gest, Fracto­fusus could quickly pop­u­late the neigh­bor­hood by pro­duc­ing “runner”-like struc­tures. These are long, hor­i­zon­tal stems that could pro­duce new in­di­vid­u­als at reg­u­larly spaced points. Straw­ber­ry plants repro­duce in a si­m­i­lar way. 

The meth­od would have en­abled the or­gan­ism to repro­duce asex­u­ally and spread across the sea floor, ac­cord­ing to the re­search­ers.

The find­ings, re­ported to­day in the research jour­nal Na­ture, could help re­veal the ori­gins of our mod­ern ma­rine en­vi­ron­ment, the sci­en­tists said.

Mitch­ell and col­leagues used sta­tis­ti­cal tech­niques to as­sess the dis­tri­bu­tion of popula­t­ions of Fracto­fusus. The re­search­ers no­ticed that larg­er in­di­vid­u­als, which they likened to “grand­par­ents,” were ran­domly spread out. Sur­round­ing them were dis­tinct pat­terns of smaller “par­ents” and “chil­dren.” 

Artist's impression of Fractofusus community (Courtesy U. of Cam­bridge)

The pat­terns strongly re­sem­ble the clus­ter­ing seen in mod­ern plants, and sug­gest the “grand­par­ents” grew from propag­ules while the later gen­er­ations grew from run­ners, Mitch­ell and col­leagues said.

Reprod­uction in this way made “range­o­morphs,” a cat­e­go­ry of or­gan­isms of which Fracto­fusus was one, “highly suc­cess­ful, since they could both co­lonies new ar­eas and rap­idly spread once they got there,” said Mitch­ell. 

“The ca­pa­city of these or­gan­isms to switch be­tween two dis­tinct modes of re­pro­duc­tion shows just how soph­is­t­icated their un­der­ly­ing bi­ol­o­gy was, which is re­mark­a­ble at a point in time when most oth­er forms of life were in­credibly sim­ple.”

Al­though range­o­morphs weren’t the first mul­ti­-celled crea­tures, they pre­date the so-called Cam­bri­an Pe­ri­od be­gin­ning about 540 mil­lion years ago. Only at that stage does the fos­sil rec­ord yields an­ces­tral rep­re­sen­ta­tive of most of the ma­jor groups of an­i­mals seen to­day.

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The oldest known complex life forms may have had a surprisingly sophisticated mode of reproduction, suggests a paper published in Nature this week. The finding may shed light on the mysterious Ediacaran biota, a weird and wonderful collection of organisms that lived around 565 million years ago. One of these was Fractofusus, a sea organism made up of fern-like fronds with fractal characteristics—patterns that reappear at different sizes. Quite unlike anything alive today, little is known about even its most basic biology, although some consider it to have been among the first animals. It however seems to lack a mouth, organs, or a way of moving, and is thought to have just absorbed nutrients around it. From an analysis of fossils from Newfoundland, Canada, Emily Mitchell of the University of Cambridge and colleagues suggest that Fractofusus could switch between two different reproductive modes. First, it could produce waterborne propagules, or seed-like objects, that drift in the current, enabling colonization of new areas. Having sent out an “advance party” to settle a new area, the findings suggest, Fractofusus could quickly populate the neighborhood by producing “runner”-like structures. These are long, horizontal stems that could produce new individuals at regularly spaced points. Strawberry plants reproduce in a similar way. The method would have enabled the organism to reproduce asexually and spread across the sea floor, according to the researchers. The findings, reported today in the journal Nature, could help reveal the origins of our modern marine environment, the scientists said. Mitchell and colleagues used statistical techniques to assess the distribution of populations Fractofusus. The researchers noticed that larger individuals, which they likened to “grandparents,” were randomly spread out. Surrounding them were distinct patterns of smaller “parents” and “children.” The patterns strongly resemble the clustering seen in modern plants, and suggest the dual mode of reproduction—the “grandparents” being the product of propagules, while the others growing from the stem-like runners. Reproduction in this way made “rangeomorphs,” a category of organisms of which Fractofusus was one, “highly successful, since they could both colonies new areas and rapidly spread once they got there,” said Mitchell. “The capacity of these organisms to switch between two distinct modes of reproduction shows just how sophisticated their underlying biology was, which is remarkable at a point in time when most other forms of life were incredibly simple.” Although rangeomorphs weren’t the first multi-celled creatures, they predate the so-called Cambrian Period beginning about 540 million years ago. Only at that stage does the fossil record yields ancestral representatives of most of the major groups of animals seen today.