How the first life reproduced

10 August 2015

Interview with

Emily Mitchell, Cambridge University

For billions of years, life on Earth was dominated by simple, single-celled microbes.Fractofusus fossil Then, quite abruptly, about 565 million years ago, something dramatic happened and groups of cells began working together as multicellular organisms. Bur how did this complex early life reproduce? Scientists at Cambridge University have discovered that one of these animals, a seafloor dweller known as Fractofusus, which looked a bit like a fern leaf, appears to have had a dual method of reproducing itself. It could send out runners like a strawberry or spider plant to clone itself locally, and it could send out pieces of itself that could float off and set up new colonies of the organism somewhere downstream. Emily Mitchell explains to Chris Smith...

Chris - Ah! So, you're looking at the individual and you're looking at the community distribution, a sort of spatial distribution on what would have been the sea floor for this big community.

Emily - That's correct. Yes. So, we're looking at all different species, where they lived, and what's the position of them relative to the other fossils, the other species, and also within the species, what that can tell us.

Chris - And how does that give you an insight into how they might reproduce?

Emily - We compared its spatial distribution to what you might expect by random. We knew that if we got a non-random distribution then there's some interesting processes going on. So, we found that actually fractofusus was much, much closer together than you might expect by random.

Chris - In other words, you've got an organism here surrounded by other organisms at too high a density to be explained by - it's just a nice patch of sea floor to live on. So, you're assuming that there must be some kind of reproductive phenomenon going on that's lead to that density that you're observing in that particular area.

Emily - Yes. It's also about the spatial positions of the fossils within the cluster.

Chris - Are they, therefore, spawning a new one off the side of themselves in the same way that my strawberry plant in my strawberry patch will send out a runner and plant another plant next to itself?

Emily - We actually found that when we were looking at the reproduction of fractofusus, that it had a much more complicated reproductive mode than we were expecting. While the vast majority of fractofusus specimens were actually clinging to their parents, produced via stolons or runners of the type you see in strawberry or spider plants. It also had a waterborne propagule stage. So, that is there are little bits of it were released by the parent organisms into the water. And we used the phrase, propagules to describe them, because While they could have been sexually produced seeds or spores, they also might have been very, very tiny fragments or buds. So, what was going on as you had the grandparent specimens, if you will, were producing runners with little clones off the runners. The daughters of the grandparents were then going on to produce more baby fractofususes themselves. And what was really quite a nice part of the study is that when we broke down the sizes of the fractofusus to distinguish between the grandparents, the parents, and the daughters. The distribution of the largest, the grandparent fractofususes, were actually very different. They were randomly distributed on the bedding plane and they also showed current directionality. So, what this tells us is that they were actually formed not as clones but, instead, via waterborne propagules.

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