Enlarge / A photo of Braarudosphaera bigelowii with the nitroplast indicated by an arrowhead. (credit: Tyler Coale )

The complex cells that underlie animals and plants have a large collection of what are called organelles—compartments surrounded by membranes that perform specialized functions. Two of these were formed through a process called endosymbiosis, in which a once free-living organism is incorporated into a cell. These are the mitochondrion, where a former bacteria now handles the task of converting chemical energy into useful forms, and the chloroplast, where photosynthesis happens.

The fact that there are only a few cases of organelles that evolved through endosymbiosis suggests that it's an extremely rare event. Yet researchers may have found a new case, in which an organelle devoted to fixing nitrogen from the atmosphere is in the process of evolving. The resulting organelle, termed a nitroplast, is still in the process of specialization.

Getting nitrogen

Nitrogen is one of the elements central to life. Every DNA base, every amino acid in a protein contains at least one, and often several, nitrogen atoms. But nitrogen is remarkably difficult for life to get ahold of. N ₂ molecules might be extremely abundant in our atmosphere, but they're extremely difficult to break apart. The enzymes that can, called nitrogenases, are only found in bacteria, and they don't work in the presence of oxygen. Other organisms have to get nitrogen from their environment, which is one of the reasons we use so much energy to supply nitrogen fertilizers to many crops.

Enlarge (credit: alex-mit )

Human brains (and the brains of other vertebrates) are able to process information faster because of myelin, a fatty substance that forms a protective sheath over the axons of our nerve cells and speeds up their impulses. How did our neurons evolve myelin sheaths? Part of the answer—which was unknown until now—almost sounds like science fiction.

Led by scientists from Altos Labs-Cambridge Institute of Science, a team of researchers has uncovered a bit of the gnarly past of how myelin ended up covering vertebrate neurons: a molecular parasite has been messing with our genes. Sequences derived from an ancient virus help regulate a gene that encodes a component of myelin, helping explain why vertebrates have an edge when it comes to their brains .

Prehistoric infection

Myelin is a fatty material produced by oligodendrocyte cells in the central nervous system and Schwann cells in the peripheral nervous system. Its insulating properties allow neurons to zap impulses to one another at faster speeds and greater lengths. Our brains can be complex in part because myelin enables longer, narrower axons, which means more nerves can be stacked together.

Enlarge (credit: Carnegie Mellon University )

Until now, when scientists and engineers have developed soft robots inspired by organisms, they’ve focused on modern-day living examples. For instance, we previously reported on soft robot applications that mimicked squid , grasshoppers, and cheetahs . For the first time, however, a team of researchers has now combined the principles of soft robotics and paleontology to build a soft-robot version of pleurocystitid, an ancient sea creature that existed 450 million years ago.

Pleurocystitids are related to modern-day echinoderms like starfish and brittle stars. The organism holds great significance in evolution because it is believed to be the first echinoderm that was capable of moving: It employed a muscular stem to move on the sea bed. But, due to a lack of fossil evidence, scientists never clearly understood how the organism actually used the stem to move underwater. “Although its life habits and posture are reasonably well understood, the mechanisms that control the movement of its stem are highly controversial,” authors of a previously published study focusing on the echinoderm stem note .

The newly developed soft-robot replica (also called the “Rhombot”) of a pleurocystitid has allowed researchers to decode the organism’s movement and various other mysteries linked to the evolution of echinoderms. In their study, they also claim that the replica will serve as the foundation of paleobionics, a relatively new field that uses soft robotics and fossil evidence to explore the biomechanical differences among life forms.

Enlarge (credit: Xinhua Fu)

On one level, we have fireflies figured out. We know the enzyme they use to make light (called luciferase), as well as the chemicals they use in the light-generating reaction. We know them so well that we've turned them into useful tools for studying other aspects of biology, such that lots of people who have never even seen a firefly have used firefly luciferase in the lab.

But on another level, there's a lot we don't understand. Fireflies clearly exercise a level of control over when they light up, and they do so only in specialized organs. And there's nothing like that organ in other species. So, somehow, fireflies evolved an elaborate light-producing organ, and there's no sign of any potential precursors in related species. Which makes it a bit of a mystery.

Now, a pair of researchers from Wuhan, China, (Xinhua Fu and Xinlei Zhu) have started unraveling what's going on at the level of the genes responsible. And, while they haven't produced a complete picture of how evolution built the fireflies, they've brought us a lot closer.