A team of Japanese researchers has achieved something incredible: they've captured, for the first time ever, a movie which shows how thoughts form in the brain. OK, so it's a thought forming in the brain of a zebrafish.
According to a new study conducted by ichthyologists Dr Ralf Britz of the Natural History Museum and Dr David Johnson of the Smithsonian National Museum of Natural History, the skeleton of the sharksucker fish’s disc is formed in development through the expansion of both the bases of the dorsal fin spines and the distal radial elements of the fin supports.
Sharksucker fish with its unusual sucking disc on its head (Dave Johnson)
Sharksuckers, also called remoras, are a group of 8 species in the fish family Echeneidae. They are the only fish with a sucking disc. Their closest relatives are the cobia and dolphin fish.
Sharksuckers use the spines and suction of their sucking disc to attach themselves to large marine animals. They don’t seem to cause any harm, or benefit, to the animal they’re attached to, and they live off scraps of food, faeces or parasites from the larger animal. Some people are known to use sharksuckers to catch other fish, throwing them into the sea attached to a fishing line and pulling them in once they are attached to a larger sea animal.
The ichthyologists investigated how the sucking disc develops in larval fish of the genus Remora. They took snapshots of the developmental stages, staining the bones red to see changes more clearly.
To see whether the sucking disc is created from the existing dorsal fin that most other fish have, they looked at how the dorsal fin developed in the same early stages in another fish, of the genus Morone(temperate basses), which has a typical dorsal fin as an adult consisting of spinous and soft dorsal fin parts. They compared the two.
Such comparisons help to establish whether structures in different species have the same evolutionary origin despite looking and functioning differently. Up to a certain stage in the fishes development, the dorsal fin can be seen developing in the same way and looking very similar in both fishes. Then, over a series of small changes, the dorsal fin in the Remora begins to expand and shift towards the head.
By the time the Remora has reached around 30 mm in length, the dorsal fin has become a fully formed 2 mm sucking disc. It still has the components found in the dorsal fin, the tiny fin spines, spine bases and supporting bones, but the spine bases have greatly expanded. So, the sucking disc is formed by a massive expansion of the dorsal fin through small changes while the fish is developing. It is not the result of the evolution of a completely new structure.
“What keeps impressing me when I study the development of some of the weirdest structures in the fish world is that natura non facit saltus, ‘nature does not make jumps,’ and even the strangest anatomical modifications happen through small gradual changes in development,” said Dr Britz, whoreported the findings in the Journal of Morphology.
Researchers at The Rockefeller University and Paris University have found that when a C. biroi ant steps out of line and attempts to lay eggs when it shouldn't, the other ants will drag it out of the nest and bite and sting it until it dies. And in a new study published this month in Current Biology, they believe they've discovered why. Rather than being a competitive behavior between ants over who gets to reproduce more, it appears the killing is a means of keeping the whole colony functioning properly. It's a mechanism, the researchers say, that parallels processes in other areas of biology, even inside a single individual—like when the body attacks cancer cells proliferating out of control.
Daniel Kronauer, head of the Laboratory of Insect Social Evolution at Rockefeller, and his colleagues in Paris chose to study C. biroi because of the special characteristics it has. For one, each worker ant in the species can lay eggs—there are no queens. Also, each of its colonies is made up of ants that are genetically identical. All this makes these ant-killings even more surprising. From an evolutionary perspective, there shouldn't be conflict over who gets to reproduce—with each ant being genetically equal, there's no motivation for reproductive dominance.
The researchers monitored 11 C. biroi colonies for 13 months. The ants have a reproductive cycle whereby the whole colony produces eggs at the same time and once the larvae hatch from the eggs, the ants stop laying eggs and begin to forage for food to feed the hungry larvae. The researchers observed the executions when errant ants would continue to produce eggs while others were off looking for food. Several ants would ambush the perpetrator and bite and sting it for several hours or even days until it died. Upon dissection, Serafino Teseo, a graduate student at Paris University, and his colleagues found that the ants that rebelled had a high number of ovarioles, meaning they had a greater capacity for reproduction. They were also found to be about one month old, indicating that the discretion occurred following their first reproductive phase, when their ovaries were activated for the first time. "It appears this is an evolutionary mechanism to eliminate individuals who do not respond properly to the normal social cues that tell the ants when to start laying eggs and when to stop," says Kronauer. Kronauer's lab is interested in illuminating the processes that allow simple biological units to cooperate and form more complex higher-level units. Ant and bee colonies are often described as "super-organisms," because the individual insects cooperate to create an efficient higher-level entity, much as the different cells of a body work together to keep a person alive. "This system in C. biroi shows striking analogies to immunosurveillance on cancer cells," says Kronauer. "In both cases, the individuals—single ants and cells, respectively—that are not responsive to regulatory signals proliferate uncontrollably and are attacked and removed to protect the higher-level unit. It's a fascinating example of how evolution converges on analogous solutions to similar problems at different levels of biological organization."
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