Research Highlights

Our pick of the latest scientific literature

  • Volume 549
  • Issue 7671

Brain

More than one mechanism may underlie memory and learning

The brain seems to form some memories as sequences of events, rather than by coordinated firing of interconnected neurons.

Neuroscience dogma has long held that memories are formed when networks of neurons in the brain fire all at once, strengthening the connections between them. But this may not always be the case.

Jeffrey Magee at the Howard Hughes Medical Institute in Ashburn, Virginia, and his colleagues recorded neuronal activity in the hippocampus — the area of the brain that controls memory — in mice running on a treadmill. The team found that brain-activity patterns associated with forming memories of a place occurred over several seconds, rather than milliseconds, as previously thought. 

The finding suggests that the brain uses a different, as-yet-unknown mechanism to store memories of chunks of time — effectively a new type of learning. This could allow animals to store an entire sequence of events, or to better learn important information, such as the location of a reward, the scientists say. 

The most daring individuals lead schools of sticklebacks.

The most daring individuals lead schools of sticklebacks. Frans Lemmens/Alamy

Zoology

Bold fish run the school

Sticklebacks’ ‘personalities’ control group dynamics

Individual differences in behaviour, such as boldness and sociability, are common in animals, but how these ‘personalities’ affect group behaviour has remained poorly understood. 

Jolle Jolles at the University of Cambridge, UK, and his colleagues observed the behaviour of individual sticklebacks (Gasterosteus aculeatus) in a tank, and then filmed shoals swimming freely and foraging in different environments. Fish that were consistently more sociable tended to swim more slowly and cluster with other fish, while less-sociable fish were more likely to lead the shoal.

When the tank contained hidden patches of food or a refuge, the bolder, more-exploratory fish increased group foraging performance. Using a computer simulation of shoals containing a mix of personality traits, the team found that the same group dynamics emerged. Consistent individual differences in behaviour can affect the structure, leadership and performance of animal groups, the authors say. 

Antibiotics

Uneaten fish food poses a risk to public health

Antibiotic-resistance genes may transfer between bacteria accumulating on the seabed.

Fish food used in marine farming on the open ocean provides a vehicle for the accumulation of bacteria with antibiotic-resistance genes (ARGs) in sea-floor sediment.

Jing Wang and his colleagues at the Dalian University of Technology in China analysed five fishmeal products — two from Peru and one each from China, Russia and Chile. They detected a total of 132 ARGs.

When fishmeal is distributed at marine fish farms, most of it sinks to the sea floor uneaten and introduces new bacteria to the sediment, which is a hotbed for microbial communities to exchange genes. If ARGs enter the food chain through contaminated seafood, the genes could be transferred to bacteria that cause human diseases, potentially contributing to the rise of drug-resistant pathogens. 

To combat the problem, the researchers say that fishmeal should be screened for ARGs during food-safety inspections.

Particle physics

New particle has twice the charm

Scientists have detected a subatomic particle that contains two charm quarks, the first unambiguous detection of such a particle.

Baryons — the particles that make up normal matter — are formed of quarks held together by gluons. Quarks come in both light (up, down and strange) and heavy (top, bottom and charm) varieties. But all previously found baryons contain, at most, one heavy quark. 

Using the Large Hadron Collider at CERN, the particle-physics laboratory near Geneva, Switzerland, the LHCb Collaboration detected an energy signature from a cascade of decaying particles that indicated the existence of a parent particle with two charm quarks and an up quark. The particle, called cascade-c-c-double-plus, is the first to be confirmed as having two heavy quarks.

Previously, another group reported a tentative detection of cascade-c-c-plus, which contains two charm quarks and a down quark. However, the two particles have a difference in mass that is much higher than predicted. The LHCb Collaboration hopes to confirm this detection and so shed light on the situation.

The seldom-heard call of the female cuckoo puts other birds on edge.

The seldom-heard call of the female cuckoo puts other birds on edge. Nature Production/NPL

Animal behaviour

The cuckoo's double deception dupes its hosts

Female cuckoos mimic bird of prey to misdirect the attention of host parents.

After parasitizing a nest, female common cuckoos often mimic the frightening calls of a hawk to divert host parents’ attention.

During field experiments, Jenny York and Nicholas Davies at the University of Cambridge, UK, found that reed warbler (Acrocephalus scirpaceus) hosts did not pay much attention to the simple two-tone call of male common cuckoos (Cuculus canorus). But the hawk-like chuckle call of the female worked wonders to distract the warblers from spotting the cuckoo eggs in their clutch.

Female cuckoos’ deceptive skills are an example of how parasites can manipulate the behaviour of the host species to their own advantage, the researchers say. The field experiments showed that this means of distracting warbler parents increased cuckoos’ parasitic success. 

Animals such as the bobtail squid can change colour thanks to their adoption of a bacterial gene.

Animals such as the bobtail squid can change colour thanks to their adoption of a bacterial gene. Getty

Genetics

How sea creatures change their colour

Protean creatures owe their skills to a bacterial gene.

Cephalopods such as octopuses, cuttlefish and squid can instantly change their body colour using proteins called reflectins. A study shows that these proteins originated in bacteria that live in symbiosis with the animals.

Can Xie at Peking University in Beijing and his colleagues searched the genome sequence of the bioluminescent bacterium Vibrio fischeri for matches to the reflectin gene sequence from the common cuttlefish (Sepia officinalis). The bacterium lives symbiotically inside many marine animals. The scientists detected two matches to the cuttlefish reflectin gene, suggesting that it was transferred horizontally from the bacterium to ancient cephalopods. 

Using chromatography and electron microscopy, the team found that reflectin proteins self-assemble into ‘bricks’, which are further organized into reflective platelets in cephalopod skin by chemical messengers such as neurotransmitters. Evolution has elaborated on the bacterial gene to produce a family of reflectin proteins that give cephalopods their remarkable colour-changing abilities. 

Astronomy and astrophysics

Black hole spotted in the centre of the Milky Way

A black hole 100,000 times the mass of the Sun seems to be lurking near the core of our Galaxy.

Astrophysicists have long theorized the existence of supermassive black holes at galactic cores, built by successive mergers of intermediate-mass black holes, but no such objects have yet been confirmed. Tomoharu Oka of Keio University in Yokohama, Japan, and his colleagues used the ALMA radio telescope in Chile to observe a cloud of molecular gas that previous observations had suggested contained fast-moving gas swirling around a small object. ALMA’s high-resolution images revealed a point-like source of radio-wave emission and a clump of gas at its centre — consistent with a black hole roughly 100,000 times as massive as the Sun.

The black hole could be the remnant of a dwarf galaxy that was swallowed up by the Milky Way, lending credence to the merger scenario of supermassive-black-hole formation, the authors suggest.

Analyses of human skeletons suggest many women moved to Germany’s Lech River valley during the Bronze Age.

Analyses of human skeletons suggest many women moved to Germany’s Lech River valley during the Bronze Age. Stadtarchäologie Augsburg

Anthropology

Migrant women drove change in Bronze Age central Europe

Female mobility may have been crucial to cultural transformation.

Several cultures appeared in central Europe from about 5,000 years ago, but it is not clear whether this happened as a result of migration, cultural change, or both.

Corina Knipper at the Curt Engelhorn Center for Archaeometry in Mannheim, Germany, and her colleagues examined 84 skeletons dating from 2,500 BC to 1,700 BC, recovered from the Lech River valley in southern Germany. Artefacts buried with them were characteristic of either the Bell Beaker culture or the early Bronze Age culture that followed. 

Compared with those from the Bell Beaker period, the early Bronze Age skeletons had more diverse mitochondrial DNA, which is inherited through the maternal line. An analysis of strontium and oxygen isotopes, which relate to where a person lived when their adult teeth formed, suggests that 60% of the females who lived in the Lech Valley came from elsewhere, compared with only 11% of the males. 

This suggests that women carrying distinct mitochondrial markers moved into the region, bringing fresh cultural practices with them, the authors say.

Historical nautical charts of the Florida Keys include historical coral references.

Historical nautical charts of the Florida Keys include historical coral references. Loren McClenachan

Ecology

Ancient maps reveal dramatic coral loss

British navy charts provide missing data that could be vital to ecologists.

British maps from the eighteenth century attest to dramatic losses of coral from Florida’s inshore reefs. 

Loren McClenachan at Colby College in Waterville, Maine, and her colleagues analysed detailed maps of Florida coasts prepared by British navy mappers between 1773 and 1775. They found 143 recordings of coral on two charts covering an area stretching roughly 180 kilometres, from Key Largo to the Marquesas Keys. Comparing these charts with modern data, the team estimates that 52% of the reefs have been lost since the 1770s. 

Offshore areas were largely intact, but reefs near land and in Florida Bay had been severely depleted — with some vanishing entirely. Modern surveys could miss the disappearance of entire reefs, because they generally focus on known, current coral ranges, say the authors.

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