The 5 most popular scientific papers of March 2021 in the Nature Index journals

A self-decapitating sea slug and strategies for mitigating wildlife predation by house cats feature in these widely discussed studies.

  • Bec Crew

Factors such as diet and play can make cats less likely to hunt wildlife, according to a popular study. Credit: Chris Winsor/Getty Images

The 5 most popular scientific papers of March 2021 in the Nature Index journals

A self-decapitating sea slug and strategies for mitigating wildlife predation by house cats feature in these widely discussed studies.

28 June 2021

Bec Crew

Chris Winsor/Getty Images

Factors such as diet and play can make cats less likely to hunt wildlife, according to a popular study.

March’s most talked-about natural-sciences papers explore the possibility of lightning bolts as a source of an essential building block of life, and the development of iBlastoids, a new cellular structure designed for the study of early human development.

Also featured are observations of whole-body regeneration in certain species of sea slugs and non-invasive methods for curbing wildlife harm by house cats.

The sole COVID-19-related study in the list relates to immune responses to the virus in those who have been infected and their close contacts.

Here is an Altmetric ranking of March’s most popular papers in the natural sciences, published in the 82 high-quality journals tracked by the Nature Index.

1. “Extreme autotomy and whole-body regeneration in photosynthetic sea slugs”

Current Biology Some sea slugs from the genus Elysia can decapitate themselves and generate an entirely new body in a matter of weeks, according to this study led by Sayaka Mitoh, a PhD candidate at Nara Women’s University in Japan.

Mitoh and her supervisor Yusa Yoichi observed that these sea slugs could sever their heads at a “breakage plane” in the neck. The disembodied head would regenerate a new body, including a whole heart, within three weeks. The discarded body was left to decompose.

Only young sea slugs appeared to have this ability; slugs that were more than a year old died when their heads were severed.

Mitoh and Yoichi suggest that the sea slugs survive in their newly separated bodies by using the energy produced via photosynthesis occurring in cells they gained from eating algae. “[W]e propose that this unique characteristic may facilitate survival after autotomy and subsequent regeneration,” they write.

It’s not clear why certain species of sea slugs cut their entire bodies loose, but Mitoh and Yoichi suggest that it could be a way to shed parasites.

The study has been covered by more than 400 online news outlets to date. It’s reached an estimated audience on Twitter of more than 9 million.

2. “Exposure to SARS-CoV-2 generates T-cell memory in the absence of a detectable viral infection”

Nature Communications

Scientists from China and Australia teamed up to run this study on T-cell immunity against COVID-19, an important factor in recovery from the disease and a source of heightened immunity against re-infection.

The team collected samples from 90 COVID-19 patients between 48 and 86 days after the onset of the disease and 69 close contacts (family members or friends who had stayed with a SARS-CoV-2 infected individual within days of the disease onset), and compared them to samples collected from 63 healthy people at a blood donation centre in September 2019.

They found that most of the recovered COVID-19 patients had developed pools of memory T-cells that could mount an immune response to SARS-CoV-2, the virus that causes COVID-19. Their close contacts, who did not contract COVID-19, were also found to have had levels of SARS-CoV-2 specific memory T-cell immunity.

Only 3.17% of the healthy donor samples were found to contain virus-specific memory T-cells, likely developed in response to other coronaviruses that were in circulation before the COVID-19 pandemic.

“We ... demonstrate the size and quality of the memory T-cell pool of COVID-19 patients are larger and better than those of close contacts,” the team reports.

“However, the proliferation capacity, size and quality of T-cell responses in close contacts are readily distinguishable from healthy donors, suggesting close contacts are able to gain T-cell immunity against SARS-CoV-2 despite lacking a detectable infection.”

The study has been covered by only a couple of news sources so far, according to Altmetric, but has reached an estimated audience on Twitter more than 7 million.

3. “Lightning strikes as a major facilitator of prebiotic phosphorus reduction on early Earth”

Nature Communications

Bolts of lightning may have given early Earth one of its most important building blocks of life: the element phosphorus.

According to this study by Benjamin L. Hess from Yale University and Sandra Piazolo and Jason Harvey from the University of Leeds, UK, there is evidence to suggest that lightning strikes rivalled meteorites as important sources of prebiotic phosphorus when Earth was around 3.5 billion years old.

Phosphorus forms the backbone of DNA and RNA and other structural and functional elements in cells, but is often packaged up in minerals that are insoluble and unreactive, Hess told Phil Sansom at The Naked Scientists.

But there’s a phosphide mineral called schreibersite that readily reacts with water to free up the phosphorus inside. Not only is schreibersite commonly found in some types of meteorites, but it’s sometimes found in glasses formed by lightning strikes called fulgurites.

“When lightning hits the ground, it heats it to thousands of degrees Celsius and melts it immediately. And then it reforms [in fulgurites],” Hess told Sansom.

Based on calculations by Hess and his co-authors, “lightning could have been a significant source of prebiotic, reactive phosphorus” on early Earth, they report, and “could likewise provide a continual source of prebiotic reactive phosphorus independent of meteorite flux on other Earth-like planets, potentially facilitating the emergence of terrestrial life indefinitely”.

The paper has been covered by more than 300 news outlets. It’s reached an audience on Twitter of almost 1 million.

4. “Provision of High Meat Content Food and Object Play Reduce Predation of Wild Animals by Domestic Cats Felis catus

Current Biology

Rather than trying to impede the hunting of wildlife by house cats through confinement or the use of bells and bibs, non-invasive measures such as providing high-meat-protein food and regular object play could help reduce the tendency to hunt, according to this paper.

With Martina Cecchetti from the Environment and Sustainability Institute at the University of Exeter, UK as lead author, the study recorded decreases of 36% and 25%, respectively, in the numbers of animals captured and brought home by cats in households that implemented a high-meat-protein diet and 5–10 minutes of daily object play.

Cat bells were found to have no discernible effect, and while fitting Birdsbesafe collar covers (large, doughnut-shaped collars) reduced the numbers of birds captured and brought home by 42%, they had no discernible effect on the number of mammals preyed upon.

The study authors say cat owners might engage more with measures that not only benefit wildlife, but also their cats, than with more invasive strategies.

The paper has been covered by 250 online news outlets to date and has reached an estimated audience on Twitter of more than 1.5 million.

5. “Modelling human blastocysts by reprogramming fibroblasts into iBlastoids”


Led by an Australian team from Monash University in Melbourne, and involving researchers from the United States and Singapore, this study describes how they reprogrammed fibroblasts, or skin cells, into a three-dimensional cellular structure that is similar in physical and molecular composition to human blastocysts, the stage that the human embryo reaches roughly five to six days after fertilization.

Called iBlastoids, these structures could be used for in-vitro research into early human development and the causes of early miscarriage and infertility.

The study was conducted in the lab of Jose Polo from Monash University’s Biomedicine Discovery Institute and Australian Regenerative Medicine Institute, and involved the use of a technique called nuclear reprogramming, which allowed the researchers to change the cellular identity of human fibroblasts that organized into blastocyst-like structures when placed in a 3D ‘jelly’ scaffold.

The team says that while iBlastoids present a good option to researchers studying early human development, they are not completely identical to a blastocyst.

“For example, early blastocysts are enclosed within the zone pellucida, a membrane derived from the egg that interacts with sperm during the fertilization process and later disappears,” Polo explains. “As iBlastoids are derived from adult fibroblasts, they do not possess a zona pellucida.”

The paper has been mentioned by almost 300 news outlets to date and has reached an audience on Twitter of more than 700,000, according to Altmetric.