Artist's impression of a mammal-like creature breathing out hot air.

The ancestors of modern mammals developed the ability to regulate their own body temperatures, which might have been useful in cool climates.Credit: Luzia Soares

Ear fossils hint at origin of ‘warm blood’ in mammals

The reptile-like ancestors of mammals evolved to be warm-blooded — but the timing of this transition is hotly contested. Now scientists have used fossilized inner ear canals to suggest that the adaptation occurred around 230 million to 200 million years ago.

Warm-blooded animals, or endotherms, can maintain a constant high body temperature because of their fast metabolisms. But it is difficult to measure these traits in fossils. Ricardo Araújo, a palaeontologist at the University of Lisbon, and his colleagues propose that the shape and size of the bony canals of the inner ear could be used as a proxy for body temperature (R. Araújo et al. Nature; 2022). The movement of fluid through the canals helps the body to monitor head position and motion. This fluid becomes less viscous as body temperature increases; the team hypothesized that as this happened and the animals became more active, the shape of the ear canals would have evolved.

When they analysed the ear canals of 56 extinct synapsids — the reptile-like ancestors of mammals — the authors found that the shape of the canals had changed abruptly in the Late Triassic period. They suggest that this is when synapsids became warm-blooded.

Molecular motor is DNA origami milestone

Physicists have built a molecular-scale motor entirely from DNA strands, and used it to store energy by winding up a DNA ‘spring’. It is not the first DNA nanomotor, but it’s “certainly the first one to actually perform measurable mechanical work”, says Hendrik Dietz, a biophysicist at the Technical University of Munich in Germany whose team reported the results on 20 July (A.-K. Pumm et al. Nature 607, 492–498; 2022).

The tiny machine gains energy from Brownian motion — the constant, random movement of molecules in a medium. It turns like the ratchet wheel in a clock, winding a string of DNA like a spiral spring.

The technique used to make the motor adds to a growing list of ‘DNA origami’ tricks that are being used to build structures on the molecular scale. Loops of single-stranded DNA from a bacteriophage virus are mixed together in a solution with short strands of synthetic DNA; these are made to match the nucleobase sequences of specific sites in the viral genome. The short pieces bind to the long strands and force them to fold into the desired shape. Since this technique was first demonstrated in 2006 (P. W. K. Rothemund Nature 440, 297–302; 2006), researchers have built DNA origamis of increasing complexity. The approach could find applications in fields such as chemical synthesis and drug delivery.

Researchers watch another researcher carrying out an experiment under a microscope in the lab

Dozens of research teams at RIKEN’s network of basic research laboratories will be closed down early next year.Credit: Kyodo News Stills/Getty

‘I feel disposable’: thousands of scientists’ jobs at risk in Japan

Thousands of researchers and university staff members in Japan are at risk of losing their jobs next year because of apparent loopholes in employment laws implemented a decade ago. Researchers are alarmed at the scale of the potential job losses, and say the cuts would have a devastating effect on research capacity.

The laws, introduced in 2013 and 2014, were designed to give researchers on fixed-term contracts some long-term job security, by putting a ten-year time limit on such agreements. After that time, employees have the right, in principle, to request a permanent position. Next April marks a decade since the first of the rules came in. But some researchers on temporary contracts are finding that their institutions are terminating their employment — or asking them to resign — just before they are eligible for permanent jobs.

There are roughly 3,100 researchers on fixed‑term contracts at dozens of national universities and research centres who will have been employed for 10 years by the end of March, according to Japan’s Ministry of Education, Culture, Sports, Science and Technology. Some of those people might be made permanent employees, but many will lose their jobs, say researchers.

They warn that if the potential job losses go ahead, the effect could be devastating for Japanese science. Enrolment in doctoral programmes has been declining since 2003. That, combined with researchers losing their jobs because of the ten-year limit on fixed-term employment, will create a major problem for the country’s ability to develop a pipeline of researchers doing basic science, says Yasuyuki Kanai, chair of the executive committee of the labour union at RIKEN, a large, government-funded network of basic-research laboratories, which is headquartered in Wako near Tokyo. “If the ten-year employment termination is not rescinded and employment is not stabilized, it will definitely lead to a decline in Japan’s scientific research capacity in the long run,” says Kanai.

The science and education ministry told Nature that employers should not force staff out to avoid hiring them permanently.