Readers ask about extinction boundaries, crater shapes and more

Mirror, mirror

Clay models of dim and shiny beetles have shown that the mirrored exterior of Christmas beetles cannot serve as a form of camouflage from predators, Susan Milius reported in «Scientists are suffering from the theory of brilliant camouflage»(SN: 09.04.22, p. 4).

Perhaps clay models simply could not reproduce all the possible ways in which the shiny bodies of beetles affect the light and protect insects, reader Ron Kern suggested.

However, clay models did not mimic all the possible lighting effects created by Christmas beetles, Milius I say. But that was not the purpose of the experiment. Think of the study as a kind of dissection, considering only one possible easy trick at a time, she says. The results show that shine in itself is not a deterrent to predators. Further tests may investigate whether other aspects of the mirror surface of the beetle may benefit these spectacular insects, Milius I say.

Crater shapes

The impact that formed the Hiawatha Crater in Greenland occurred about 58 million years ago. Carolyn Grammling reported in «The shock crater of Greenland is surprisingly old»(SN: 09.04.22, p. 5).

Reader Bari Malecki asked why most impact craters are round, given that space rocks can hit at different angles.

Most craters are round due to the blast, says the deputy news editor Christopher Crockett. When space rocks crash into rocky planets and satellites at high speed, a huge amount of energy is transferred in a short period of time. At most angles, this process forms typically round craters that we see, scientists said in 2013. Journal of Geophysical Research: Planets. “The effect is similar to planting an explosive on the site and allowing it to explode,” Crockett I say.

Although they are rare, elliptical craters are found in the solar system, and the angle of impact plays a role. Research has shown that the angle at which a crater becomes elliptical rather than round depends on the size of the space rock, the impact velocity and the type of material at the impact site.

Resurrection checkpoint

Scientists have reconstructed the genome of an extinct rat from Christmas Island, comparing it to the genome of a living relative. But some key DNA remains a mystery, Anna Gibbs reported in «The rat discovers the limits of extinction»(SN: 09.04.22, p. 12).

Reader Tim Cliff wondered if it was possible to reconstruct the complete genome given enough DNA samples from different samples of extinct species.

The point is not that DNA is missing, but that scientists cannot understand all the genetic sequences they have, he says. Tom Gilbert, an evolutionary biologist from the University of Copenhagen. Some genes in the genome of Christmas Island rats are so divergent that they do not resemble the reference genome. If we can’t identify the gene, we can’t re-create it in the reference genome to eliminate it, Gilbert I say.

Deciphering brain waves

Researchers are studying the emotions of horses, octopuses and other creatures to understand how animals feel about the world. Ala Katznelson reported in «What do animals feel?»(SN: 09.04.22, p. 16).

In one study, horses that spent more time alone had greater gamma-wave activity than horses that grazed freely with the herd. Katznelson reported. In humans, high levels of such brainwave activity have been linked to anxiety and stress. Reader Barbara Alan thought the opposite: low levels of brain gamma waves are associated with stress and anxiety in humans.

Scientists are still figuring out how brain waves in humans relate to different mental states, Katznelson I say. The study of brain waves and the interpretation of these studies are complex, and the results in this area differ. In her report, researchers who have studied horses point to evidence linking anxiety and stress to increased gamma waves in humans, she says. But other groups have found conflicting results, complicating the picture.

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