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How spi­ders “hear” with their legs

Spi­ders don’t have ears, but that doesn’t mean they can’t hear you com­ing. With eight eyes in ad­di­tion to eight legs, the crea­tures nav­i­gate mainly us­ing sight and touch, but they also have a limited au­di­tory abil­ity – pro­vided by sen­si­tive hairs on their legs, which pick up vi­bra­tions in solid ob­jects, such as leaves and web silk. Pre­vi­ously, it was as­sumed that air­borne sounds would only be de­tectable from a few cen­time­tres away; but re­searchers at Cor­nell Univer­sity have dis­cov­ered – by chance – that some spi­ders can “hear” sounds from across a room. The team had fit­ted elec­trodes to the poppy-seed-sized brains of North Amer­i­can jump­ing spi­ders, to record their brain ac­tiv­ity in re­sponse to vis­ual stim­uli. Then, dur­ing the ex­per­i­ment, a re­searcher ac­ci­den­tally caused his chair to squeak – and no­ticed that this, too, caused their neu­rons to fire. So the re­searchers then be­gan clap­ping while slowly back­ing away from the spi­ders – and found they seemed to reg­is­ter the sound from up to five me­tres away. Fur­ther ex­per­i­ments in a con­trolled cham­ber re­vealed the spi­ders were most sen­si­tive to low-fre­quency sounds, sug­gest­ing that the abil­ity may have evolved as a de­fence against their main preda­tor, the par­a­sitoid wasp, which emits a low sound with its wing­beats.

“Dark sky” puzzle solved

Most peo­ple, when they go out at night, take the dark sky, punc­tu­ated by twin­kling stars, for granted; yet as long ago as the 16th cen­tury, as­tronomers looked up and asked them­selves: why, if the uni­verse is static and in­fi­nite, isn’t the sky lit bright by its in­fi­nite num­ber of stars? This is the Ol­bers’s para­dox – named af­ter the Ger­man as­tronomer Hein­rich Ol­bers – and mod­ern sci­ence has come up with some an­swers: for in­stance, the uni­verse may ac­tu­ally be fi­nite, but ex­pand­ing faster and faster, a process that red­dens the colour of dis­tant stars. Ad­di­tion­ally, there were es­ti­mated to be only around one bil­lion tril­lion stars out there – a lot, of course, but not enough to blan­ket the sky. Now, how­ever, anal­y­sis of im­ages from Nasa’s Hub­ble Space Te­le­scope – which can see re­gions of space as far as 13.2 bil­lion light years away – has sug­gested that there are ac­tu­ally ten times as many stars as this. That is enough to light the sky, says the team at Not­ting­ham Univer­sity, but it re­mains dark be­cause much of their light is ab­sorbed by gi­ant hy­dro­gen clouds – which, iron­i­cally, is the ex­pla­na­tion that Ol­bers him­self came up with in 1823.

An end to in­fer­til­ity?

In an ex­tra­or­di­nary break­through in re­pro­duc­tive bi­ol­ogy, sci­en­tists have turned mouse skin cells into egg cells in the lab – and, for the first time, used them to breed mice pups. The team, in Ja­pan, says that if they can ap­ply the same tech­nique to hu­mans, it would es­sen­tially “cure” in­fer­til­ity, and even pave the way for two men to par­ent a child with­out the use of an egg donor. The re­searchers be­gan by tak­ing cells from mice tails and – us­ing a tech­nique de­vel­oped in 2007 – coaxed them into be­com­ing pluripo­tent stem cells that can di­vide in­fin­itely and have the po­ten­tial to de­velop into any tis­sue. Then, they re­pro­grammed these as sex cells, fol­low­ing a method de­vel­oped in 2012. Their break­through was in ma­tur­ing those cells into fer­tile eggs, with­out hav­ing to im­plant them back into an ovary. In­stead, they took ovar­ian cells from a mouse, and used these to cre­ate an ovary-like en­vi­ron­ment that tricked the cells into de­vel­op­ing into eggs. These were then fer­tilised and im­planted in the wombs of fe­male mice. How­ever, of the 4,048 eggs pro­duced, only eight led to live births. Im­prov­ing this fail­ure rate is one of the many hur­dles that will have to be over­come be­fore the tech­nique can be tested on hu­mans.

Cannabis and bone health

Long-term cannabis users break their bones more fre­quently than non-users, re­ports The Times. How­ever, it isn’t clear whether this is be­cause the drug weak­ens peo­ple’s skeletons – or sim­ply be­cause when stoned, peo­ple tend to fall over more. A team at Ed­in­burgh Univer­sity com­pared the frac­ture rates of heavy users (who’d smoked the drug 5,000 times or more), mod­er­ate users, and a con­trol group of cig­a­rette smok­ers, and found that the heavy users had suf­fered twice as many frac­tures as the con­trol group.

Jump­ing spi­ders can hear sounds across a room

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