Multi-task­ing mu­cus

Focus-Science and Technology - - REPLY -

The sil­very slime or mu­cus se­creted by slugs and snails (July, p84) has many more ad­van­tages, and some­times dis­ad­van­tages, than just help­ing the mol­luscs to move around eas­ily.

In the marine world, it has been found that some snails add nu­tri­ents – par­tic­u­larly ni­tro­gen – to their slime as a fer­tiliser that stim­u­lates the growth of the al­gal spores which get stuck to the mu­cus, thus en­rich­ing the habi­tat for fu­ture graz­ing.

Slime can also be used for nav­i­ga­tion, a prime ex­am­ple be­ing limpets, who use their own mu­cus trails to find their way back to their home spot on the rocks after feed­ing. They then seal them­selves down with mu­cus to com­bat des­ic­ca­tion as the tide re­cedes. Ter­res­trial snails can also seal them­selves into their shells dur­ing hot, dry spells.

The slime also con­tains some pheromones, there­fore al­low­ing oth­ers of the same species to find a mate (or an ag­gre­ga­tion of oth­ers for mass mat­ing, as with sea hares and other sea slugs). The crea­tures seem to be able to sense which di­rec­tion the trail has been laid in. Un­for­tu­nately, though, car­niv­o­rous snails can also fol­low these trails to find their prey, while oth­ers can add tox­ins to ward off preda­tors or se­crete toxic mu­cus which makes them dis­taste­ful.

And it’s not just other mol­luscs that have to be wary of mu­cus trails. Some years ago marine sci­en­tists from Ply­mouth noted that bar­na­cle lar­vae avoided set­tling on dog whelk trails, a vo­ra­cious preda­tor of bar­na­cles, or near to some species of limpets which have a habit of bull­doz­ing the set­tling bar­na­cles from the sur­face of rocks.

Paul Big­gin, Hert­ford

Dive free

Fur­ther to your ques­tion, ‘Can marine an­i­mals get the bends?’ (Sum­mer, p82), all marine mam­mals are free­d­iv­ing, and while car­bon diox­ide may build up over time, the ni­tro­gen they took with them is all they have as op­posed to breath­ing in scuba div­ing. Scuba div­ing and its var­i­ous forms push ni­tro­gen into the blood­stream, free­d­iv­ing does not. Hence, there’s lit­tle chance for ‘the bends’ with free­d­iv­ing. Henry Depew,

Tallahassee, Florida

The Mal­tese mo­lar

Your fea­ture on Ne­an­derthals (Sum­mer, p64) is of par­tic­u­lar in­ter­est to us in Malta. The last Ne­an­derthal to be iden­ti­fied was in 2016, when two lead­ing phys­i­cal an­thro­pol­o­gists, Prof Shara E Bai­ley and Aida Gomez-Robles, con­firmed a mo­lar that was dis­cov­ered in the Du­lam Cave in Malta in 1917 as Ne­an­derthal. This find was unique in that the mi­croanatom­i­cal fea­tures on this mo­lar sug­gested a blend of Ne­an­derthal with anatom­i­cally mod­ern hu­mans of the Late Palae­olithic. Prof Chris Stringer at London’s Nat­u­ral His­tory Mu­seum ex­tended the re­search on the mo­lar and in­volved Prof Svante Pääbo in the dis­cov­ery. Pääbo, a Swedish bi­ol­o­gist, is one of the founders of palaeo­ge­net­ics and has worked ex­ten­sively on the Ne­an­derthal genome. He ar­ranged

for DNA stud­ies of the tooth at the Max Planck In­sti­tute for Evo­lu­tion­ary An­thro­pol­ogy in Leipzig, in or­der to set­tle the is­sue of whether hu­mans on Malta had mated with Ne­an­derthals. But at that stage the lo­cal ar­chae­o­log­i­cal es­tab­lish­ment opted to take mat­ters into their own hands, and the out­come is still be­ing awaited. An­ton Mif­sud, MD, DSc, DCH (Lond)

Flatly speak­ing

Your com­par­i­son (Septem­ber, p58) of those who do not be­lieve the of­fi­cial ac­count of (eg) Pres­i­dent Kennedy’s as­sas­si­na­tion with Flat Earthers and neo-Nazis dis­cred­its you. In the case of the Kennedy as­sas­si­na­tion, the United States House Se­lect Com­mit­tee on As­sas­si­na­tions con­cluded in 1979 – in con­trast to the con­clu­sions of the War­ren Com­mis­sion – that Kennedy was “prob­a­bly as­sas­si­nated as a re­sult of a con­spir­acy,” which seems like an un­der­state­ment of the blind­ingly ob­vi­ous. That the co­op­er­a­tion and si­lence of what seems likely to have been a large num­ber of con­spir­a­tors could be achieved lends cred­i­bil­ity to other, more re­cent, al­leged cover-ups by the lead­ers of west­ern democracies. Martin Keat­ing, Falkirk

Apollo omis­sion

I read your ar­ti­cle cel­e­brat­ing 60 years of NASA (Au­gust, p56), and am as­ton­ished that you left out one of the most im­por­tant mis­sions NASA ever un­der­took: Apollo 8.

The Apollo 8 mis­sion achieved a num­ber of sig­nif­i­cant firsts – the first manned flight of the Saturn V rocket, the first mis­sion to send hu­mans be­yond the pull of Earth’s grav­ity – and pro­duced the stun­ning Earthrise pho­to­graph taken by as­tro­naut Bill An­ders. How could you leave this out? Steve Jones, Bed­ford

Oops

On p22 of our Septem­ber is­sue, we said that pan­cre­atic can­cer pa­tients who re­ceived treat­ment with CBD lived up to three times longer. This was in­cor­rect as the study in­volved mice rather than hu­man pa­tients.

Apolo­gies, puz­zlers. In our Septem­ber crossword (p96) there were two clues num­bered as 21 down.

Why don’t marine an­i­mals get the bends? Be­cause they’re not us­ing scuba gear, says Henry Depew

JFK – there was def­i­nitely some kind of con­spir­acy, ar­gues Martin Keat­ing

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