Nature：科学家发现哺乳动物在水下可以利用嗅觉
BY：Maha 2024-07-08 00:30:17 102 ℃
CourtesyofKennethCataniaKennethCatania
Forsometime,KennethCataniahadnoticedthatthestar-nosedmoleshestudiesblowalotofbubblesastheyswimaroundunderwater.Butitwasn'tuntilrecentlythathereallypaidattentiontothisbehaviorand,whenhedid,hediscoveredthatthemoleswereblowingbubblesinordertosmellunderwaterobjects.
"Thiscameasatotalsurprisebecausethecommonwisdomisthatmammalscan'tsmellunderwater,'saystheassistantprofessorofbiology."Whenmammalsadapttolivinginwater,theirsenseofsmellusuallydegenerates.Theprimaryexampleofthisarethecetaceans―whalesanddolphins―manyofwhichhavelosttheirsenseofsmell."
Catania,whoearlierthisyearwona$500,000"geniusgrant"fromtheJohnD.andCatherineT.MacArthurFoundation,devisedaseriesofexperimentstodeterminewhetherthestar-nosedmoleandanothersmall,semi-aquaticmammal,thewatershrew,cansmellobjectsunderwaterandusedahigh-speedcameratodiscoverhowtheydoit.TheresultsarereportedintheDec.21,2006issueofthesciencejournalNature.
Oneofthefirstthingstheresearchernoticedwasthatthemoleswereblowingbubblesoutoftheirnostrilsandthensuckingthemrightbackin."Theyoftenloosepartofthebubbles,butmostoftheairgoesrightbackintotheirnose,"hesays.
Cataniaalsodeterminedthatthemoleswereexhalingandinhalingthesebubblesrapidly,betweenfiveand10timespersecond.Thatisaboutthesamerateasthesniffingbehaviorofcomparablysizedlandmammals,likeratsandmice."Ratsandmicedon'tsniffthewaywedo,"hesays."Theypushair'out-inout-in'inafashionstrikinglysimilartowhatthestar-nosedmoleisdoing,exceptthatitisdoingitunderwater!"
Theresearchermountedahigh-speedvideocamerasothatitpointedupthroughthebottomofaglasstank.Thenhestuckvariousobjectsonthebottomofthetank―piecesofearthworm,smallfish,insectcuticleandblobsofwaxandsilicon―andobservedthemoles'behavior.Hesawthat,whenthemolesapproachedoneofthesetargets,theywouldblowbubblesthatcameintocontactwiththetarget'ssurfaceandthenweresuckedbackintothenostrils.
"Becausetheolfactorynervesinthenosearecoveredwithmucous,odorantmoleculesareallwatersoluble,"saysCatania."So,whenthesebubblescomeintocontactwithanobject,itisalmostinevitablethatodorantmoleculeswillmixwiththeairandbedrawnintothenosewhenthebubbleisinhaled."
Justbecausethemolesaregettingwhiffsofinterestingodorsunderwaterdoesn'tnecessarilymeanthattheyareactuallysmellingthem.SoCataniadevisedsomeadditionaltests.
Oneofthecomplicatingfactorswasthestar-nosedmole'sunusualnose,whichisringedbyastar-shapedsetoffleshyappendages.Itusesitsstarlikeasuper-sensitivesetoffingerstoidentifyobjectsitencounterswhileburrowingandswimming.So,atthesametimeitissniffingatanobjectitisalsofingeringitwithitsstar.
Todetermineifthemolecanidentifyedibleobjectsbysniffingalone,Cataniacreatedunderwaterscenttrailsleadingtofoodandrecordedhowwellthemoles'couldfollowthem.Tokeepthemolesfromusingtheirtactilestar,heputagrid-workbetweentheanimalsandthescenttrails.Theopeningsinthegridweretoosmallforthestarappendagestosqueezethroughbutlargeenoughsotheairbubblescanpasswithoutdifficulty.
Thesetrialsdemonstratedthatthemolescouldfollowthescenttrailbysniffingalone（withoutthetactilestar）.Fivemolesweretestedonearthwormscenttrailsandfollowedthetrailtoitsrewardwithaccuraciesrangingfrom75percentto100percentaccuracy.Twomolesweretestedwithfishscenttrailsandfollowedthemwith85percentand100percentaccuracy.
Whenthegridwasreplacedwithascreenwithopeningstoosmallfortheairbubblestopassthrough,however,themoles'performancedroppeddowntothelevelofchance―thesameastheirperformancewithno-scenttrails.
Inordertoseeifthiscapabilitywaslimitedtothestar-nosedmoleorifothersmallsemi-aquaticmammalsalsohaveit,Cataniacapturedsomewatershrewsandbegantestingthem.Hefoundthattheyalsoexhibitthisunderwatersniffingbehaviorandcanuseittofollowunderwaterscenttrails.
"Now,thequestionis,'Whatothersemi-aquaticmammalsdothis?'"Cataniasays."Doanimalslikeottersandsealsdoanythingsimilar?Oristhereasizelimitanditonlyworksforsmallermammals?"
Hehopesthatpublicationofhispaperwillencourageresearcherswhoarestudyingallkindsofsemi-aquaticanimalstotakeacloserlookathowtheyar eusingtheirnosesunderwater.
TheresearchwasfundedbyaFacultyEarlyCareerDevelopment（CAREER）awardfromtheNationalScienceFoundation.
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