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What bats have to say about speech and language

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What bats have to say about speech and language
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Psychonomic Bulletin & Review
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Vernes, Sonja C.
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Understanding the biological foundations of language is vital to gaining insight into how the capacity for language may have evolved in humans. Animal models can be exploited to learn about the biological underpinnings of shared human traits, and although no other animals display speech or language, a range of behaviors found throughout the animal kingdom are relevant to speech and spoken language. To date, such investigations have been dominated by studies of our closest primate relatives searching for shared traits, or more distantly related species that are sophisticated vocal communicators, like songbirds. Herein I make the case for turning our attention to the Chiropterans, to shed new light on the biological encoding and evolution of human language-relevant traits. Bats employ complex vocalizations to facilitate navigation as well as social interactions, and are exquisitely tuned to acoustic information. Furthermore, bats display behaviors such as vocal learning and vocal turn-taking that are directly pertinent for human spoken language. Emerging technologies are now allowing the study of bat vocal communication, from the behavioral to the neurobiological and molecular level. Although it is clear that no single animal model can reflect the complexity of human language, by comparing such findings across diverse species we can identify the shared biological mechanisms likely to have influenced the evolution of human language.

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WhatbatshavetosayaboutspeechandlanguageSonjaC.Vernes1,2Publishedonline:1July2016 # TheAuthor(s)2016.ThisarticleispublishedwithopenaccessatSpringerlink.comAbstract Understandingthebiologicalfoundationsoflanguageisvitaltogaininginsightintohowthecapacityfor languagemayhaveevolvedinhumans.Animalmodelscan beexploitedtolearnaboutthebiologicalunderpinningsof sharedhumantraits,andalthoughnootheranimalsdisplay speechorlanguage,arangeofbehaviorsfoundthroughout theanimalkingdomarerelevanttospeechandspokenlanguage.Todate,suchinvestigationshavebeendominatedby studiesofourclosestprimaterelativessearchingforshared traits,ormoredistantlyrelatedspeciesthataresophisticated vocalcommunicators,likesongbirds.HereinImakethecase forturningourattentiontotheChiropterans,toshednewlight onthebiologicalencodingandevolutionofhumanlanguagerelevanttraits.Batsemploycomplexvocalizationstofacilitate navigationaswellassocialinteractions,andareexquisitely tunedtoacousticinformation.Furthermore,batsdisplaybehaviorssuchasvocallearningandvocalturn-takingthatare directlypertinentforhumanspokenlanguage.Emergingtechnologiesarenowallowingthestudyofbatvocalcommunication,fromthebehavioraltotheneurobiologicalandmolecular level.Althoughitisclearthatnosingleanimalmodelcan reflectthecomplexityofhumanlanguage,bycomparingsuch findingsacrossdiversespecieswecanidentifytheshared biologicalmechanismslikelytohaveinfluencedtheevolution ofhumanlanguage. Keywords Bats Vocallearning Turn-taking Language Languageevolution SpeechAnimalmodelsrelevanttospeechandlanguageThecomparativeapproach,investigatingsimilartraitsacross diversespecies,hasbeenadrivingforceinunderstandingthe genetics,physiology,andevolutionofcomplextraits.The studyofsuchtraitsinexperimentalanimalmodelshasshed lightonhuman-relevantprocessesinvolvedinbothnormal developmentanddiseasestates.Despitetheirpower,applying theseapproachestothestudyofspokenlanguagepresents particulardifficulties,giventhat(a)spokenlanguagedoes notleavedirectevidenceinthefossilrecord,makingcomparisonstoourextinctancestorschallenging,and(b)humansare theonlyextantspecieswiththistrait. Althoughlanguageisnotfoundinotheranimals,some aspectsofsocialandvocalanimalcommunicationare likelytoinformusabouthowthistraitevolved(Fitch, Huber,&Bugnyar, 2010).Vocallearningisanessential componentofspokenlanguage,andsongbirdshavebeen thedominantmodelusedtostudythistrait,duetotheir well-definedlearningparadigm,sexualdimorphismof theirsong,andtheabilitytobreedtheseanimalsincaptivity(Condro&White, 2014 ).Songbirdshavebeena successstory,revealingmuchaboutthewiringofspecific circuits(e.g.,theanteriorforebrainpathway;Doupe, Solis,Kimpo,&Boettiger, 2004)andgeneticcomponents(e.g., FoxP2;Haesleretal., 2007)involvedinthis complexbehavior.Howeversimilarlevelsofsuccess havenotbeenachievedoutsideavianmodelsystems, andthusexactlyhowthesemechanismstranslatetothe mammalianbrainstilldemandsinvestigation. Conversely,primatestudieshaverevealedcomplex SonjaC.Vernes sonja.vernes@mpi.nl1MaxPlanckInstituteforPsycholinguistics, Nijmegen,TheNetherlands2DondersInstituteforBrain,CognitionandBehavior, Nijmegen,TheNetherlands PsychonBullRev(2017)24:111 – 117 DOI10.3758/s13423-016-1060-3

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nonverbalcommunicationabilities(e.g.,communication viasignlanguageorvisualreferentialsystems),butdespiteintensivetraining,primateshaveneverbeenableto acquirelanguageabilitiesgreaterthanthoseofahuman toddler,orindeedanycapacityforspeech(Fitch, 2000). Givenspokenlanguage ’ sexclusivitytohumans,nosingle animalmodelisgoingtoprovidealloftheanswersregarding howitisencodedorhowitevolved.Rather,weneedtoseek cluesfromarangeofphylogeneticallydiversespecieswith language-relevanttraits,explo itingbothobservationalstudies and,wherepossible,animalmodelsamenabletolaboratorystudies.Onlybyintegratingthisinformationacrossspecieswillwe beabletobuildapictureoftheessentialcomponentsthatwould allowanorganismtodevelopandemployspokenlanguage.ThepromiseofchiropteraOneorderofanimalsthatareparticularlypromisingforthe studyoflanguage-relevanttraitsisChiroptera(bats).Bats arose~64millionyearsagoandarethesecond-largestgroup ofmammals(behindrodents),with18familiesrepresenting extensiveevolutionaryandfunctionaldiversity(Teelingetal., 2005 ).Asmammals,batssharebrainstructuressuchasasixlayeredcortexandhippocampuswithhumansandothermammals,whichisaconsiderableadvantagewheninterrogating therolesoftheseregions(andtheassociatedcircuitry)in complex,spoken-language-relevanttasks. Batshavedevelopedsophisticatedvocalsystemsfornavigationandcommunication,andmanyspeciesrelyonecholocationtonavigatetheirenvironmentandhuntprey.Most echolocatingbatsproducecallsfromthelarynx(seeAu& Suthers, 2014 ,foracomprehensivereviewofbatlaryngeal controlandbiosonarproduction)andusethereturningechoes todetectthestructureoftheirenvironment.Thismeansthat echolocatingbatsarehighlyskilledatproducingprecise,rapid vocalizations,andtheirauditorysystemsandneurobiology areexquisitelytunedtoacousticinformation — importantfactorsalsorequiredforthedevelopmentofcomplexvocalcommunication.Echolocationhasbeenwell-studiedinbats,and thusthefunctionalityofdifferentcalltypes(Jones&Teeling, 2006 ),neurobiologicalmechanisms(Moss&Sinha, 2003 ), andgeneticevolution(Parkeretal., 2013 )arebecomingwell understood(Jones,Teeling,&Rossiter, 2013 ). Vocalizations(sonicand/orultrasonic)arealsoheavily employedbybatstofacilitatesocialcommunication(Pfalzer &Kusch, 2003 ).Mostbatsarehighlysocial,livingingroups (oftenfission – fusiongroups)thatmayrangefromasmallroost ofafewanimalstolargecolonieswithmillionsofinhabitants. Socialcommunicationintheseenvironmentshasbeenfound inthecontextofallogrooming,mother – pupinteractions,group contactcalls,foragingcalls,mateattraction,andterritorialdefense(Behr&vonHelversen, 2004;Kerth, 2008 ;Pfalzer& Kusch, 2003;Wilkinson,Carter,Bohn,&Adams, 2016 ). Howeverthediversityofbatspeciesandtheirfrequentlyinaccessiblehabitats,ultrasonicformofsomevocalizations,and abundanceofcalltypes,meanthatmuchisstilltobeunderstoodabouttherangeandfunctionofsocialvocalizations. Ipositthatgiventheircomplexvocalizations,biological specificationforvocalcontrol/auditoryprocessing,anddiversefamilytree,batsrepresentahighlyappealingyetcurrentlyunderstudiedsystemtoinvestigatethebiologicalbasis andevolutionofspokenlanguageinamammaliansystem. HereinIdiscusstwofacetsofvocalcommunicationthathave relevancetohumanspokenlanguageandforwhichbatsshow greatpromise:vocallearningandvocalturn-taking.LearnedvocalcommunicationVocallearningcanbeclassifiedintovocalproductionlearning (sensory – motorlearning)andcontextuallearning(theusage orcomprehensionofvocalizations;Janik&Slater, 2000 ). Vocalproductionlearning(VPL)istheabilitytomodifyvocalizationsinresponsetointeractionswithconspecifics,and allowshumaninfantstoadvancefromproducingincoherent babblingtoameaningfulvocallexicon.VPLisacentralcomponentneededfortheevolutionofhumanspeechandinvolvestheintegrationofinformationacrossmodalities,includingauditoryperception,memory,andmotorproduction. Tolearnavocalization,relevantsoundsproducedbyconspecificsmustberecognizedandthisvocaltemplatemustbe remembered.Thenamotorprogramattemptingtomimic thesesound(s)mustbeplannedandenacted.Theoutputof thismotorprogrammustbecomparedagainstthetemplateto determinematch/mismatch,an difnecessary,adjustments mustbemadeuntiltheoutputmatchesthetemplate.Social interactionsbetweenconspecificsmayalsoreinforcetheselectionoftheappropriateoutputs(West&King, 1988 ). ThereisstrongevidenceforVPLinonlyahandfulof nonhumananimals,includingsomebirds(songbirds,parrots, andhummingbirds),pinnipeds(seals),cetaceans(whales),elephants,andsomebats(Janik&Slater, 1997 ;Knrnschild, 2014 ;Petkov&Jarvis, 2012 ).Howeverithasbeenhypothesizedthatthelackofevidenceinalargernumberofspecies maybeduetoinsufficientstudy,andindeed,morewideranginginvestigationsmaypointtoacontinuumofvocallearningabilitiesratherthanasimpleclassificationofanimals asvocallearnersversusnonlearners(Petkov&Jarvis, 2012 ). Batspresentahighlypromisingsystemthroughwhichto studybehavioralandbiologicalaspectsofvocallearning. Despitetheirextensivespeciationanddiversevocalandecholocationmechanisms(e.g.,constant-frequencyvs.frequencymodulatedcalls),batsfromacrosstheChiropteranfamilytree displayevidenceforvocallearning(Knrnschild, 2014 ). 112 PsychonBullRev(2017)24:111 – 117

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Vocallearninginphyllostomidae — open-endedlearning DirectexperimentalevidenceforVPLinbatsfirstcamefrom socialcommunicationcallsproducedbythepalespear-nosed bat( Phyllostomusdiscolor )inthePhyllostomidaefamily. P.discolor pupsemitisolationcallsinresponseto frequency-modulated(FM)maternal B directive^ callsthat areusedformother – pupidentification/reunion(Rother& Schmidt, 1985 ).Naturallyrearedpupsmodifytheirisolation callstoadopttheFMpropertiesoftheirmother ’ scall(Esser& Schmidt, 1989 ),andhand-rearedpupsadapttotheFMpropertiesofdigitaldirectivecalls,demonstratingtheirabilityto learnfromaconspecifictemplate(Esser, 1994 ).Itisnotclear whether P.discolor batshaveacriticalperiod(likezebrafinch songbirds)orareabletocontinuelearningnewvocalizations intoadulthood(likeparrots,whales,ordolphins).However Phyllostomushastatus ,oneofthespeciesmostcloselyrelated to P.discolor ,isanopen-endedlearner,abletolearnvocalizationsintoadulthood. P.hastatus batsformstablesocial groupsofunrelatedfemalesthatproduceasignaturegroup contactcall,knownasa screechcall (Boughman, 1998). Whenanimalsjoinanewgroup,boththeexisting B residents ^ andnewmembers(bothjuvenileandadult)adapttheircall characteristicstoestablishanewgroupsignaturecall (Boughman, 1998 ).Since P.hastatus isanopen-endedlearner,itislikelythat P.discolor batswillalsobeabletocontinue learningvocalizationsintoadulthood,butcontrolledexperimentalparadigmsdirectlyprovingthiswillbeessential. Vocallearninginemballonuridae — babblingandlearned song Thegreatersac-wingedbat( Saccopteryxbilineata )in theEmballonuridaefamilyproducesFMecholocationcalls andarichrepertoireofsocialcommunicationcalls,includingisolationcalls,courtshipsongs,andterritorialsongs (Behr&vonHelversen, 2004).Theirsocialvocalizations havebeenfoundtocontainindividualandgroupsignature information,andtheirecholocationcallscontainindividual andsexsignatures(Eckenweber&Knrnschild, 2013; Knrnschild,Jung,Nagy,Metz,&Kalko, 2012; Knrnschild,Nagy,Metz,Mayer,&vonHelversen, 2012). S.bilineata juvenileslearnterritorialsongs(containingindividualandgroupsignatures)thatthemalesuseto defendtheirhomeroostagainstinvasionfromadultmales (Eckenweber&Knrnschild, 2013;Knrnschild,Nagy, Metz,Mayer,&vonHelversen, 2010).Despitethissexual dimorphism,bothsexesproduceallpossibleadultcall typesaspups,andduringontogenythesecallsareflexibly practicedinafashionreminiscentofsongbirdvocallearningandhumaninfantbabbling(Knrnschild,Behr,&von Helversen, 2006;Knrnschildetal., 2010 ).Thisspecies offersexcitingopportun itiesforthestudyofspoken language-relevanttraits,giventhepresenceofbothlearned vocalizationsandbabblingbehavior. Vocallearninginpteropodidae — juvenilevocaldevelopment TheEgyptianfruitbat( Rousettusaegyptiacus )isalarge OldWorldmegabatfromthefam ilyPteropodidae.OldWorld fruitbatsdonotuselaryngealecholocation;instead,genus Rousettus havedevelopedamethodforecholocationthatinvolvesproducingtongueclicks(Yovel,Geva-Sagiv,& Ulanovsky, 2011).Recently, R.aegyptiacus providedevidence ofvocallearningduringbatjuveniledevelopment.Prat,Taub, andYovel( 2015 )undertookthedauntingtaskofdocumenting thecomplexvocalontogenyof R.aegyptiacus overa9-month period,producingadatasetof>1millioncalls(Pratetal., 2015 ).Byobservinganimalsraisedinthepresenceofadults ascomparedtoisolatedanimalst hatonlyinteractedwithother isolatejuveniles,theywereable todemonstratethatexposureto adultvocalizationsinfluencedthedevelopmentofthe R.aegyptiacus vocalrepertoire(Pratetal., 2015 ).Isolateanimalsmaintainedasignificantly differentcallfromthoseofnormallyrearedadults,a ndmoreover,theycouldbeinducedto shiftthefrequencyoftheirvocalizationsbyexposuretoplaybackofcallsrarelymadebynormaladult R.aegyptiacus (Prat etal., 2015 ).Thisworksuggeststhatsomeformofvocallearning(eitherproductionorcontextual)isrequiredforthenormal developmentof R.aegyptiacus andillustratestheexperimental promiseofbatsforcharacterizingvocal-learningbehavior.In thefuture,itwillbeofgreatinteresttoextendtheseparadigms toshowwhetherthesebatsarecapableoflearningnovelsounds nevernormallyproducedbyadultbats. Insummary,evidenceisaccumulatingthatbatsfrommultiplespeciesarecapableofvocallearning.Infact,thespecies forwhichvocallearninghasbeendemonstratedarefound spreadthroughouttheChiropteranphylogenetictree,with promisingorconfirmedvocallearnersidentifiedinaround halfofthe18familiesofbats,includingacrossthetwomajor batsuborders,YinpterochiropteraandYangochiroptera (Knrnschild, 2014 ;Pratetal., 2015 ).Thissuggeststhatwith furtherstudieswemayfindthatvocallearningisageneral,or atleasthighlyprevalent,featureofbatbehavior,providinga richframeworkinwhichtoinvestigatethisspoken-languagerelevanttrait.Giventhatsomevocal-learningbatspeciescan behousedinlaboratorycolonies(e.g., P.discolor and R.aegyptiacus ),thisaffordsnewopportunitiestodirectlyinvestigatetheneurobiologicalandgeneticmodelsproposed fromavianstudies(Bouchard&Brainard, 2013 ;Brainard& Doupe, 2013 ;Scharff&Petri, 2011 ;White, 2010 )inamammalianbrain.Suchcomparativestudieswillbeanimportant stepinfindingcommonmechanismsunderlyingtheevolution ofvocallearninginhumans.TakingturnsduringvocalcommunicationHumanlanguageisexceedinglydiverse,andfew(hotlydebated)universalpropertieshavebeenproposedthatareshared PsychonBullRev(2017)24:111 – 117 113

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byallknownlanguages(Forexamples,seeGreenberg, 1963 andEvans&Levinson, 2009 ,togetherwiththelatter ’ snumerouspublishedresponses.)Onestrongcandidateforalanguage universalisthepropertyofvocalturn-taking.Themajorityof languageuseinvolvesconversationalinteractionsbetween twoormorepartiesandreliesontherapidswitchingofturns betweenagents(speakersorsigners).Inhumans,thetimingof theseturnsishighlysimilarnotonlywithinalanguage,but acrossalllanguagesstudiedtodate,includingsignedlanguages(Levinson, 2016 ;Stiversetal., 2009 ).Giventherapid timescaleatwhichturn-takingoccurs(~200ms),ascompared totherelativelyslowactofspeechproductionplanning (>600ms),successfulturn-takingmustinvolveintensivecognitivemultitasking,inordertosimultaneouslycomprehend meaningandplantheproductionofarapidyetcoherentresponse(Levinson, 2016 ).Thus,turn-takingisademanding, yetseeminglycommon,featureofhumanlanguagethatmay havedeepevolutionaryroots. Animalturn-takingbehavior Humansarenottheonlyanimalsthatemployturn-takingduringcommunication, supportingtheseputativedeeproots(Yoshida&Okanoya, 2005 ).Turn-takingisobservedthroughouttheanimalkingdom,andishypothesizedtosubservefunctionsincluding mateidentification/reunion,jointterritorydefense,andpair bonding.Inanimalcommunication,turn-takinghasbeendescribedas B alternatingsignaltransmissionbetweenparticipants,withdefinedreplylatency ^ (Yoshida&Okanoya, 2005 ,p.154)andcaninvolvedueting(reciprocalexchange betweenmale – femalepairs)orantiphonalvocalizations(alternatingcallandresponsebetweentwoormoreanimals). Suchvocalturn-takingisfoundinbothvocal-learningandnonlearninganimals,andinmanyspeciesitoccurssoonafter birth,suggestingamechanismthatisatleastpartiallyinnate. Turn-takingiswell-studiedinbirds,whereduetingandantiphonyarewidelyfound(Dahlin,Benedict,&Hauber, 2014 ; Henry,Craig,Lemasson,&Hausberger, 2015 ).Primatesalso displayvocalturn-taking,withevidenceacrossprosimians, monkeys,andlesserapes(Chow,Mitchell,&Miller, 2015 ; Lemassonetal., 2011 ;Mendez-Cardenas&Zimmermann, 2009 ;Snowdon&Cleveland, 1984 ). Turn-takinginbats Onlyasmallnumberofstudieshave exploredthepossibilityofturn-takinginbats;however,there isgoodevidencethatanumberofbatspeciesproduceantiphonal(callandresponse)vocalizations.Theseantiphonalcalls havebeenhypothesizedtoactascontactcallsfacilitatingindividualidentification,groupcohesion,and/orgroupterritorialdefense — similartowhatisseeninbirdsandprimates. Batsfromfourfamilies(Molossidae,Vespertilionidae, Phyllostomidae,andEmballonuridae)areknowntoperform avocalcallandresponseduringmother – pupreunions (Balcombe, 1990 ;Balcombe&Mccracken, 1992 ;deFanis &Jones, 1996 ;Esser&Schmidt, 1989 ;Knrnschild&von Helversen, 2008 ).Uponreturningtoaroost,mothersthathave beenindependentlyforagingcalltotheiroffspringtolocate them.Pupsrespondtothese B maternaldirectivecalls ^ with isolationcallsthatcontainindividualrecognitioncuestofacilitatefurthercallexchange,guidingthemothertothepup (Knrnschild&vonHelversen, 2008 ).Thus,coordinatedcontrolofthecallandresponse(antiphonalcalling)between motherandpupisessentialforreunionofthepairandthe survivaloftheoffspring.Thispresentsapromisingareafor th estudyofvocalturn-takinginbats,whereitwillbeimportanttodeterminewhetherthesecallsmeetthetemporalcriteria givenforvocalturn-taking(i.e.,acallandresponsewith definedlatencies;Yoshida&Okanoya, 2005 ). Vocalturn-takinghasbeenfoundinvampirebats(within thePhyllostomidaefamily),highlysocialbatsthatperform allogroomingandreciprocalfoodsharing(Carter, Skowronski,Faure,&Fenton, 2008 ).Adultwhite-winged vampirebats( Diaemusyoungi )produceaspecificduet-like FMsocialcallwhenfeeding,leavingroosts,orwhenseparatedoverlongdistances. D.youngi producetheseFMsocial callswithinadefinedlatency,mostoften300 – 350msafter hearingaconspecificcall(Carteretal., 2008 ).Mostofthese antiphonalinteractionsinvolvedasinglecallandresponse; however,uptofivealternatingcallsbetweenbatscouldbe observed.Thesebatsalsoperformedantiphonalvocalizations moreoftenwhentheywerephysicallyisolatedandcouldonly hearconspecificcalling,supportingthevocalizations ’ rolein long-distancerecognitionandgroupcohesion(Carteretal., 2008 ). Althoughitislikelythatturn-takingaroseduetomultiple convergentevolutioneventsacrosstaxa,understandinghow thisevolvedinsuchdistantspeciesasbatsandprimatesmight giveuscluesastohowvocalturn-takingaroseinhumans. Sharedgeneticfactorshavebeenshowntounderlie convergentlyevolvedtraitsacrossdisparatetaxa.Aclearexampleofthisistheselectionofgenesrelatedtohearing(such as prestin )inecholocationinbothbatsandcetaceans(Li,Liu, Shi,&Zhang, 2010 ;Shen,Liang,Li,Murphy,&Zhang, 2012 ).Thus,studyingexamplesofantiphonalbehavioracross batsandotherspecieswillrevealunderlyingbiologicalmechanismsforthisintriguingspoken-language-relevanttrait,and maypointtosharedoriginswithhumanturn-taking.Neurobiology,genetics,andthefutureHereinIhavediscussedevidencethatbatspresentexciting newmodelswiththepotentialtoilluminatethebiological underpinningsoftraitsrelevanttolanguage.Clearlythereis anurgentneedforfurtherethologicalworktobetterdefinethe rangeandfunctionsofbatvocalbehavior.Thiswouldallow comparisonsacrossdiversebatspecies,butimportantly,also 114 PsychonBullRev(2017)24:111 – 117

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acrosstaxaincludingsongbi rds,primates,andhumans. However,itisimportantnottostopatthebehaviorallevel, butalsotomakecoordinatedeffortstounderstandtheneurobiologicalandgeneticmechanismsthatbuildabraincapable ofthesecomplexbehaviors.Todate,suchstudieshavelargely beenrestrictedtohumansandbirds.Advancesingeneticsand neurobiologyarenowmakingitpossibletoinvestigatehow thesetraitsareencodedinbats,bridgingtheevolutionarygap betweenfindingsinhumanandaviansystems. Neurobiology Studyingtheneurobiologyoflanguagerelevanttraitsinbatshasthebenefitofdirectlyinvestigating amammalianbrain,andarangeoftechniquesarenowpossibletoaccuratelymeasurebrainstructureandactivity. Magneticresonanceimaging(MRI)hasbeenusedinbatsto demonstratebrainarchitectureandcochleaspecializationsrelatedtoecholocation(Hsiao,Jen,&Wu, 2015 ;Hu,Li,Gu, Lei,&Zhang, 2006 ),andfunctionalMRIhasshowncortical activationpatternsinbatsfollowingauditorystimuli (Kamada,Pekar,&Kanwal, 1999 ).Mostrecently,wireless electrophysiologyhasallowedsingle-cellrecordingoffreely behavingbats,revealingunprecedentedinsightintohowbat brainsencodethree-dimensionalinformationwhileinflight (Yartsev&Ulanovsky, 2013 ;Yartsev,Witter,&Ulanovsky, 2011 ).Theneurobiologicalmechanismsunderlyingtraitslike vocallearninghavebeenextensivelystudiedintheavian brain,andthereisnowabothaclearneedandthetechnical competencyforcomparableexperimentstobecarriedoutin mammaliansystemssuchasthebat.Conservedbrainstructure acrossmammalswillallowustousefindingsfrombatsto makedirectparallelswithhumanswhenconsideringtherole ofcorticalnetworksinvocalcommunicativebehavior.Such comparativeworkwillbecentraltoidentifyingcommonevolutionarythemesunderlyingthesecomplextraits. Genetics Rapidadvancesarealsobeingmadeatthemolecular level(e.g.,transcriptomesandgenomes)andinourabilityto performgeneticmanipulations.Todate,sequencedatafrom tenbatshavebeenreleased,givingsomeintriguingcluesinto theevolutionofecholocation,flight,andimmunity(Li,Wang, Rossiter,Jones,&Zhang, 2007 ;Parkeretal., 2013 ;Zhang etal., 2013 ).However,tounderstandtheevolutionofsocial communication,furtherChiropterangenomescoupledtoindepthbehavioralanalysiswillbeessential,ashasbeendemonstratedbythevaluableworkoftheAvianPhylogenomics Project(Pfenningetal., 2014 ;Whitneyetal., 2014 ).Overlaid withthis,transcriptomic(geneexpression)datawillgiveus directinsightintohowmolecularmechanismsfunctioninthe real-timeprocessingofthesetraits.Werecentlyidentified functionalgenenetworksviatranscriptomicsinthe P.discolor brain(Rodenas-Cuadrado,Chen,Wiegrebe,Firzlaff,& Vernes, 2015 ),demonstratingthefeasibilityofinterrogating themolecularpathwaysunderlyingcomplextraitsinthebat brain.Combiningsuchcutting-edgemolecularandneurobiologicaltechniquesinbatswithethologicalstudieswillreveal newinsightintotheencodingandfunctionofcircuitsinvolvedincomplexcommunicativebehaviorinthemammalianbrain. Thefuture Itisclearthatnosingleanimaloranimalbehavior canbeusedtoaccuratelymodellanguage.Thus,itiscrucial thatweexploreawiderangeoflanguage-relevanttraitsacross diversespecies.Batshaveenormouspotentialtocontributeto thisfield,openingupnewexperimentalavenuestounderstand howamammaldevelopsthesetraits,andhowthisdevelopmentcompareswiththatofmoredistantlyrelatedspecies,like birds.Takinganintegrativeapproachthatconsidersfindings frombirds,tobats,andbeyondwillprovideessentialinsights intothebiologicalencodingofcomplexcommunicationsystems,akeysteptowardunderstandingtheevolutionofhuman speechandlanguage.Authornote OpenaccessfundingprovidedbyMaxPlanckSociety (MaxPlanckInstituteforPsycholinguistics).Thisworkwasfundedby aMarieCurieCareerIntegrationGrantandbyaMaxPlanckResearch GroupGrant,bothawardedtoS.C.V.Theauthordeclaresthattheresearchwasconductedintheabsenceofanycommercialorfinancial relationshipsthatcouldbeconstruedasapotentialconflictofinterest, oranyinvolvementsthatmightraisethequestionofbiasinthework reported. 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