*Author ([email protected]) for correspondence Little Rock, Little Rock, AR72204,USA. Louisville, KY40292, USA. © 2014.PublishedbyTheCompanyofBiologistsLtd|JournalExperimentalBiology(2014)217,2163-2170doi:10.1242/jeb.101600 Received 19December 2013;Accepted3March2014 1 relatively ineffective andclumsy onland.Thegaitsoftheseinsects locomotion beloworonthewatersurface(Nachtigall,1974),but are such asdivingbeetlesandwaterstridersfacilitateefficient fortuitous. lacking suchtraits,escapefromthewatersurfaceusually is Milne andMilne,1978;Vogel, 1994;Huetal.,2003).Forspecies morphologies ofneustonicinsectsandspiders(Andersen,1976; generalities includethespecializedwater-treading behaviorsand death viadrowningorpredation.Conspicuousexceptionsto these slender kickingappendagesoftenleadstoafutilestruggleending in Additionally, therelativelylowphysicalresistanceofwaterto size makesthemvulnerabletoentrapmentbysurfacetensionforces. helpless whentheyfallontowater, inpartbecausetheirsmallbody uncommon innature(Vogel, 1994).Mostterrestrialarthropodsare Efficient locomotionattheair–waterinterfaceisrelatively Skototaxis KEY WORDS:Aquatic,Behavior, Forest,Formicidae,Neustonic, swimming atspeeds>3 assess theirswimmingability. Ten speciesshoweddirectedsurface into naturalandartificialaquaticsettingsinPeruPanamato swimming) intropicalarborealants.We dropped35speciesofants document sustained,directional,neustoniclocomotion(i.e.surface escape bywalkingorswimmingatthewatersurface.Herewe Exceptions tothisoutcomemostlyoccuramongripariantaxathat helplessly struggleandarequicklyeatenbyaquaticpredators. Upon fallingontothewatersurface,mostterrestrialarthropods S. P. Yanoviak Water surfacelocomotionintropicalcanopyants RESEARCH ARTICLE to includevariousspeciesoftropicalarborealants. These resultsexpandthelistoffacultativelyneustonicterrestrialtaxa and midlegs,respectively, whilethehindlegsproviderollstability. synchronized treadingandrowingmotionsofthecontralateralfore when swimming;theygeneratethrustatthewatersurfacevia Pachycondyla skototaxis). Analysesofhigh-speedvideoimagesindicatethat water bydirectingtheirswimmingtowarddarkemergentobjects(i.e. workers ofOdontomachusbauri association withdirectedaerialdescentbehavior. Experimentswith genera indicatesparallelevolutionandatrendtowardnegative the surface.Thephylogeneticdistributionofswimmingamongant movement. Theremainingspeciesshowednolocomotorycontrolat swimming abilitycharacterizedbyrelativelyslowbutdirected absolute speeds>10 INTRODUCTION ABSTRACT Department of Biology, Louisville, 139Life SciencesBuilding, of University of Department The veryspecializedlegsofobligatepelagicandneustonictaxa spp. and 1, * andD.N.Frederick
2 cm Department of Biology, at Arkansas of University of Department O. bauri body s − 1 . Ten otherspeciesexhibitedpartial lengths use amodifiedalternatingtripodgait showed thattheyescapefromthe s − 1 , withsomeswimmingat 2 example, thehydrophobictarsiofriparian with highefficiency usingthesamegaitsandappendages.For contrast, riparianarthropodsfrequentlytreadonbothlandandwater by terrestrialspeciesinthesameclades(Andersen,1976).By often arekinematicallydistinctfromthealternatingtripodgaitused described indetailfor workers andbroodonthewatersurface.Thisbehaviorwas remarkably well.Inthesimplestcase,entirecoloniesformraftsof Nonetheless, afewantspeciesareabletolocomoteonorinwater but completeimmersiontypicallyisproblematicforants. foraging (Young andHermann,1980;DejeanSuzzoni,1997), some speciesusewatersurfacetensiontotheiradvantagewhen particularly unlikelytointeractfavorablywithwater. Workers of species (Franklinetal.,1977;DuBoisandJander, 1985). a watersurfacewithmodifiedorunmodifiedgaits,dependingonthe insect taxa(e.g.mantids,cockroaches)arealsocapableoftraversing 2003; Suter, 2013).Althoughlesscommon,afewentirelyterrestrial water whileothersdonot(SuterandWildman, 1999;Suteretal., and land(Strattonetal.,2004);someuseamodifiedgaitwhenon Sutton, 2012).Manyspidersalsolocomoteequallywellonwater from bothlandandwater(BurrowsPicker, 2010;Burrowsand modified hindlegsoftridactylidgrasshoppersfacilitatelarge jumps them toalightonwaterorvegetation(Burrows,2013),andthe 2011), butalsooccursinsome falling fromthe canopytotheunderstory (D.N.F. andS.P.Y., of Panamashowthatantsconstitute ca.70%ofwinglessarthropods However, many speciesdonotglide,andsurveysinlowlandforest understory byglidingtonearby treetrunks(Yanoviak etal.,2005). to theircolonies,andsomespecies avoidlandinginthehazardous (Saint-Paul etal.,2000;Small al.,2013).Lostworkersarecostly by fishthatconsumeterrestrial insectstrappedinthewatersurface and riparianareasareespeciallydangerous;theyofteninhabited and complexterrain(Yanoviak etal.,2011). Tropical floodedforests Longino andColwell,1997),wheretheyfaceunfamiliarpredators fall fromthecanopytoforestunderstory(Haemig,1997; and Oliveira,2007;Klimesetal.,2012).Arborealantsfrequently high abovetheground(HölldoblerandWilson, 1990;Rico-Gray tropical forests,andmanyspeciesnestforageintreecrowns water surfacelocomotioninvariousNeotropicalants. we describetheoccurrence,basickinematicsanddirectionality of lundii carli (DuBois andJander, 1985),andcertainleaf cutterants( (Robson, 2010),Camponotus Polyrhachis sokolova on watersurfacesisknowninonlyafewanttaxa,including Nepenthes for insectpreybycrawlingorswimmingintothewaterheld personal observation),andworkersofCamponotusschmitzi walk beneaththesurfaceofpuddlesonforestfloor(S.P.Y., such asEctatommaruidum (Robson, 2010;S.P.Y., personalobservation).Otherrainforesttaxa, As small,terrestrialandobligatelycursorialorganisms, antsseem Ants areamongthemostabundantandconspicuousarthropods in ) inhabitingAmazonianfloodedforest(Adis,1982).Here pitchers inAsia(Bohnetal.,2012).Directedlocomotion Solenopsis workers ofAustralianmangroveforest in CentralAmerica,willvoluntarily spp. inMalaysiaandNorthAmerica Wasmannia (Adams etal.,2011; Mlotetal., Hydrophorus and Pheidole Acromyrmex flies allow species forage 2163
The Journal of Experimental Biology Ponerinae Paraponerinae Dolichoderinae 2164 methods. *Epigeic species. intheMaterials and Each testedspecies wasassignedtooneofthreegroups basedonasemi-quantitativeassessment ofswimmingabilityasdescribed Taxon traversing seasonalfloodwaters(Irmler, 1973). ground-dwelling beetlesuseskototaxistolocatetreetrunkswhen darkest nearbylandmarks(Campan,1997).Indeed,Amazonian surface reflectsambientlight,andtreetrunksconsequentlyarethe effective inecotonal,riparianandfloodedforestsettings;thewater (Taylor, 1988;Campan,1997).Skototaxismaybeespecially skototaxis, althoughreasonsforthebehaviorarenotalwaysobvious skototaxis (DuBoisandJander, 1985)].Various insects exhibit suggest thattheyspecificallymovetowarddarkobjects[i.e. mantids (Miller, 1972).Otherstudiesofantstreadingonwater escape maneuverstowardnearbyemergent objects,asdoswimming Likewise, antslandingonwatershoulduselocalcuestodirecttheir locate treetrunksduringafall(Yanoviak andDudley, 2006). Nicholson etal.,1999),andglidingcanopyantsusevisualcuesto chemical senses(Hölldobler, 1980;HölldoblerandWilson, 1990; from awatersurface. it islikelythatsomespeciespossesstraitsfacilitatingtheirescape unpublished). Giventhatfallingantswilloccasionallylandinwater, RESEARCH ARTICLE Table Pseudomyrmecinae Formicinae Ecitoninae Ectatomminae Myrmicinae Paraponera clavata Hypoponera distinguenda Wasmannia rochai Solenopsis Azteca trigona P. foetida Pachycondyla apicalis O. Odontomachus bauri Solenopsis Procryptocerus belti Pheidole Pheidole Nesomyrmex anduzei