Morphology of the tracheal system of camel spiders (Chelicerata: Solifugae)

12 Pages·2016·4.2 MB·English

ArthropodStructure&Development45(2016)440e451
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Arthropod Structure & Development
journal homepage: www.elsevier.com/locate/asd
Morphology of the tracheal system of camel spiders (Chelicerata:
Solifugae) based on micro-CT and 3D-reconstruction in exemplar
species from three families
Sandra Franz-Guess a,*, Bastian-Jesper Klußmann-Fricke b, Christian S. Wirkner b,
Lorenzo Prendini c, J. Matthias Starcka
aLudwig-Maximilians-Universita€tMünchen,BiocentereDepartmentofBiologyII,FunctionalMorphologyGroup,GroßhadernerStr.2,82152,Planegg-
Martinsried,Germany
bUniversita€tRostock,Allgemeine&SpezielleZoologie,InstitutefürBiowissenschaften,Universita€tsplatz2,18055,Rostock,Germany
cDivisionofInvertebrateZoology,ArachnologyLab,AmericanMuseumofNaturalHistory,CentralParkWestat79thStreet,NewYork,NY,10024-5192,USA
a r t i c l e i n f o a b s t r a c t
Articlehistory: WestudiedthetrachealsystemofexemplarspeciesrepresentingthreefamiliesofSolifugaeSundevall,
Received19May2016 1833,i.e.,GaleodesgrantiPocock,1903,AmmotrechulawasbaueriMuma,1962andEremobatessp.,using
Accepted5August2016 mCT-imaging and 3D-reconstruction. This is the first comparative study of the tracheal system of
Availableonline30August2016 Solifugaein85yearsandthefirstusinghigh-resolutionnondestructivemethods.Thetrachealsystem
wasfoundtobestructurallysimilarinallthreespecies,withbroadmajortracheaepredominantlyin
Keywords: the prosoma as well as anastomoses (i.e., connections between tracheal branches from different
Ammotrechulawasbaueri
stigmata)intheprosomaandopisthosoma.Differencesamongthethreespecieswereobservedinthe
Galeodesgranti
presence or absence of cheliceral air sacs, the number of tracheae supplying the heart, and the
Eremobatessp.
Respiratorysystem ramification of major tracheae in the opisthosoma. The structure of the tracheal system with its
Micro-CT extensivebranchesandsomeanastomosesisassumedtoaidrapidandefficientgasexchangeinthe
3D-reconstruction respiratorytissuesoftheseactivepredators.Thelargediameterofcheliceraltracheae(airsacs)oftaxa
with disproportionally heavier chelicerae suggests a role inweight reduction, enabling solifuges to
reachgreaterspeedsduringpredation.Theairsacsmayalsopermitmorerapidandefficientgaseous
exchange,necessarytooperatethemusculatureofthesestructures,therebyimprovingtheirusefor
predationinanenvironmentwherepreyisscarce.
©2016ElsevierLtd.Allrightsreserved.
1. Introduction probably more than once within acariform mites (Alberti and
Coons,1999).Theindependentevolutionaryoriginsoftracheaein
Terrestrial chelicerates (Arachnida) respire using book lungs, spidersandothertracheatearachnids(sensuWeygoldtandPaulus,
tracheae, or a combination thereof. Many authors regard book 1979)issupportednotonlybytheirrelativephylogeneticpositions,
lungs as the plesiomorphic condition (Dunlop,1997; Scholtz and butalsobythemorphologicaldifferencesamongtheirrespective
Kamenz, 2006; Kamenz et al., 2008), whereas a tracheal respira- trachealrespiratorysystems.
torysystemisconsideredderived.Tracheaeevolvedatleasttwice The tracheaeof spidersopenthrougha singlestigma situated
independently within Arachnida, regardless of which hypothesis medially on the ventral surface of the opisthosoma, or through
forarachnidphylogenyisadopted(e.g.,WeygoldtandPaulus,1979; stigmata emerging from the atrium of the former book lungs
WheelerandHayashi,1998;Giribetetal.,2002;Shultz,1990,2007; (Schmitz, 2013, 2016). The tracheae may be simple or branched,
Pepato et al., 2010; Regier et al., 2010; Sharma et al., 2014), and with a brush-like appearance, but do not anastomose (Bromhall,
1987). Many spider taxa possess both tracheae and book lungs
but, in some derived taxa, book lungs have been completely
* Correspondingauthor. replacedbytracheae(e.g.,Opell,1998).Thetracheaeofmostspi-
E-mailaddresses:[email protected](S.Franz-Guess),bklussmann@gmx. ders float freely in the hemolymph and do not reach the tissues
net (B.-J. Klußmann-Fricke), [email protected] (C.S. Wirkner), lorenzo@
(Foelix, 2010; Strazny and Perry,1987; Schmitz and Perry, 2000;
amnh.org(L.Prendini),[email protected](J.M.Starck).
http://dx.doi.org/10.1016/j.asd.2016.08.004
1467-8039/©2016ElsevierLtd.Allrightsreserved.
S.Franz-Guessetal./ArthropodStructure&Development45(2016)440e451 441
Schmitz,2016).Hemocyaninsfunctionasoxygen-carryingproteins across the order: Galeodidae Sundevall,1833 was represented by
thatprovidetheconvectivetransportofrespiratorygasesfromthe twofemaleGaleodesgrantiPocock,1903fromEgypt,preservedin
trachealendingstothetissues,andviceversa. ethanol in the collection of the Biocenter at the Ludwig-Max-
Unlikespiders,tracheatearachnids (i.e.,“Acari”,Ricinulei,Sol- imilians-Universita€tMünchen(inventorynumberP-24-GG6andP-
ifugae, Pseudoscorpiones, and Opiliones) possess paired stigmata 24-GG7). Ammotrechidae Roewer, 1934 was represented by one
on the prosoma, the opisthosoma, or both (Beier,1931; Ka€stner, female Ammotrechula wasbaueri Muma,1962 obtained alive from
1931a; Alberti and Coons, 1999; Coons and Alberti, 1999; Ho€fer Arizona,U.S.A.,fromwww.bugsofamerica.com,andnowstoredat
et al., 2000; Klußmann-Fricke and Wirkner, in press). These taxa theZoologischeSammlungUniversita€tRostock(inventorynumber
relyexclusivelyontracheaeforrespiration.Theircomplextracheal ZRSO So 012). Eremobatidae Kraepelin,1901 was represented by
system comprises major tracheal branches (sometimes anasto- sevenadultmalesofaspeciesofEremobatesBanks,1900alsoob-
mosing),fromwhichminorbranchesemergeandramifythrough tained alive from Arizona, U.S.A., from www.bugsofamerica.com,
thebodytotheoxygen-consumingtissues.Tracheatearachnidsdo andnowstoredattheZoologischeSammlungUniversita€tRostock
not possess hemocyanins (Markl, 1986; Rehm et al., 2012) that (inventorynumbersZSROSo010e011andZRSOSo013e017).
wouldfunctionasoxygen-bindingcarrierproteinsandthus,inthe
absence of the hemolymph providing a convective system, the 2.2. Micro-computedtomography(mCT)
tracheae transport the respiratorygases directly to and from the
tissues. Specimens of G. granti were stained using a solution of 100%
Amongtracheatearachnids,thecamelspidersorSolifugaeSun- ethanol containing 1% iodine for mCT-imaging (Metscher, 2009).
devall,1833(ca.1000species;Levin,2013)are unusualbecauseof Bothspecimenswereretainedinthestainingsolutionfor15daysto
theirhighlyactivelifestyle(Roewer,1934;Punzo,1993).Theiractive ensurethoroughpenetrationofcuticleandtissue.Livespecimens
huntingisassociatedwithcomparativelyhighratesofmetabolism of A. wasbaueri and Eremobates sp. were exposed to OsO4 vapor
andoxygenconsumption(LightonandFielden,1996;Lightonetal., (EMS-ElectronMicroscopySciences,Hatfield,PA,U.S.A.)for20min
2001). The complex tracheal system of Solifugae presumably tothoroughlystainthetrachealwalls.OsO4stainsthewaxesinthe
evolved to support the high oxygen demand of their tissues. The epicuticlebecauseithasaparticularlyhighaffinityforfattyacids.
tracheaeofsolifugesextendthroughoutthebody,reachingintothe Furthermore,duetothethinwallsofthetracheae,atleastsomeof
peripheral regions. Major branches ramify and anastomose with theOsO4alsopenetratesthetracheaeandstainsthesurrounding
contralateraltracheaeforminganextensivelyinterconnectedrespi- tissues(i.e.thetrachealepithelium).Thestainedspecimenswere
ratory network (Ka€stner,1931a). The remarkable similarity of the frozenat(cid:1)20(cid:3)C,thawed,andthelegsremovedpriortoscanningas
complextrachealsystemofsolifugestothatofinsectshasbeencited describedbyIwanetal.(2015).
asanexampleofmorphologicalconvergence(Wigglesworth,1983). mCT-imaging was performed with a Phoenix nanotome®
Themorphologyofthesolifugetrachealsystemwaspreviously (Phoenixjx-ray, GE Sensing & Inspection Technologies, Alzenau,
described by Kittary (1848), Bernard (1896), Ka€stner (1931a) and Germany)high-resolutionmCT-systeminnormalresolutionmode
Roewer(1934).Ka€stner's(1931a)illustrationofthemajortracheal forG.granti.High-resolutionmodewasusedforA.wasbaueriand
branches remains the most detailed and is frequently referred to Eremobatessp.Theprogramdatosjxacquisition(target:molybde-
(MillotandVachon,1949;Hennig,1967;Klann,2009;Punzo,2012; num, mode: 0e1; performance: 8e13 W; number of projections:
Hsia et al., 2013; Westheide and Rieger, 2013). Ka€stner's (1931a) 1080e2400; detector timing: 1000e1500 ms) was used for both
analysisofthetrachealsystemwasbasedondissectionandillus- resolution modes. Specimens of A. wasbaueri and Eremobates sp.
trationofthreeexemplarspecies(GaleodesaraneoidesPallas,1772, were scanned at the Microscopy and Imaging Facility of the
GaleodescaspiusBirula,1890,andaspeciesofSolpugaLichtenstein, American Museum of Natural History, New York, resulting in a
1796). voxel size of 2e10 mm. The software datosjx 2 reconstruction
In the present study, we reinvestigate the tracheal system of (GeneralElectricDeutschlandHoldingGmbH,Frankfurt-am-Main,
three species of Solifugae using modern non-invasive imaging Germany) and VGStudio MAX 2.2.6 (Volume Graphics GmbH,
techniques (mCT-imaging and 3D-reconstruction), document the Heidelberg,Germany)wereusedforimageprocessing.Specimens
respiratory system in situ, and provide an analysis of the fine of G. granti were scanned at the Zoologische Staatssammlung,
branchesandramificationsofthetrachealsystemofSolifugae.We Munich, using two different settings, resulting in two different
hypothesize that the tracheae function not only as the sites for resolutions to provide a single complete overview (voxel size
gaseous exchange but also as a convective system because sol- 25mm)andtwomoredetailedscans(voxelsize5mm).Theimage
ifugeslackhemocyaninsasoxygen-carryingproteins.Wepredict data obtained for G. granti (voxel size 5.5 mm and 25 mm) was
thatthefunctionaldemandsonoxygentransportintracheaeand converted to TIF-format using Fiji (ImageJ 1.49(cid:3)) for further
the mechanical principles of flexible tubing systems may have analysis.
selectedforatrachealsystemthatisinmanyrespectsanalogousto
thetrachealrespiratorysystemofinsects.Thepresentstudyaims 2.3. 3D-reconstruction
to clarify the organization of the major branches of the tracheal
system of Solifugae, and detect morphological disparity among The body surface, tracheal system, prosomal ganglion, heart,
three families of this arachnid order. The finer branches of the and intestinal tract of G. granti were reconstructed using surface
tracheal system and their connection to various tissues are rendering in Amira 6.0.0 (Mercury Computer Systems Inc.,
analyzedinacompanionpaperinthisissueofArthropodStructure Chelmsford, MA, USA). The respective tissues of each mCT-image
&Development(Franz-GuessandStarck,2016). werelabeledusingagraphicpen.Startingattheprosomalstigmata,
allconnectingtrachealstructuresweremarkedincyan(Fig.1).The
2. Materialandmethods digestivesystem,excludingthemidgutdiverticula,wasmarkedin
brown,theheartinred,andtheprosomalganglioninyellow.Areas
2.1. Taxonsampleandmaterialexamined withoutanyvisibleconnectiontopreviouslyreconstructedorgans,
due to image and preservation artifacts, were marked in a pale
Westudied exemplarspeciesrepresentingthreesolifugefam- versionoftherespectivecolor.SelectedmCT-imagesandrespective
iliestoinvestigatemorphologicaldisparityinthetrachealsystem labelingareprovidedinFig.1todocumenthowsegmentedimages
442 S.Franz-Guessetal./ArthropodStructure&Development45(2016)440e451
Fig.1. ExamplesoforiginalmCT-imagesdocumentingthesegmentationoftracheaefor3D-reconstructionofGaleodesgranti.(A)Cross-sectionthroughthebaseofthechelicerae,the
rostrumandthecoxaeofthepedipalps(originalmCT-image#1502).Thestrongmusculatureofthecheliceraeisevidentincrosssection,theesophagusisinthemiddleofthe
triangularrostrumand,dependingontheanatomicalorientation,themusculatureofthepedipalpalcoxaeandtrochantersaresectionedlongitudinally.Crosssectionsofthedistal
pedipalpalsegmentsandlegsegmentsareevidentintheperiphery.(B)SamesectionasinAbutwithtracheaelabeledcyan.Darkareasaroundtracheaerepresenthemolymph-
filledspaces(C)Cross-sectionthroughthethirdprosomalsegment(originalmCTimage#1194).Theprosomalstigmaisonthedextralsideoftheimage,theH-shapedapodemeof
thethirdsterniteisevidentmedially,supportingtheanteriorpartofthemidgutwithadjoiningprosomalmidgutdiverticula.(D)SamesectionasinCbutwithtracheaelabeled
cyan.ThehemolymphspacesinthisregionaresmallerthaninB.Thelateralcheliceral,mainposteriorprosomalandventralprosomaltracheaearepresentinadditiontoall
tracheaeofthelegsandpedipalps.(E)Cross-sectionthroughthefourthopisthosomalsegment,posteriortothesecondopisthosomalstigmata(originalmCTimage#347).The
opisthosomaisalmostentirelyfilledwithmidgutdiverticula.Thedarkspacedorsaltothemidgutdiverticulaisapreservationartifact.(F)SamesectionasinEbutwithtracheae
labeledcyan.Asidefromsmallhemolymphspaces,onlythetracheaeofthefourthlegandthemainopisthosomaltracheaeIIarepresent.Abbreviations:a:atrium;ac:anterior
cheliceraltrachea;ap:anteriorpedipalpaltrachea;apd:apodeme;ar:artifact;c:chelicerae;cm:cheliceralmusculature;e:esophagus;hl:hemolymph;l:leg;lc:lateralcheliceral
trachea;lm:legmusculature;l1e4:legIeIVtracheae;m:bodymusculature;mg:midgut;mgd:midgutdiverticula;mo2:mainopisthosomaltracheaII;mpp:mainposterior
prosomaltrachea;p:pedipalp;pc:posteriorcheliceraltrachea;pcx:pedipalpcoxa;pm:pedipalpmusculature;pp:posteriorpedipalpaltrachea;ps:prosomalstigma;pt:pedipalp
trochanter;vp:ventralprosomaltrachea.
S.Franz-Guessetal./ArthropodStructure&Development45(2016)440e451 443
translate into raw data for the 3D-reconstruction. Surface- appearinginflatedcomparedtoothertracheae.Thesecheliceralair
reconstructions of the tracheal system and body surface of A. sacsaresmaller(Fig.3B)inA.wasbaueri,andonlytheanteriorand
wasbaueriandEremobatessp.wereproducedusingVGStudioMAX posteriorcheliceraltracheaeareinflatedandsituatedintheante-
2.2.6 (Volume Graphics GmbH, Heidelberg, Germany) or Imaris riorpartofthecheliceraeandbothcheliceralfingers.Theanterior
7.0.0 (Bitplane©, Zurich, Switzerland). The complete sets of mCT- andposteriorcheliceraltracheaearenotinflatedinEremobatessp.
images are deposited with MorphoBank (O'Leary and Kaufman, (ac,pc;Fig.3C).
2012)athttp://morphobank.org/permalink/?P2422.
3.1.3. Gangliontracheae
2.4. Imageprocessing The prosomal ganglion trachea (pg; Figs. 4, 6) originates from
themainanteriorprosomaltracheainthesegmentwhichbearsthe
Figures were arranged into plates using Adobe Illustrator CS2 second leg. It first extends medially and then bends ventrally to
(AdobeSystemsIncorporated).Bitmapimageswereembeddedinto entertheprosomalganglion(pg;Figs.2,3B,C,4).Thedorsalpro-
CorelDrawX3filesanddigitallyeditedusingCorelPhotoPaintX3. somaltrachea,whichoriginatesanteriortotheprosomalganglion
The interactive PDF was created using Adobe Acrobat 9 Pro trachea, extends dorsally, alongside the prosomal ganglion and
Extended(AdobeSystemsIncorporated). towardthemiddleoftheprosoma,whereitramifiesfurther(dp,
pg; Figs. 2e4, 6) supplying the extrinsic musculature of the
3. Results chelicerae.Theventralprosomaltracheaoriginatesfromthelateral
prosomal trachea, immediately posterior tothe prosomal stigma,
The description of the tracheal morphology is based on the andextendsventrallytowards the prosomalganglion (fora clear
reconstructionofG.grantiwithdifferencesobservedinthetracheal view of the origin of the ventral prosoma trachea, rotate Fig. 3A
systemsoftheotherexemplarspeciesnotedwhererelevant. ventrally using the interactive 3D-image function). The ventral
prosomal tracheae of A. wasbaueri and Eremobates sp. are less
3.1. Prosoma pronounced,anddonotreachasfaranteriorly,asinG.granti(vp;
Figs.3,4,6).Thegeneralpatternoftrachealsupplytotheprosomal
3.1.1. Stigmataandmajortracheae ganglionissimilarinallthreespecies.
Thenetworkofmajortracheae(>100mmindiameter)ismost
prominentinthe prosoma. Fifteenmajor trachealtrunkscanbe 3.1.4. Lateralandposteriorprosomaltrachea
identified in the prosoma (Figs. 2, 6; Table 1). The prosomal Thelateralprosomaltrachea(lp;Figs.4,6)andthemainpos-
stigmata of the tracheal system open laterallyand ventrally be- terior prosomal trachea (mpp, Figs. 2e4, 6) originate at the pro-
tweenthesecondandthirdlegs(Figs.2e4)inthesejugalfurrow. somalstigmaandsupplytheposteriorpartsof theprosoma.The
Three main tracheal trunks, the main anterior prosomal (map) lateral prosomal trachea divides into anterior and posterior
trachea, the main posterior prosomal (mpp) trachea, and the branches.Theanteriorbranchextendsventrallyandbecomesthe
lateral prosomal trachea (lp), originate from an atrium immedi- ventralprosomaltrachea(lp,vp;Figs.2e4,6).Theposteriorbranch
atelyinternaltoeachstigma.Themainanteriorprosomaltrachea extendsobliquelydorsallyandposteriorlywhereitramifiesfurther,
extends to the anterior segments, whereas the lateral prosomal supplying the area posterior to the meso- and metapeltidium. In
tracheaeandthemainposteriorprosomaltracheaextendtothe bothspecimensofG.grantistudied,thesinistrallateralprosomal
posterior segments. The main posterior prosomal trachea con- tracheawasmoreprominentthanthedextral(lp;Fig.4).Themain
nectstothetrachealsystemoftheopisthosoma.Thedextraland posteriorprosomaltracheaextendsstraightposteriorly,givingrise
sinistral main anterior prosomal tracheae anastomose immedi- to the tracheae of the third and fourth legs. The main posterior
atelyanteriortotheprosomalganglion(map,mpp;Figs.2e4,6). prosomaltracheacontinuestotheposteriorborderoftheprosoma
ThelateralprosomaltracheaearelessdevelopedinA.wasbaueri whereitconnectstothemainlateralopisthosomaltrachea(mpp,
andEremobatessp. mlo; Fig. 3). The lateral prosomal tracheae of A. wasbaueri and
Eremobates sp. are less pronounced than those of G. granti (lp;
3.1.2. Cheliceraltracheae Fig.3).
Theanterior,posteriorandlateralcheliceraltracheaesupplythe
chelicerae(Figs.3,6).Theanteriorandposteriorcheliceraltracheae 3.1.5. Pedipalpandlegtracheae
originatefromthemainanteriorprosomaltracheaanteriortothe The tracheae supplying the pedipalps, legs I and II originate
prosomal ganglion and dorsal to the anastomosis of the main segmentallyfromthemainanteriorprosomaltracheawhereasthe
anteriorprosomaltrachea;thelateralcheliceraltracheaemanates tracheaeoflegsIIandIVemanatefromthemainposteriorproso-
dorsallyfromthemainanteriorprosomaltrachea,slightlyanterior maltrachea(map,mpp;Figs.2e4,6).Severalanteriorandasingle
totheoriginofthetracheaeofthesecondwalkingleg.Thelateral posteriorpedipalpaltracheaeoriginatefromtheanteriorendofthe
cheliceral tracheae extend first dorsal and then anterior to the main anterior prosomal trachea. All pedipalpal tracheae extend
chelicerae.ThelateralcheliceraltracheaeofA.wasbaueriandEre- throughtheentirelengthof thepedipalpintothetarsus(ap,pp;
mobates sp. originate from the main anterior prosomal trachea Figs.2,3).Theanteriorpedipalpaltracheaextendstothetipofthe
directly at the stigmata. The lateral cheliceral tracheae of both pedipalp without branching, whereas the posterior pedipalpal
speciesaremuchmorepronouncedthanthoseofG.grantiand,inA. trachea branches shortly after its origin into two main trunks,
wasbaueri, give rise to a pair of tracheae which extend ante- mergesagaininthefemurandbranchesagaininthetibia(ap,pp;
romediallyandthencurveventrallyalongthemidlineofthebody. Figs.2,3).ThetracheaoflegIoriginatesimmediatelyposteriorto
Thesetracheaecontinueinparalleltotheanterioranastomosisof theposteriorpedipalpaltracheafromthemainanteriorprosomal
themainanteriorprosomaltracheaewheretheyanastomosewith trachea (l1, pp, map; Figs. 2e4, 6), and onlyone trachea extends
the latter. The cheliceral tracheae of all three species branch throughallsegmentsofthelegtothetarsus.ThetracheaoflegII
extensively on entering the chelicerae, forming various tracheal branches from the main anterior prosomal trachea, immediately
tubesthatextendintothecheliceralmusculature.Thesecheliceral anteriortotheprosomalatrium(l2,Figs.2e4,6).AswithlegI,only
tracheae do not anastomose. Their main branches display some onetracheaextendstothetarsus:althoughoriginatingastwo,the
expansion (i.e., the diameter is wider than at their origin), smaller branch only reaches the trochanter where the two
444 S.Franz-Guessetal./ArthropodStructure&Development45(2016)440e451
Fig.2. Lateral(A),dorsal(B)andventral(C)viewsof3D-reconstructionofmajortrachealbranches(cyan)andcentralnervoussystem(yellow),digestivetract(brown)andheart
(red)ofGaleodesgrantibasedonmCTserialimages.(A)Onepairofstigmataintheprosoma,twopairsofstigmataattheposteriormarginofthethirdandfourthopisthosomal
segments,respectively,andasinglestigmainthefifthopisthosomalsegmentindicatedbyredarrows.Eachprosomalstigmaopensintooneofthemainanteriorprosomaltracheae,
andthesetwotracheaeleadtotheotherprosomaltracheae.Eachofthethreeopisthosomalstigmatacontinuesintoamainopisthosomaltracheaandtheseleadtotheother
opisthosomaltracheaesuchasthosefortheheart,genitaliaanddigestivetract.(B)Thebilateralnatureofthetrachealsystemisevidentinboththeprosomaandopisthosoma.The
tubularheartisprominentinthedorsalopisthosomaasarethetracheaeofthechelicerae,pedipalpsandlegs.Thecheliceraltracheaeformairsacsintheanteriorhalfofthe
chelicerae.Thelegandpedipalpaltracheaeextendintothetarsioftheirrespectiveextremities.(C)Thebilateralpatternoftracheaeintheprosomaandopisthosomaisevidentin
relationtothefusedcentralgangliathatextendlateralbranchestotheprosomalandopisthosomaltissuesandorgans.Thelocationoftheprosomalstigmata,eachopeningintoone
ofthemainanteriorprosomaltracheae,isindicatedbyredarrows.Eachopisthosomalstigmaopensintooneofthemainopisthosomaltracheae.Thetracheaeoftheprosomaand
opisthosomaconnecttooneanotherthroughthemainposteriorprosomaltracheaandthemainlateralopisthosomaltracheaatthejunctionofprosomaandopisthosoma.Ab-
breviations:ac:anteriorcheliceraltrachea;ap:anteriorpedipalpaltrachea;as:airsac;dp:dorsalprosomaltrachea;g:genitaltrachea;h:hearttrachea;l1el4:legIeIVtracheae;lc:
lateralcheliceraltrachea;lp:lateralprosomaltrachea;map:mainanteriorprosomaltrachea;mlo:mainlateralopisthosomaltrachea;mo1emo3:mainopisthosomaltracheaeIeIII;
mpp:mainposteriorprosomaltrachea;pc:posteriorcheliceraltrachea;pg:prosomalgangliontrachea;pp:posteriorpedipalpaltrachea;vp:ventralprosomaltrachea.Disruptions
inthecourseofthemainlateralopisthosomaltracheaareimageandpreservationartifacts.Areaswithoutanyvisibleconnectiontopreviouslyreconstructedtracheaeandorgans,
duetoimageandpreservationartifacts,indicatedinpaleversionsofrespectivecolors.
branchesmerge.ThetracheaeoflegsIIIandIVareextensionsofthe observed at the base of the appendages of A. wasbaueri and Ere-
mainposteriorprosomaltrachea.Twomaintrachealtrunksenter mobatessp.butthefullextentofthetracheaeinthelegsofthese
thelegsandmergeinthefemur(l3,l4;Figs.2,3).Allmaintracheae species is unknown because the legs were removed prior to
from legs IeIV extend into the tarsus. A similar situation was scanning.
S.Franz-Guessetal./ArthropodStructure&Development45(2016)440e451 445
Table1
NewlyproposedterminologyformajortracheaeinprosomaofSolifugaecomparedwithtraditionalterminologyofKa€stner(1931a).
Newterminology Abbreviation TerminologyofKa€stner(1931a)
Mainanteriorprosomaltrachea map Truncusprincipalis
Anteriorcheliceraltrachea ac Ramuscheliceralis
Posteriorcheliceraltrachea pc Ramuscheliceralisaccessorius
Lateralcheliceraltrachea lc Ramuslateralisanterior
Prosomalgangliontrachea pg Ramuscerebralis
Dorsalprosomaltrachea dp Ramusdorsalis
Ventralprosomaltrachea vp Ramustransversalis
Lateralprosomaltrachea lp Ramusposteriorlateralis
Mainposteriorprosomaltrachea mpp Ramusposteriormedialis
Anteriorpedipalpaltrachea ap Ramuspedipalpiaccessori
Posteriorpedipalpaltrachea pp Ramuspedipalpi
LegtracheaI l1 RamuspedisI
LegtracheaII l2 RamuspedisII
LegtracheaIII l3 RamuspedisIII
LegtracheaIV l4 RamuspedisIV
3.2. Opisthosoma ramifies before connecting with the main lateral opisthosomal
tracheawhereas,onthedextralside,theposteriorbranchgivesrise
3.2.1. Stigmataandmajortracheae to the heart trachea, before connecting with the main lateral
The stigmata of the opisthosoma are situated medially at the opisthosomaltrachea(mlo,h;Figs.2,3,5,6).Thehearttracheais
posteriormarginofsternitesIIIeV(redarrowsinFigs.2,3,5,6).The situatedimmediatelyventraltotheheart(h;Fig.2).Asitextends
stigmataofopisthosomalsegmentsIIIandIVarepairedandsitu- anteriorly,thehearttracheadividesoncepriortoconnectingtothe
atedincloseproximity.ThestigmaonopisthosomalsegmentVis main lateral opisthosomal trachea in the first opisthosomal
unpaired.Amainopisthosomaltracheaoriginatesfromeachstigma segment(h,g;Figs.2,3A,6).Posteriorly,thehearttracheabranches
supplyingadistinctregionoftheopisthosoma;i.e.,mainopistho- ineachopisthosomalsegment(h;Fig.5).The morphologyof the
somaltracheaIprimarilysuppliesopisthosomalsegmentsIeIIIas hearttracheaisdistinctlydifferentinA.wasbaueriandEremobates
wellastheheart,mainopisthosomaltracheaIIprimarilysupplies sp.(see3.2.6).
opisthosomal segment IV, and main opisthosomaltracheaIII pri-
marilysuppliesopisthosomalsegmentVeVII.Intheammotrechid 3.2.4. MainopisthosomaltracheaII
and eremobatid exemplars, however, the main opisthosomal tra- ThemainopisthosomaltracheaIIoriginatesatthestigmaofthe
chea II supplies the entire opisthosoma posteriorly to the fourth fourth opisthosomal segment and divides into three major
opisthosomalsegment.Inallspeciesstudied,themainopisthoso- branches, the anterior, posterior and ventral branches (mo2;
maltracheaeIeIIIareconnectedbywayofthemainlateralopis- Figs.2,3,5,6).Theanteriorbranchextendsdorsallyanddivides
thosomaltracheawhichrunsbilaterallyalongthemidgutthrough oncebeforeconnecting tothe main lateralopisthosomaltrachea
the entire opisthosoma and forms anastomoses at various points andcontinuingdorsally(mo2,mlo;Figs.2,3,5,6).Theposterior
with different branches there of (mlo, mo1e3; Fig. 5; Table 2). branch of the main opisthosomal trachea II in G. granti extends
Anteriorly,themainlateralopisthosomaltracheaemergeintothe posterodorsallyand,aswiththeanteriorbranch,connectstothe
main posterior prosomal tracheae, thus establishing continuous main lateral opisthosomal trachea and continues dorsally (mo2,
lateral tracheal trunks that extend from the anterior tracheal mlo;Figs.2,3,5,6).Theventralbranchofthemainopisthosomal
anastomosistotheposteriorendoftheopisthosoma.Atthebaseof trachea II in G. granti extends posteriorly, giving rise in each
the main opisthosomal tracheae as well as along their length, segment to small lateral tracheae which extend along the body
smaller tracheae branch off dorsolaterally along the body wall wallbetweenadjacentsegments(mo2;Fig.5).
(Fig. 5), supplying each opisthosomal segment with additional
smallerlateraltracheae. 3.2.5. MainopisthosomaltracheaIII
ThemainopisthosomaltracheaIIIoriginatesfromtheunpaired
3.2.2. MainopisthosomatracheaIandgenitaltracheae stigma on the fifth opisthosomal segment and extends dorsally,
Directlyposteriortotheatrium,themainopisthosomaltracheaI where it bifurcates into two major branches (mo3; Figs. 2, 3, 6)
divides into multiple anterior and a single posterior branches halfwaytotheconnectionofthemainlateralopisthosomaltrachea.
whichextendanteriorlyanddorsally.Thegenitaltracheaoriginates Immediatelypriortotheconnection,thetwobranchesgiveriseto
fromthe anterior branch ofmain opisthosomaltrachea Iandex- additionalsidebranchesbeforetheanteriorbranchconnectstothe
tends anteroventrally, dividing into two major branches before main lateral opisthosomal trachea slightly posterior to the
connectingtothemainlateralopisthosomaltracheaandentering connectionofthemainopisthosomaltracheaIIandthemainlateral
theprosomathroughthediaphragm(g,mlo;Figs.2,3,5).Themain opisthosomaltrachea(mo3,mo2,mlo;Figs.2,3,6).Theposterior
lateralopisthosomaltracheaconnectstothetracheaoflegIVinthe branch also connects to the main lateral opisthosomal trachea
last segment of the prosoma (mlo, g, l4; Figs. 2, 3, 6). The main immediatelyposteriortotheconnectionoftheanteriorbranch.The
lateralopisthosomaltracheathereforeconstitutesthe connection lateral branches of the main opisthosomal trachea III continue
betweenthetrachealnetworksoftheprosomaandopisthosoma. dorsally(mlo,mo3;Figs.2,3,6).
3.2.3. Hearttrachea 3.2.6. Differencesamongthethreespecies
TheposteriorbranchofthemainopisthosomaltracheaIextends The connection of the prosomal tracheal network with the
dorsally,ramifiesbeforeitconnectstothemainlateralopisthoso- opisthosomal tracheal network is similar in G. granti and A. was-
maltracheaandcontinuesaftermakingtheconnection(mo1,mlo; baueri,butdiffersinEremobatessp.(Figs.3,5),inwhichthegenital
Figs.2,3,5,6).Onthesinistralsideofthebody,theposteriorbranch trachea is the sole connection between the prosomal and
446 S.Franz-Guessetal./ArthropodStructure&Development45(2016)440e451
Fig.3. Dorsalviewsof3D-reconstructionsofmajortrachealbranchesofGaleodesgranti(A),Ammotrechulawasbaueri(B)andEremobatessp.(C).Onepairofstigmata(redarrows)is
presentintheprosomaofallthreespeciesalongwithtwopairsofstigmataandasinglestigma(redarrows)intheopisthosoma.Thegeneral,bilateralpatternoftracheaeissimilar
inallthreespecies,butimportantdifferencesaredescribedinthetext.Especiallyprominentaretheairsacsintheanterior,posteriorandlateralcheliceraltracheaeofG.grantiand
A.wasbauerithataremissinginEremobatessp.WhereasthetrachealsupplyoftheheartisprovidedbyonlyonemajorhearttracheainG.granti,twomajortracheaearepresentinA.
wasbaueriandEremobatessp.Abbreviations:ac:anteriorcheliceraltrachea;ap:anteriorpedipalpaltrachea;as:airsac;dp:dorsalprosomaltrachea;g:genitaltrachea;h:heart
trachea;l1el4:legIeIVtracheae;lc:lateralcheliceraltrachea;lp:lateralprosomaltrachea;map:mainanteriorprosomaltrachea;mlo:mainlateralopisthosomaltrachea;
mo1emo3:mainopisthosomaltracheaeIeIII;mpp:mainposteriorprosomaltrachea;pc:posteriorcheliceraltrachea;pg:prosomalgangliontrachea;pp:posteriorpedipalpal
trachea;vp:ventralprosomaltrachea.DisruptionsincourseofmainlateralopisthosomaltracheaofG.grantiareimageandpreservationartifacts.
opisthosomaltrachealnetworks(g;Fig.3).Theheartissuppliedby Thetrachealsupplyof theheartdiffersmarkedlyamongthe
the posterior branch of the main opisthosomal trachea I in A. threespecies:theheartissuppliedbyasingletracheainG.granti,
wasbaueri and Eremobates sp. These tracheae are offset, with the whereasitissuppliedbymultipletracheaeinA.wasbaueriand
branchonthesinistralsideofthebodyextendinganteriorlyandthe Eremobatessp.Theanteriorbranchofmainopisthosomaltrachea
branch on the dextral side extending dorsally (h; Fig. 3B, C). The II does not ramify before connecting to the main lateral opis-
posteriorbranchofthemainopisthosomaltracheaIIsuppliesthe thosomaltracheainA.wasbaueriandEremobatessp.(mo2,mlo;
posterior part of the heart in both species. However, the dextral Fig.3).TheposteriorbranchofthemainopisthosomaltracheaII
branchsuppliestheheartinEremobatessp.,whereasthesinistral continues posteriorly to supply the heart in A. wasbaueri and
branchsuppliestheheartinA.wasbaueri(mo2;Fig.3B,C). Eremobates sp., whereas it connects to the main lateral
S.Franz-Guessetal./ArthropodStructure&Development45(2016)440e451 447
Fig.4. Dorsalviewof3D-reconstructionofmajortrachealbranchesintheprosomaofGaleodesgranti,betweenmid-cheliceraeandlegIII(bluesquare,inset).Redarrowsindicate
locationofprosomalstigmata.Sinistralanddextralanteriorprosomaltracheaeanastomoseinthepedipalpsegment.Theanterior,posteriorandlateralcheliceraltracheaegiverise
toseveralsmallertrachealbranchesenteringthechelicerae.Thedextrallateralprosomaltracheaislesspronouncedthanthesinistrallateralprosomaltrachea,however.Ab-
breviations:ac:anteriorcheliceraltrachea;ap:anteriorpedipalpaltrachea;dp:dorsalprosomaltrachea;l1el4:legIeIVtracheae;lc:lateralcheliceraltrachea;lp:lateralprosomal
trachea;map:mainanteriorprosomaltrachea;mpp:mainposteriorprosomaltrachea;pc:posteriorcheliceraltrachea;pg:prosomalgangliontrachea;pp:posteriorpedipalpal
trachea.AreaswithoutanyvisibleconnectiontopreviouslyreconstructedtracheaeinG.granti,duetoimageandpreservationartifacts,indicatedinpalecyan
Fig.5. Dorsalviewof3D-reconstructionofmajortrachealbranchesintheopisthosomaofGaleodesgranti,segmentsIIIeV(bluesquare).Thepositionsoftheopisthosomalstigmata
areindicatedbyredarrows.Exceptforthehearttracheae,allsidebranchesofthemainopisthosomaltracheaeIeIIIareconnectedtothemainlateralopisthosomaltracheae.The
heartissuppliedbyonehearttrachea.Abbreviations:g:genitaltrachea;h:hearttrachea;l3andl4:legIIIandIVtracheae;mlo:mainlateralopisthosomaltrachea;mo1emo3:main
opisthosomaltracheaIeIII.
Table2
NewlyproposedterminologyformajortracheaeinopisthosomaofSolifugaecomparedwithtraditionalterminologyofKa€stner(1931a).
Newterminology Abbreviation TerminologyofKa€stner(1931a)
Mainlateralopisthosomaltrachea mlo Truncuslongitudinalis
Genitaltrachea g Ramusgenitalis
Hearttrachea h Ramuspericardialis
MainopisthosomaltracheaI mo1 TruncusstigmaticusI
MainopisthosomaltracheaII mo2 TruncusstigmaticusII
MainopisthosomaltracheaIII mo3 TruncusstigmaticusIII
448 S.Franz-Guessetal./ArthropodStructure&Development45(2016)440e451
Fig.6. SchematicdrawingsofthetrachealnetworkofSolifugae,inlateralviewofthedextralside(A)andindorsalview(B),basedonGaleodesgranti.(A)Asterisksindicate
positionsoftheprosomalpairofstigmata,thetwoopisthosomalpairsofstigmataandthesingledistalopisthosomalstigma.Majortrachealbranchessupplytherestofthebody
fromthere.Thedistalendofthemainposteriorprosomaltracheaconnectswiththemainlateralopisthosomaltracheae,creatingananastomosisbetweentheprosomaandthe
opisthosoma.Furtheranastomosesoccurwherethesinistralanddextralsidesconnectattheanteriorendsofthemainanteriorprosomaltracheaandthehearttrachea,andatthe
mainopisthosomaltracheaIII.(B)Thetrachealnetworkisorganizedbilaterallywithoneprosomalandtwoopisthosomalanastomoses.Thetrachealsystemisalsoasymmetric
becauseonlythesidebranchofthemaindextralopisthosomaltracheaIcontinuesintothehearttrachea.Airsacsformprominentstructureswithinthechelicerae.Thetracheaeof
thepedipalpsandthelegsextendallthewayintothetarsi.Overall,thecomplexityofthetrachealnetworkisgreaterintheprosomathanintheopisthosoma.Abbreviations:ac:
anteriorcheliceraltrachea;ap:anteriorpedipalpaltrachea;as:airsac;dp:dorsalprosomaltrachea;g:genitaltrachea;h:hearttrachea;l1el4:legIeIVtracheae;lc:lateral
cheliceraltrachea;lp:lateralprosomaltrachea;map:mainanteriorprosomaltrachea;mlo:mainlateralopisthosomaltrachea;mo1emo3:mainopisthosomaltracheaeIeIII;mpp:
mainposteriorprosomaltrachea;pc:posteriorcheliceraltrachea;pg:prosomalgangliontrachea;pp:posteriorpedipalpaltrachea;vp:ventralprosomaltrachea.
opisthosomal trachea in G. granti (mo2; Fig. 3). The ventral continues posteroventrally to the midgut, parallel to the ventral
branchofmainopisthosomaltracheaIItakesthesamecoursein branchofthemainopisthosomaltracheaIIinA.wasbaueri(mo3,
G.granti,A.wasbaueriandEremobatessp.However,anadditional mlo,mo2;Fig.3).InEremobatessp.,thefirstbifurcationofthemain
branchoftheventralbranchofthemainopisthosomaltracheaII opisthosomaltracheaIIIintotwolateralbranchesoccurssoonafter
connects tothe main lateralopisthosomaltrachea,thus further the main opisthosomal trachea III originates at the stigma (mo3;
interconnecting the opisthosomal tracheal network, in A. was- Fig. 3). The connections of the anterior and the posterior lateral
baueri(mo2,mlo;Fig.3). branchestothemainlateralopisthosomaltracheainEremobatessp.
The ramification of the main opisthosomal trachea III and the aresimilartothoseofG.granti,however.Altogether,theconfigu-
connectionoftheanteriorlateralbranchtothemainlateralopis- rationofthemainopisthosomaltracheaIIIdiffersmarkedlyamong
thosomal trachea in A. wasbaueri resemble those of G. granti. thethreespecies.
However,theposteriorbranchofthemainopisthosomaltracheaIII The results presented here are summarized in Fig. 6 which
does not connect to the main lateral opisthosomal trachea, but presentsschematicillustrationsofthemaintrachealbranchesofG.
S.Franz-Guessetal./ArthropodStructure&Development45(2016)440e451 449
grantiindorsalandlateralviews.Theseillustrationsarepresented tracheaeandensureunobstructedoxygentransporttotheorgans
toaidunderstandingofthecomplexpatternofmajortracheaein theysupply.
Solifugae,andserveasabasisforcomparisoninfuturestudies.G.
grantiwasselectedasrepresentativeintheseillustrationsbecause 4.3. Airsacs
itisthespeciesforwhichwehavethemostcompletedataforthe
entiretrachealsystem. Thelargesttracheaeextendfromtheprosomalstigmataintothe
anteriorpartoftheprosoma,wheretheyformairsacswithinthe
chelicerae (Figs. 2, 3, 6). This previously undocumented feature
4. Discussion
appears to be unique tocamel spiders. The tracheae of tracheate
arachnids are usually thin tubules, which decrease in diameter
4.1. Stigmata
alongtheirlengthandafterbranching(Beier,1931;Woodringand
Galbraith,1976;Ho€feretal.,2000;SchmitzandPerry,2000).The
The stigmata of Solifugae are situated on the prosoma and
largest air sacs were observed in G. granti, the largest of the
opisthosoma. Prosomal stigmata are rare in chelicerates, besides
Solifugae occurring only in Ricinulei and some Acari (Ka€stner, exemplar species studied. The smaller size of the air sacs in A.
wasbaueri and their absence in Eremobates sp. may be related to
1931b), but not in other tracheate arachnids (Bromhall, 1987;
Ho€feretal.,2000; Edwardsetal.,2009).Theunpairedstigmaon their smaller body size and the more slender shape of their
chelicerae. The absence of air sacs in Eremobates may also be
thefifthopisthosomalsegmentisuniquetosolifuges.Stigmataare
explained by the fact that the specimens examined were adult
paired in all other tracheate arachnids. Because the branching
males, the chelicerae of which are highly modified (as in other
patternofthetracheaoriginatingfromtheunpairedstigma(mo3)
membersofthefamilyEremobatidae;Birdetal.,2015).Functional
issimilartothatofthetracheaeoriginatingfromthepairedstig-
interpretationsforthelargeairsacsofG.grantiincludeimproved
mata(mo1,mo2)ofopisthosomalsegmentsIIIandIV,andunder
leverratiosforcheliceralactionduetotheincreasedspacerequired
the assumption of “serial homology” (homomorphy), the single
toaccommodatelargermusculature(VanderMeijdenetal.,2012)
stigmaonthefifthopisthosomalsegmentisprobablyderivedfrom
for subduing prey, i.e., other arthropods like scorpions and even
pairedstigmata(Figs.3,6).Thestigmataonopisthosomalsegments
small lizards (Banta and Marer, 1972). Air sacs also reduce the
IIIandIVaretopographicallysoclosetooneanotherthattheiratria
are separated by only a thin septum (Ka€stner, 1931a) hence the weightoflargechelicerae,whichmayexplainwhytheyaremost
pronounced in G. granti (average body length 55 mm), less pro-
mergerof twostigmata isplausible.Asimilarmechanisticexpla-
nouncedinA.wasbaueri(averagebodylength20mm)andabsent
nationwasalsosuggestedfortheoccurrenceofunpairedstigmata
inEremobatessp.(averagebodylength15mm).Airsacsmightalso
invariousspidertaxa(Levi,1967;Bromhall,1987).Itmaybefurther
function for oxygen-storage or as bellows to enhance tracheal
speculatedthatthemergerofpairedstigmataandpairedtracheae
ventilation, thus playing a role during gas exchange. Solifuges
intoasingleunitmighthaveoccurredduetoareduceddemandfor
displaydiscontinuousgasexchangesimilartoinsects(Lightonand
oxygenintherearpartoftheopisthosoma(whichcontainsmostly
Fielden,1996;Lighton,1998),whereairsacsareknowntofunction
midgut gland and the fecal sac), or in response to the increased likebellows(Chapman,1998;ReshandCarde(cid:2),2009).Inaddition,
efficiencyofgastransportthroughtheextensivetrachealnetwork.
movementsthatmightaidinventilatingairsacsandusingthemfor
A reduction in the number of stigmata reduces water loss, an
air storage, were proposed for solifuges (Nogge, 1976). Such
adaptation to arid conditions (Cloudsley-Thompson,1970; Edney,
movementswouldrepresentanotherpotentialsimilaritytoinsects.
1977;May,1985).
However,nofurtherdataonventilationmovementsinsolifugesare
currentlyavailable.
4.2. Trachealanastomoses
4.4. Opisthosomaltracheae
Thecourseofthetracheaeinsolifugesleadsfromthestigmata
toallregionsofthebody(Figs.2,3,6).Thisisimportantbecause Comparedtothecomplexnetworkoftracheaeintheprosoma,
solifuges lack hemocyanins as an oxygen-carrying protein, and the opisthosoma, which is almost entirely filled with mid-gut
tracheaearethereforerequiredtotransportoxygendirectlytothe diverticula, possesses a rather simple network of major tracheal
tissues. Anastomoses are present anteriorly in the prosoma, be- branchesandnoairsacs(Figs.2e6).Thetrachealnetworkofthe
tween the prosoma and opisthosoma, anteriorly in the opistho- opisthosomaneverthelessdisplaysagreaterdegreeoframification
soma, andin theareaof theunpairedstigma, indicatingthatthe than previously described (Bernard, 1896; Ka€stner, 1931a). The
tracheaeofeachtrachealtreeareinterconnected(Figs.2,3,6).The extent of branching as well as the development of the tracheal
connection between prosoma and opisthosoma comprises two systemwithintheopisthosomavariesgreatlyamongtheAraneae
paired branches in G. granti and Eremobates sp. whereas it com- (Bromhall, 1987; Schmitz and Perry, 2000, 2002) from simple
prises only the genital trachea in A. wasbaueri. Despite this tracheal tubes, e.g., in orb-weaving spiders (Bromhall, 1987), to
apparent difference, the presence of tracheal anastomoses might highlycomplexopisthosomalandprosomaltrachealsystems,e.g.,
increase ventilation efficiency because not only are the prosoma in thewaterspider, Argyronetaaquatica (Crome,1953). Tracheate
and opisthosoma connected but so are the sinistral and dextral arachnids (e.g., harvestmen or mites) exhibit less ramification,
halvesofthebody.Consequently,respiratorygasesaredistributed however, and the tracheal network in the opisthosoma is less
evenlythroughout.Interconnectionsbetweentracheaeareknown pronounced(WoodringandGalbraith,1976;Ho€feretal.,2000).The
inSolifugae,someAcari(WoodringandGalbraith,1976),Opiliones unequal tracheal supply of prosoma and opisthosoma might be
(Ho€feretal.,2000),andinsects(Chapman,1998).Ininsects,how- related tothedistributionofenergy-expensivetissues,i.e., alllo-
ever,anastomosesaremorenumerousthanincheliceratesbecause comotormusculatureandthenervoussystemoccurintheprosoma
everylateraltrachealtreeisconnectedtothetracheaeofadjacent (Klußmann-Fricke and Wirkner, in press). The tracheal branches
bodysegments.Thetracheaeofsolifugesareembeddedwithinthe associated with the heart differ between G. granti, in which the
musculature and organsandthe hemolymph space isreduced to heartisexclusivelysuppliedbyasingletrachea,andA.wasbaueri
small areas surrounding the tracheae. A flexible structure of and Eremobates sp., in which it is supplied by multiple tracheae.
tracheal tubes is therefore necessary to avoid constraining the Another difference among the exemplar species examined is the