Jaktgial Journal t1f'the [.inuan Sr.illl i20(X)i. 129: ]Il 128. \\-ith 2 figures

doi:10.1006/zjls. 1999.02{)9. availalile orlirtc irt http:,//llrr.icle:tlilrran'.com ott lll t }1@

Historical biogeography and ecology of aContinental Antarctic rnite genus, Maudheirnia(Acari, Oribatida): evidence for a Gondwatratrorigin and Pliocene-Pleistocene speciation

DAVIDJ. \IARSHALL*

Department oJ' lookg, Liniuer.rig of Durhan-ll:estuilk P/ Bag x 5100l. Durban 1000,

,\outh Afica

I,OUISH, COETZE,E,

-\ational Museun4 Bloeffintein, South A/i'ica

Receii'cd.januaq, 1999; acupted lor publication '11a1' l9!)!)

Ol thc eieht genr:ra (30 spccics) ol cxtant Acari in Contincntal ( : East) r\ntarctic:r. the genrts

,\Iaudheintia Dalenius & \Vilsorr. I95B (Oribatida; \laudheimiidae) is unicluelv endcrnit:. AGondu'anan origin is proposcd lor thc gcnr.rs b:rsed ot't antiquitr', irrf'erred lrom cndemistn.

a u,idcspread distribution throughout Continental Ant:rrctica and a limited dispersal capacitr'.

Adaptation lor a high montane epilithic eristence. a ncccssitv firr the oligination and lons-tcrm pcl'sistcnce in Antarctica. is inlcrred lrom thc lifc. historr'. pht'siokrgl' and ecolog' olf,Iaudheimia. Phr,logcnetic analvsis placed all four f,laudheitnin spccrics irr a single iecncric) clade

rvith thc follou,ing structure $.L 1et.runia \\Iallu,ork, 1962 ilL tarLngardenensis Coctzee, 1997 0LmarshalLi Coetzec, 1997 (,1/. rr,l/sorrl Dalenius & \\rilson. l95B)))). Gcographical distributionsc:ftht' llaudheintla species. in rclation to tht:ir phvloeenctic rclationships, support the hrpothcsisthat post-(;ondlanan speciation occurred as a {-ronscquence of'isolation cluring elaciation o{'

r\ntarctica.

O 2000 Ihe Linnean Stxietr o1'I-onclou

ADDI'I'IO\,\L KDY \VORI)S: .\cari Antarctica bioecographv cndetnism '\Inudheintia orisin phrloecnr'.

C]ONTE,N'I'S

L'rtroduction\Iatcrial and

DescriptRcsults

methodsion of charactcrs

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DiscussionDispersal potcntial: flaudheitnia con-rparecl to other invertelrratcs

* C.lorresporrding :ruthor.

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E -mail: marshall@pirie.udt.ac.za

lll$31.00/0 O 20(X) Thr Linnean Socictl ol London

D..J. IL\RSHALL AND L. UO|I ZEE

Geographical distribution o[' .l laud heintiu

Ecologr': local distribution and abunclanceFlcoloel': adaptations lbr an cpilithic cristcnce in continental AntarcticzlSpcci:rtion

ConclusionsAcknol lcdgcmcrrtsRel'erences

I\'1'RODLTC]TION

Continental Antarctica supports an impoverished biota. This is iareely the rcsultol demolition of hirbitat ?rnd larsc-scalc spccics crtinction. through slaciation andthe formation ol the East Antarctic ice sheet. The remaining, frcc-livine, tcrrestrialAntarctic launa is represcntcd onh,bv invertebrate phvla (Arthropoda, Tardigrada,Rotilbra, Nematoda and Protozoa). Little is knor.vn about the biogeographical cirigin,ler,'el ol cndemism, or potential for immisration ol most species representing thesephyla (NIarshall & Pueh, 1996;NIclnnes & Pueh, l99B). Biogeographical inlormationlbr the continental Antarctic arthropods is lirnitcd to descriptir.e distribution lists(Dalenius, 1965; Gressitt. 1965; \\iallu'ork, 1973). \{hile dispersal and colonizationare oftcn discussed n'ith resard to thc distribution of the continent's biota (see

\'\,-alton, 1990), little consideration has been gir:cn to their historical isolation.The oribatid mite senus Maudheimia Dalenius & \\'Iilson, l95B (Oribatida; N,Iaud-

heimiidae) is represented in the continent Lrr.- lour spccies: M. u;il,soni Dalcnius &\\i-ilson, 1958, '1L ltetrcnia \{alh.vork, 1.962, II. marshalli Coetzee, 1997 and ,11.

tanngardenensru Coetzee, 1997. Nong u,ith Antarcticoh meyri \{a1lr,r,ork. 1967, thcy arethe onl,v Oribatida cxistcnt in Continental Antarctica. of approrimatelv 7000 knorvnglobal oribatid mite species. The balancc ol thc continent's mites comprises 25species olProstigmata (N'Iarshall & Pugh, 1996). In addition, thc gcnus and famill.(l,Iaudheimia and Nlaudheimiidae) are the onlv supra-spccilic cndcmic acarine taxato the region (Dalenius & \Vilson, 1958; \{allu'ork. 1967; Ohvama & Hiruta, 1995;\{arshall & Pugh, 1996; Coctzee, 1997). AII other genera have maritime and/orsub-Antarctic a{hnitics. Antarcticola me2eri\\ialhvork 1967, lound coastallr- irt wcsternEnderby Land (40"E 50oE; Sugar,vara, Oirvama & Higashi. 1995), has a sisterspccies on South Georgia and Kcrsuelen (sec Pugh, 1993).

I[audheimia \\.as establishcd lcir M. u'ilsoni b1. Dalenius & \"Vilson (1958), and\\i-allu'ork (1962) subsequcntl,v described ,\1. pehonia. The senus rvas initiallr, thoushtto be closely-relatcd to Scheloribales (Schcloribatidac; Dalenius & \\rilson. 1958;\{allrvork, 1973), but thc tlvo gcncra are rcadill'diffcrcntiatcd on octotaric orqans;Maudheimia posscsses porose areas instead of sacculi. Balogh & Balogh (1984, 1992)proposed a ncu,'familv Nfaudheimiidae, rvithin the superfamilv Oripodoidea. Coetzee(1997) recentlvdescrilred'1.L marshaliland).[.tanngardenensis,andsupportedrecognitionof the familv, but moved it to the superlamilv Ceratozetoidea.

Tlris study considcrs tr,vo hypothcses. First, that llaudhelnila existcd in Antarcticaprior to the continent's separation from the rest olGondrvana. Sccond, that spcciationof the cxtant l[audheimia species is post-Gondwanan) resulting fiom isolation, largelvaffectcd bv glaciation ol the continent. 'Ihese hr,potheses are examined using anintesrative approach, r,vhich considers the phvlogeny. bioeeograph,,' and ecologv ofthe Maudheimlc species. In addition to presentins the first phvloeenv lbr an antarctic

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mitc taxon, this is only the second studv presentins evidence for the Gondr.vananorigin ola Continental Antarctic taxon (see Bavll-, 1994).

II,\'I'ERI,\I,,\\D \IETHOI)S

The lour species of l'[audheimia were subjected to phvlogenetic analysis. Specimenslrom nine localities across Antarctica rvere obtaincd, as part ol a rc-cvaluation ofthe genus (Coetzee, 1996, 1997). Nlatcrial included thc type specimens of all fourl[audheimia spccies. Outsroups lverc sclcctcd from thc Oripodoidea and Cerato-zctoidea, putativc superfamilies of ,l[audheimia. Ccratozctoid taxa included the lamilialtype species, Cerato4etes gracilis (N'Iicl'rae1, lBB4), and representatives ol four (of thcfir.e) gcrrera of Sphaerozctinac, Fusco<eter sellnickiHammer, 1952, X[elanoaetes longisetosus

Hammer, 1952, Sphaeroaetes arcticus Harnmer, 1952 and thc Antarctic, Edward4tes

australis Starj' & Block, 1995. The oripodoid spccies sclectcd included the sub-Antarctic Dometorina narionen.si.s Van Plctzen & Kok, 197 1, Qgoribatula subantarctica

Van Pletzen & Kok, 1971 and ScheLoribates.flngellatus\tuallwork, 1966.Character states ol the Maudlrcimia spccics, Qgoribatula subantarctica and Dometorina

marionensi.r, rvere detcrmincd lrom preserved material housed in the acarologycollection of thc National N{useum, Bloemfontein, South Africa. Character stateslor Ceratozetes gracilis, Fuscozetes sellnicki, llelanoaetes longi.retosus, Sphaero3tes arcticus,

Eduardzetes australis and Scheloribates fageLlatus rcfcr to Bchan-Pellctier (1985), Menke(1964), Starf & Block (1995), and \\rallrvork (1966). Three data sets rvere prepared,r'r.ith outsroups beine the Oripodoidea species, the Ceratozetoidea species, and thespecies of both these supcrfamilies. Analyses rvere performed usine PAUP 3.1.1(Su'offord, 1993) r,r,ith the Hcuristic search and Bootstrap options.

Description of characters

1. Rostrum shape: the rostrum is commonly rounded, but often modified de-veloping a medial point or latcral teeth.0:rounded, 1:r,vith medial point.2:rvith lateral teeth.

2. Anterior prodorsal shape: anterior part ol prodorsum may be -nvidc or at-tenuated. Q:prodorsum anteriorl,v attenuated, 1 :prodorsum anteriorly r,vide.

3. Genal tooth: a lateral incision in thc rostral border lormins a free tooth r,vith

r.ariable shape and size (Grandjean, 1952). 0:senal tooth absent, 1:genal toothpointed, 2:eenai tooth truncatc.

4. Shape ol lamellae: thcsc cuticular. dorsal outgrorvths ol thc prodorsum,functionins to protect thc r.vithdrarvn anterior legs (Evans, 1992), are variable inshapeandsize(Trar'6 etaL.,l996i).0:lamellaelormingnarro\{ridges,notprominent,I :lamellae broad, lamellilbrm (blade- or flangc-like).

5. Translamella: the connecting ridge joining the distal ends of the lamellae(Trar'6 et al., 1996). 0:translamella absent, 1 :translamella present.

6. Lamcllar cusps: lamellae mav terminate in a lree, tooth-iike cusp, r'ariable inshape and sizc (Trar.6 et al., 1996). 0:lamellar cusps abscnt, 1:lamellar cuspspresent.

7. Insertion ol lamellar setae: thcse superfamilies usually have lamellar setae

11+ I). J. XI,\RSH.\I_I. AND L. C]OIj]'ZEF,

inserted on thc lamellar apice s or the cusps, rarely on thc prodorsal surface. 0:insertcd orl cusps) l:inserted posteriorlr-to cusps, on prodorsal surfhce.

B. Tutorium: this cuticular outsrou,th. situatcd latcrallr. to (or bencath) thelamellac. like tlie lamellae. protects the distal part ollee I (Grandjean. 1952). It canbe ridgcd or lamellilbrm. 0: tutorium absent. I : tutorium ridgc-shaped. 2 :tutorium Iamclliform.

9. Free cusp o11 tutorium: ll'hen present, the tutorium mav possess a distal, tooth-likc cusp. 0:tutorium abscnt. l:liee cusp abscnt, 2:free cusp prcsent.

10. Shape of'tutorium: hcre reference is madc to the attachmcnt of the tutoriumto the prodorsum, and not the lree standins 'bladc'. This mar.. be short, slightlr.cun.ed and not reacl.ring thc rostral border, or long, semi-circular and reaching therostral bordcr, irrerspcctivc of blade size. 0:tutorium absent, l:tutorium short.slightl,v cur-n'ed. 2 : tr,rtclrium lons. scmi-circular.

I l. Pcdotcctum I: this is a lamelliform outgrowth behind Ies I. directed zrnteriorlr.and protectine the proximal articulations of the lcg (Grandjean, 1952). 0:pe-dotectum I narror,r'. not dorsallv prolonged. | : pedotectum I u,ide, dorsall-v prcilongedtor.vards bothridium.

12. '\i11ar1' saccule: a porosc cuticular inr-agination openine on the infia-capitulum, immcdiatelr, paraxial to thc inscrtion of'the pcdipalp (Norton & Bchan-Peiletier, 1986; Norton et al., 1997). 0:axillary saccule abscnt, l:arillar,v sacculcprcsent.

13. Bothridial scales: sclerotizcd'scales'may be irssociatcd u.ith the usually cup-shaped bothridium (N,Ienke. 1963, 1964: Bchan-Pelletier, 1984, 1985). 0 : bothridialscales absent, 1:bothridial scalcs present.

14. Bothridial openine: althoush usuallv a closcd rounded cup, the bothridiumma,v posscss a latcral opcning.0:bothridium u'ith or r,r'ithout scales, but closed,1 : bothridium r,vith scalcs and lzrteral oper.rinq.

15. Bothridial ccx'cring: thc bothridium mirv be uncovered, partll cor.ered, orcompletely co\.ered bv the antcrior bordcr of the notogastcr or b,v thc anterior edgcsol rhe pteromorphs. 0:bothridium partly covered) 1:bothridiurn completclycovcred.

16. Anterior tcctum; the anterior border olthe notogaster mav hat'e a lree edgeconnecting the ptcromorphs and extending to r.,ar,vine degrees over the posteriorpart ol thc prodorsum. 0: anterior tectum zrbsent, 1 : anterior tectum present.

17. Cuticlc: sclcrotization in oribatid mites is variablc in degree (Alberti. Storch& Renner, 1981;Pugh, King & lordr', l987). 0:r.vell sclerotizcd, hard cuticle, 1:u,eakly sclerotized, leathery cuticlc.

1B 20. The notosastral setae, d7, c3 &nd thc d-scrie s are of phylogenetic importancc(Grandjean. 1949; Seniczak. Behan-Pelletier & Solhor', 1990: Trar,6 et al.. 1996).Primitil'el-v. all these setae are present, r.vith loss occurrins in dcrivcd forms. 18. 0 :seta c/ present, l:seta c7 absent; 19. 0:seta ca present, 1:seta.r absent; 20.0:1-series present, I : d-serics absent.

21. Octotaxic organs: in clribatid nritcs the octotaxic s,vstem comprises con-centrations ol pores in the cuticle, knou.n as porosc areas. These ma) becomcinvaginated lorming sacculi (Norton et al., 1997). Q:porosc areas, 1 : sacculi.

22. Stzc- of octcltaxic organs: 0: octotaric organs not minutc, I : octotaxic organsminutc.

23. Lernticulus: a distinct. unpaired. transparent area lvithin thc cuticle, Iocatedantero-dorsalll. cln thi: notogastcrr. It is a secondarill' devclopcd photorccrcptor organ

(;O){D\|-\NAN OR]C}I\' IIOR .\I,1|-DHEI,\IL1 1I:I

(Alberti & Fernandcz, 1990; Nberti. Kaiscr & Fernandez, 1991). 0:lcnticulusabsent, 1 :lenticulus prcscl1t.

24. Postanal porosc area: an unpaircd porose areal posterodorsal to the analplates. and slightlr.. removcd lrom the circumsastric scissure (Norton et al., 1997'5.

This diffcrs iiom the marginoventral scrics of porose areas rvhich ibrm a narrowband adjacent to thc solt cuticle of the circumgastric scissure. These smal1 porose

areas may fi.rse to form a narro\\r ribbon ol porositv. as in Jgorihalzla, u.hich is nothomolosous to the postanal porose area (Grobler. 1993: Norton et al., 1997).0:postanal porose arca allsent, 1:postanal porose area present.

25, 26. Shape and size olpterromorphs: cuticr,ilar, anterolateral outgrou'ths olthenotogaster lorming u,ins-like erpansions lor protection olthe legs. Primitir,clv. smalland horizontal. becomine largc and r,'entralh' cun,scl in the more dcrirted Iorms.Ultimatcil. are hinged. permittine mo\rcment (\Voodring, 1962; Evans, 1992). 25.

Pteromorph shape. 0:short, horizontal, 1 :Iong, curved vcntralll'; 26. Ptcromorphorientation and size. 0: antcrolateral corncrs directed posteriorlv, ptcromorphssmall. I : anterolateral corncrs dircctcd anteriorlr'. pteromorphs largc.

27. Sejugal apodeme: internal. transverse laminae (or ertensions) of the anteriorand posterior borders of each podosomal segment (: cpimeres, see 2B). The apodeme

bctu'een epimeres II and III is the se.jugal apodcmc. Apodemes arc not formedsecondarilv. but rather are lost during the course ol evolution (Grandjean, 1952:

Er.ans, 1992). 0:se.jugal apodeme continuous, 1:sejugal apodeme reduccd.28. Numbcr ol setac on epimcrc III: epimeres lbrm from the croskeleton

surrounding the acetabula and ertend medialll' @araxiallv). Thc,v represent po-dosomal segmcnts. Therc is ontogcnetic r-ariation in epirneral setae, \\.ith thosc setae

appcaring in the later ontogenetic stages (3, and 4) being more susceptible toer,olutionarv loss (Grandjean. 193't). 0:seta 3, present on cpimere III, l:seta 3,

absent on epimere III.29. Custodium: a pointed. cuticular proccss, attached to the bod,v in thc vicinitv

of leg III and alu,avs dirccted antcriori\'(Grandjean. 1952). 0:custodium absent.

1:custodium present.30. Number of' setae on genital plates: senital setal numbcr is an important

taronomic character in oribatid rnites. Adults ol l'rip;her oribatid rnites nominallyhave six pairs (Grandjean. 1949). 0:6 setae on each genital plate, 1:4 setac oneach genital platc.

31. Size ol genital piates in females: 0: fcmale genital plates smaller or equal toanal plates, I :female gcnital platcs lareer than anal plates.

32. Pre-anal orean (shape): An internal porose orsan associated u.ith thc prc-anal scleritc, lies anteriorlr- of'the anal openirrs. The ano-gcnital muscles orisinatelrom this organ (Norton et al., 1997). u'hich is variable in shape and sizc. 0:stemof pre-anal orp;an short arnd u,idc. 1 : stem of pre-anal organ lone and narrou'.

33. Ventral carinac on femurs: lamellilorm cuticular outgrou'ths on the ventralsidcs ol all or somc of the fcmurs, lor protection ol thc legs. 0:r'cntral carinacabsent or small and insignificant. l:\'cntrzll carittac present, broad, promincnt.

3rl. Solcr-ridion 1 on tarsus I: the 'normal' position lbr this solenidion is near 2and the famulus, and it usually lorms part of the tarsal cluster (Grandjcan. 1935;

Norton, 1977). Distal displaccment to\\rards the tectal setae is unusual (Behan-

Pelleticr. 1985). l):insertcd near solcnidion 2 and famulus, 1:displaccd distallv tor-icinitr. ol tectal setae.

35. Number olsetae on ibmur III: r'crv olten tirerc arc 3 setae on fctnur III. r'iz.

116 D..J. \IARSH,\LL ,\\D L. CtOItTZFtL

d (dorsal), /' (antiaxial lateral) and z,' (antiaxial ventral) (Trar'6 et a\., 1996). The lossolseta /'has been rcported in somc ccratozetid specics (Behan-Pelletier, l986).0:seta /'present (3 setac), l:seta /'absent (2 setae).

36. Shapc of antiaxial ventral sctac /," on tibia I and II: normallr.' these sctae aresetiform and sirnilar to thc other les'setae. but mav also bc spinous. thickened anddistall,v tapered (Behan-Peiletier. 1986).0:setae 2," on tibia I and II not spinous,1 : setae r," on tibia I and II spinous.

37. Length olantiaxial lastigial scralfi" on tarsus I: thc fastigial setae (fi) occurdorsally on the tarsus. usuallv ncar thc solcnidia I and 2 (Grandjcan. 1940; Norton,1977: Trar'6 et al., \996).0:setaft" morc or less the same Iensth as jft',I:scta_ft"much shorter and thinner thanJi'.

38. Humeral orsan: a porose orsan. usualh. papillifbrm. sometimes present inimmatures, and situated just behind the sejugal furrolr. and antero-latcral to seta cr.

The orsan ma1'form a porosc disk-likc sclerite (Grand.jean, l95l; Norton et al.,1997). 0 : humeral organ absent. I : humeral organ papilliform, 2 : humeral organa porose disk.

39. Humcral sclcritc bcaring gastronotal seta .1: a subtriangular. micropr-rnctatescleritc carrving seta .1) situatcd in the humeral resion olimmatures (Behan-Pellctier.1985, l986). 0:humeral sclcrite absent. 1:humeral sclerite present.

40. Gastronotarl porose sclerites: thc sastronotal arca of higher oribatid mitcimmature stages commonly hzrve porose sclcritcs (areas) in various forms ,,'iz.

microsclerites bcaring (or rvithout) eastronotal setae (excentrosclerites), or ma-crosclerites bcaring gastronotal setae, or a mixture olthcsc lorms (Grandjean, 1953,1963, 1970;Bchan-Pclictier, l9B4;Norton et a1.,1997).0:microsclcrites rvith setae.I :macrosclcritcs alone, or i.vith microsclerites not associatcd r'l'ith setae, 2:macro-and microsclerites assocriated u..ith setac.

1TE,SUI,1-S

The analvsis using onlv the oripodoid genera as the outgroup shor'r'cd 3l characterscommon to Maudheimiaancl thc outgroup species (Table 1). Three trees are retained,and thc bootstrap 50% rnajoritv-rulc conscnsus trce consisted of 40 steps, lr'ith aconsistency index of'0.8, and a homoplasv indcx of 0.2. Topolog-v of'the insroup is thcsame as that lr.hen usine both superlamilies (Fig. l), and thc out€iroup is unrcsolved. Abootstrap value ol 100 is attained lor the branch leading to the ingroup.

The analysis using thc ccrozetoid gcnera as outgroups, shorved 29 commoncharacters (Tablc 1). One trcc is rctaincd, and thc bootstrap 50% majority-ruleconsensus trcc consists of 36 stcps, rvith a consistency inder ol 0.806 and homoplasvindex ol 0.194. Again the topolow of the ingroup is the samc as the tree in Fisurel, but the outgroups S. arctius and -E austrahs are slvitchcd and the trec is fullyresolvcd. A bootstrap value ol 100 is attained for the branch ieadine to the ineroup.

The analvsis including the species lrom both the superfamilies, includes all 40characters (Fig. 1; Table 1). Onc trcc is retaincd. The length olthe bootstrap 50%majoritv-rule consensus tree is 66, the consistenc,v indcr 0.712, and thc homoplasyindex 0.288. Tiie bootstrap value of'the branch leading to thc Oripodoidca outgroupis 100, to the Ceratozetoidea outsroup is 98 and to thc ingroup (llaudheimtn) is 99.

The pht,logenetic anah,sis indicates that Maudheimia is a monophr-lctic sroup)

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Figure 1. Cladoeram depicting hrpothesis fcr the evolutictt ol f,Iaudheizela species. (Q) state 0; (f)statc 1;(I) state 2. Thc charactcr states on thc tcrminal branchcs are indicatcd bv letters as follow's:A:lB, 19,20; B:25; C:35; D:5, 19,33,39: E:1r F:23.24.36; t;:19,20; H:3; l:5, lB;.J:33; K:1; L:28,35: \{:25; N:l; O:,1,33; P:2Br q:15, 19,20,27,37; R:5; S:21.

Bootstrap l'alues arc indicated in rectangles.

separated from the other ceratozetoid senera by I I synapomolphies, namely, alvide, rounded prodorsu- (2), ridged lamellac (4). ridged rurorium (B), absence ofthe lree cusp on tutorium (9), Iatcral openins of bothridium (14), weakly sclerotizedcuticle (17), minute octotaxic porose arcas (22), extraordinary large gcnital openingof females (31), absence of lemoral carinae (33). disk-shaped humeral organ inimmatures (38) and the presence of macro- and seta-bearing microsclerites inimmatures (40). Nfost of these attributcs indicate a reduction in size or loss ofstructure) particularly thosc rcferrins to thc lamellae, tutoria, tutorial cusp, femoralcarinae and sclerotizarion ol the cuticle.

The loss of seta -1 'on fcmur III (charactcr 35) of ,4.L petronia is an autapomorphyfor the species, but also occurs in E. austraLil The insertion of the lamellar seta(character 7), posteriorly to lamellar apex, is a synapomorphy for M. tanngardenensis,

M. marshalli and L[. wil.soni. The short horizontal pteromorphs (character 25) of M.tanngardenenszi, and the presence ofsetae c, r, and d-series (characters 18, 19 and 20)in M. marshalli, both represent autapomoryhies for these species respectivelv andreversal to the primitive state. The long semi-circular shapc of the tutorium is asynapomorphy lor M. marshallt and M. u,iLsoni.

DISCUSSION

Dispersal potentjal: Maudheimia compared to other intertebrates

Geographic distribution is the result oldispersal or vicariance) or some combinationof the two (N,{yers & Giller, l9BB). Where dispersal is considered to be prominent

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(]OND\I.\N,\N ORI(]I)i FOR ,\I..IL.'DHF:1,\IIA 119

in distribution, this should be apparent from thc biota's potential for dispersal, its

dispersal rnechanism, and the distribution pattcn-r itself, notu'ithstandins otherfbatures such as the capacitv lor re-colonization. \{ind may be the most importantdispersal agcnt ol Continental Antarctic microbiota (see \Valton, 1990; Seppelt.

1995; Broad1., 1996). \\hereas both man and birds ma-v currcntl.v affect limitcddispersal of invertcbrates in the continental region, thev cannot be consideredprimarv dispersal agents. N{anv Antarctic plants and inr.ertebrates have el'olvedpropagules suitable Ibr lr,ind dispcrsal (see Ellis-Evans & \{alton. 1990; \Valton,1990). The efficzrcv ol thcsc depends on attributcs of size (fbr crample. Icss tharr

100pm), rveight, abundance of-production (Ibr example, thousands per lifecvcle;\{alton. 1990) and, phl,siolouical rcsistance to lou' temperature and dcsiccation.Thc major terrestrial Antarctic inr.crtcbrate phr'la (Protozoa, Nematoda, Rotileraand Tardierada), r,r'ith thc exception of the Arthropoda, har,e propagulcs conlormingto this general trend.

Nfanv Antarctic inr,'ertebratcs, excluding arthropods, are anhvdrcibiotic and/orcrr,ptobiotic, nhich enhanccs their dispcrsal capacitv. The arthropods (includingtrIaudheimia) are not ph,vsiologically cquipped lbr present-day aerial dispersal across

the continent. In contrast to rotifcrs, tardigradcs and nematodes, r'r'hich colonizeupon settling in far..ourable habitat, Antarctic arthrop<-ids behaviourall,v select habitatro match their relativelv moderate phr.siological capabilitics. The lile historl' char-acteristics of llaudheirnrz further constrain dispersal. These includc lor,v ibcundit-v

(tlvo to four eggs per lemale per fil'c-year period), crompact juvcnile aggregations,

and the cementation of eggs to surlaces (Nfarshall & Convcy, 1999). Thc elficaclof rotilcr and tardigradc Antarctic dispersal is suggested by the circumpolar dis-

tribution olsome specics (see NlarshalI et a\.,1995b; Nlclnncs & Pueh, 1998). \Niththe exception of lanorche.rtes antarcticzr Strandtmann, 1963 (Prostigmata), arthropodsdo not shor,r,circumpolar distributions (l{ise & Gressitt, 1965; Pugh' 1993; Green-

slade, 1995;Judson, 1995; Frati et al., 1997; Con-n-ey, Greenslade & Pueh,2000).

Chograp hical dis tribution o/ Nlaudheimia

Collectiveiy, l'Iaudheimia is circumpolarl,v distributed in Antarctica (Fig. 2; Table2). It ranges lrom Victoria [,and (170"E), to the Ahlmannr)-sgen (10"\\) in r'r'estern

Dronning Nfaud Land; ,l,L l1etrottia beine thc sole species in Victoria Land(170 160'E), rvith the others occurrins in Dronning N'faud Land (DNIL; 10'\\L30'E). The Maudhelrzia species exhibit non-overlapping, allopatric distributions: ,1L

u,ilsoni is restricted to thc Ahlmannryggen range, l'1. marshalli extends across the HUSverdrupfiella, the Gjelsvikfiella and the Nftrhlig-Hoffmanf ella, and '1L tanngardenensis

occurs on Tanngarden, a western nunatak olthe Sor-Rondanc range (Fig. 2, l'ablc2). Distributions of the DN,IL species arc delimited bv threc laree glaciers (sec Fig.

2): the Jutelstraumen, betr,vectr the AhlmannrYggen and the HU Sverdruplellaranges, thc H.E. Hansenbreen glacier, at the western border ol thc Sor-Rondanerangc, and thc Bvrdbrcen glacier at the eastern border of this range. Separation olthe DN'IL species tlpifies a barrier effect by these glaciers.

Disjunction in the contincntal distribution of trIaudheimla in DNfL and VictoriaLand is the likely result of these rcgions being isolated during extensive glaciationof the eastern Antarctic scctors, Enderb,v and \\iilkes (30 150'E; see Goodrvin, 1993;

rhe present dav oases at Vestibld Hills, Bungcr Hills and \{indmiil Islands lvere

D. J. \[,\RSHALL AND L. COE',I'ZEF]

Figure 2. A, continental distributions of thc ;llaudheimla spccics: tr[. ruilsoni (\hv), ,l.L mar.s:halli (NIm),M. tanngardenenrzi (NIt) and 11. petronia (NIp). B, mountain ranges (A) in Dronning Nlaud Land on rvhichthe,l4audheimia species are found, and prominent glaciers (x)in the rcgion: Ahlmannngeen (Ali),Jutelstraumen (Ju), H.U. Sverdrupfella, G.jclsvikfella and \,Iuhlig-Hoffmannlella (SGNI), H.-E.

Hansenbreen (Hai, Sor-Rrxrdane (SR), B,vrdbreen (B1).

completely covered during the last glacial maxima, 1 I 000 ya; Ingolfsson et al., lgg9).Low acarine diversities and disharmonic, poorly-associated faunas further reflect theelaciation extent of these sectors. The number of free-living acarine species in IVIaud,Scott, Enderby and Wilkes sectors (re: Puuh, 1993), as a percentage of the total is,respectively,2To/o,5lo/o, llo/o and B%. Furthermore, Enderby and Wilkes showzero association with the maritime,/continental Antarctic acarofauna, even at thefamily level (N.{arshall & Pugh, 1996), suggestins colonization from the sub-Antarctic.The region below the polar plateau in the Byrd and Ronne sectors to the r,vestremains heavily glaciated due to its close polar prorimity, currently isolating 'u.estern'Antarctica. Intracontinental dispersal of most acarine specics probably ceased at the

;{fr ^i:tJu

I ""I^^{{SR}

GOND\\'ANAN ORIGIN FOIP. ],IA UD H E I,\1 L4

Teern 2. Records of Maudheimia in continental Antarctica

121

Species Regions/localities Relbrence articles

l.L uilsani

tr[. marshalli

lI. tanngailenesi

)1. petrunia

Dronning Nlaud LandAhlnannrygqen:

Passat/Boreas (7 l"l8'S, 01'03'\\J

Robertskollen group (71'28'S. 03"15'\\)

Straumsnutane (7 I "3tj'S. 0l "'17'\\)Johnsbrotet (7 1'20'S, 01'10'\\1H.Li. Swdrul:falkt: (72 73"S,0'30'\'\' 0l "30'E)VendeholtenRomlin.gane, Tua, Brekkcrista,'I'r'oraQelsililjella:

.futclsessen (72'03'S, 02'10'E))Iiih lig H of nan 4[ e I la:

Plogskaltet (7 1'50'S, 05'1 5'E)Svarthamaren (7 I "55'S, 05'10'E)Ekberget ( :.Jutulrdrir)Sor Rondane: (72'S, 22' 28'D)T:rnnsarden (72'S, 23'E)Victoria LandHallct Glacicr (72'S. 170"E)

Redcastle Ridge

Dalenius & \{ilson (1958), Gresitt (1965),Dalenius (1965), Cressitt & Shoup (1967),\{alhvork (1967, 1973), Cloetzce (1997)Ryan el a/. (1989). Ryan & Watkirx (1989),Nlarshall e1 al (1995a)r, Coetzee (1997)(DJNI. pers. obs.)(DJNI, pers. obs.)

Srimme (1986)!, Somme sl aL (1993)Somme (1986)'], Coetzee (1997)

Somrne (1986)'!, Coetzee (1997)

Coetzee (1 997)CocLzee (1997)Dalenius & \\'ilson ( l 9iB) (scc Coetzce, 1 997)

Ohvama & Hiruta (1995), Coetzec (1997)

Walhvork (1962), Coetzee (1997), Gressitt(1965), ()ressitt & Shoup (1967)Coetzee (1997)

rNlarshall et al. (.1995a:1 incorrectlv refer torIn all papers prior to Coetzee (1997),

'1L

l[. dboni as l[. petronia.

mar.shalli is given as lI. utilsant

onset of the Pliocene-Pleistocene glaciation, suggesting that the widespread dis-tribution of Maudheimia indicates its antiquity to the continent, and at least a pre-Pliocene continental existence.

Ecolog: local distributiln and abundance

Maudheimia is vertically distributed in Continental Antarctica over a range ofaltitudes, from low nunataks (c. 200 m altitude) to the mountain peaks (r. 2000 m)(Table 2). Antarctic altitudes were much greater prior to the ice sheet development(Pliocene-Pleistocene), u'hich currently depresses the continental plate. Nunataks aremore likely to be inundated by ice than are the higher mountain peaks. Numerousfactors must influence the occurence of Maudheimia at nunataks. Its absence fromlow altitudinal and high latitudinal nunataks in the Ahlmannryggen (DJM, pers.obserr..) suggest these to include minimum temperature, water availability, and long-term (geoloeical) frequency,/extent of potential ice scour events.

In an assessment of r,r,ithin-nunatak abundance variation of M. wilsoni (determinedat Ice Axe Peak, Robertskollen (7 io2B'S, 3o15'E), Ahlmannryggen, western DronningMaud Land), the effects of aspect, heieht and proximity to a bird colony wereconsidered (see Ryan et a1.,7989 and Ryan & Watkins, 1989, for descriptions of thehabitat and biota at Robertskollen). Density at the summit (250 individuals/O.25 m2

or 1000 individuals/m2) was vastly greater than elsewhere on the nunatak (less than

t22 D. J.

'Ihnrn 3. Density (indir.iduals per

\TARSHAI,I, I\ND L. COE'I'ZTO

0.25 m':) ol llaudheimia ui/soni at Ice Axe Peak, Robertskollcn

Nlcan* 1 SD (r:20) Probalrilin' iP laluel

Sitc 2 Site 3 Site {

Sitc I

Site 2Site 3

Site .l

20. l5 + 16.3.1

250.15+180.026+.65 + 9.t.8520.95 + 48.70

0.(xx) 0.1 13

0.(xl0

( ).( x)80.(xx)0.005

Sampling u,as undertakcn zrt Ibur sites (approximatelv 500 rn' each) olvarving orient:rtion. rtrtical position. alrJproximitl' to bird colonl., on the nunatak Ict- Axc Peak. l{obertskollen (altitude +80 m), Ahlmanun-ggen, f)ronnirgNlaud Land: site (lI sumrnit above a bird colonv, site (2) north east slope u'ithitr tr bircl colonr', site (3) llat trrea

belorv the north cast slope, and site (.1) u,est slopc rvithin a bird colon1,. For e:rch site. t\\'enn'rattdomiv seleclcdice-sorted poll'gons rverc sampled. Densitv u,as determined b1' coutttinr mitcs rurdcr thc stones of rhe pollgonnithin a 0.25m2 quadrat. Thc probabilitr, ol'densitv being signi{icantlv dillbrcnt. at diffcrcnl sites nas cletermitredusinq a \Iann Whitnel' U-test.

Tesl-n 4. Association ol' tllaudheinria u;ilsoni t;ith three plant species

Pcarson's r cocflicicnt Probahilitr, lP-r'ahrer

U.tnea nntantica

Llmbilicaia detussala

Bn-ophltc

0..16560.83010.0391

0.(xx)t).00t)0.731

Sec Table 3 lbr sampling procedurc. Ilitc dcnsitv lor thc lJO quadrats u.as compared rvith the coler ol theprominent ljc.hens (lmhiLicaria detu.tsata, Usnea antantica and an uniclentified br-r'ophvtc, in thc sarne quadrats. Ciorerrvas asscssed by using a 49 squared grid (approximatell 900 cmr).

70 individuals/0.25 m2 or 280 individuals/m2; Table 3). These data suggest greaterinstability of habitat on the slopes, probably due to a greater frequency ol ice scourover geological time, and the poor capacity of Maudheimia lor recolonization on thcnunatak. Stability of the summit habitat would also explain the greater cover thcreof Lrmbilicaria decussata, the lichen lavoured by Maudheimrz (Table 4).

Ecologlt: adaptations for an epilithic existence in confinental Antantica

The nunataks and mountains of Continental Antarctica are characterized bychalicosystems: habitats of lithosol, gravcl or rock (Janetschek, 1963). Spccializationlor an epilithic (rock) existence is seen in the morphologv, physiology, life historyand leeding of Maudheimla. Although Maudheimia is found in association with thealga Prasiola crispa (DJM, pers. obsen'.), it is primarily lichenivorous (\\rallwork, 1962;Dalenius, 1965; Gressitt, 1965; Gressit & Shoup, 1967; Seyd & Sear,vard, 1984;Ohyama & Hiruta, 1995). Prasiola grows in ornithogenically-enriched habitat patchcson the nunataks and is a relatively reccnt Continental Antarctic inhabitant (theearliest record of bird presence at Antarctic nunataks is c. 35 000,va; Hrller et al.,

19BB). It is probable that prior to this, Maudheimia had an association with epilithiclichens only, to some extent corroborated by high densities of Mlaudheimrz amongstlichens (u-mbilicaia decussata and Lisnea antarctica) as opposed to bryophvtes (Table 4).

Little is known about the origins of lichens in Continental Antarctica (Seppelt, 1995),

limiting further support ol the Maudheimia-lichen historical association. No other

(IOND\\IANAN ()RIC;IN FOF. ,\I'ILtDHEI:IIIA 123

acarine species found in DN'IL is, howerrer, knorvn to live or feed on lichens (DJM,pers. observ.).

Aspects of the phvsiology of A.[audheimz support epilithic adaptation. Summerrock habitat temperature fluctuates diurnally, often reachins upper temperatures ol30'C (N{arshall et al., 1995a). Maudheimia wilsoni increases physioloeical rate linearlyrvith temperature, over the entire range of positivc temperatures it experiences(N{arshall et al., 1995a). Rate is accelerated more rapidly than in sub-Antarcticoribatid mitcs, r,r'hich arc not normally cxposed to similar high temperatures (Marshall& Chown, 1995). This presumably maximizes leeding by Maudheimra during theshort summers characterizing Continental Antarctica (N.'Iarshall et al., 1995a). Maud-heimia alsct has a higher desiccation tolerance than its sub-Antarctic counterparts,rvhich are naturally exposed to wetter conditions (NIarshall, 1996). Its relativelv poorsubmergence toleranie argues against a lor,l4and, sub- or maritime Antarctic orisin(N{arshall, 1996).

The formation olcompact multi-instar aggregations under stones, and thc adhesionof eggs to rock surfaces, are other possible epilithic adaptations ol f,'Iaudheimia(N,Iarshall & Convey, 1999). Long gcneration times (up to 5 vears to mature) andthe lorv lecundity (two to four large eggs per lemale lifespan) of Maudheimla (N,farshall& Convey, 1999) are consistcnt with an existence in adverse, but stable habitats(Greenslade, l9B3; Convey, 1996), and imply a potentially slor,r' evolutionarv rate.While rapid evolution vvould be unnecessary in an abiotically stable environmentdevoid of parasites, predators, and competitors, benefit is potentially eained frompreserving a senoqpe suitable for the prevailing Antarctic adversity (Greenslade,l983; Convey, 1996).

Nthough the female genital openings of Maudheimia and its Continental Antarcticcounterpart, Antarcticola meyri (Sugawara et al., 1995), are rclatively largc (presumablyrelating to their large eggs), the distinctive characters separating Maudheimia fromthe outgroups show reduction in size or loss ol structures (see Result$. Smallstructures of Maudheimia putatively relate to an epilithic habitat (as opposed to anedaphic habitat), which also lacks predators. (The only knor'r'n predatory miteoccurring in Continental Antarctica is the prostigmatid rnite Coccorhagidia gressitti

Womersley & Strandtmann (see N'Iarshall & Pugh, 1996), and it is not known tolced on or live in the same regions as A'[audlteinia). Thick cuticles and largeintegumental structures in oribatid mites are thought to provide protection from therigours olsoil abrasion and/or predation (Alberti et al., l9B1; Schmid, 19BB).

Speciation

Glaciation of Antarctica commenced during the late Eocene (c.45 mya; Clarke& Cramme, 1992). Since then the continent has experienced extreme temperaturefluctuations. The most severe glaciation event leading to the formation of the EastAntarctic ice sheet r'vas lairly recent (Pliocene-Pleistocene; Clarke & Cramme, 1992).Though this cvcnt had the sreatest effect of obliterating the Antarctic biotas andisolating populations, temperate valley glaciers could have been prominent duringthe earliest of elaciations (Clarke & Cramme, 1992). In any event, the most Iikelysurr,'ivors rvere the high montane species llke Maudheimia, which escaped ice coverand rvere pre-adapted for cxtremely low temperatures.

Antarctic distributions of the Maudheimia specics strongly support speciation

t21 D.J. \TARSHALT, A\D r.. COETZEE

resulting from glaciation-induced isolation of populations (Fig. 2). The basal species,M. petronia, is isolated from the DML specics, r,vhich arc themselr-es isolated fromeach other in a phylogenetic pattern consistent with Pliocene-Pleistocene slaciationpatterns (Fig. 1). Ilspeciation were pre-glacial, numcrous other distribution patternsfor the species could have emerped, the most extreme case being a random pattern.

Speciation mediated by glaciation is further supported by the circumlerentiallyanticlockwise sequence of cvents producing the lour species ol l,Iaudheimia, frotnVictoria Land, across East Antarctica to DN'IL. This conforms to a directionalconstraint as suggested by a theoretical model for thc development of the EastAntarctic ice sheet (N{archant et al., 1993). \\rarminq leads to ice sheet recession,exposing a rocky corridor along the coastal edge ol the continent. Ihe oppositeeffect, resulting from cooling, would have isolated populations along this corridor,as inhabitable space was reduced. Had pre-glacial speciation occurred, the scquencesand directions of speciation would not have been expected to correspond to thisparticular pattern across the ertent of the contine nt.

Our data do not permit speculation on previous geographical ranses of theputative common ancestors ol Maudheimia species. Neither can we determine u"ithany robustness whether the actual process ol isolation occurred by peripheralisolation (sequential or otherwise) or vicariance (\\'iley, 1981; Wilev & N{avden,l9B5; Funk & Brooks, 1990; Brooks & N{clennan, 1991, 1993). It should also berealized that simultaneous development ol isolation barriers (icc shcet development)separating the DNIL species in particular, could have effected polychotomousspeciation.

CONCI,USIONS

The antiquity of l,tlaudheimia in continental Antarctica is indicated by its restrictionto the continent, and its widespread distribution across the continent in the light ofa poor capacitv for dispersal. The K- or A-selected lile history attributes, Iichenivory,temperature-dependent physiology and summit-concentrated local distributions, allsuggest adaptation for a high montane, epilithic existence. This r,vould be essentialfor the continued survival of the extreme climatic changes that Antarctica has

undergone. The above support the existence of Maudheimia, prior to the finalseparation of Gondwana and the glaciation ol Antarctica. The closest relatives olMaudheimia, therefore, may be expected to occur in mountainous regions ol theother Gondwanan fragments, rather than in the sub,/maritime Antarctic regions.Though the genus appears to have resided in Antarcticafor a substantial period oftime, the sequence of speciation events producing the four known extant species olMaudheimia indicates speciation occurring after the onset of glaciation (late Eoccne),probably during the most recent glaciation event (Pliocene-Plcistocene).

Hoberg (1992, 1995 also Hoberg & Adams, 1992) recently presented phyioeeneticand biogeographical evidence supporting the hypothesis that speciation involvingseveral invertebrate parasite taxa occurrcd during the Pliocene-Pleistocene glaciationperiod in the Arctic. This sccnario, dubbed the Boreal Refugium Hlpothesis (see

also Brooks & Mclennan, 1993), is remarkably similar to the one we propose hereinto explain evolution in Maudheimz. This study may therelore suggest that simiiarevolutionary dynamics, speciation as u'ell as extinction, were operating in bothboreal regions of the planet durins the Pliocene-Pleistocene period.

125

.\C]K\O\\II,ED(}ENIENTS

Daniel R. Brookes (Universitv of Toronto, Canada), Roy Norton (State UnivcrsityolNerv York, U.S.A.), Valerie Behan-Pcllctier (Agriculture and Agri-Food Canada,Canada), Ster.'cn L. Chor'r,n (University ol Pretoria, South Africa), Kcvin J. Gaston(University of Sheffield, U.K.), PhilipJ.A. Pugh (British Antarctic Survey, U.K.) andPcnelopc Grcenslade (CSIRO, Australia) are thanked for advice concerning thcphylogenetic anal1'sis and/or criticallv commentins on earlier versions of this paper.DJ.\,I acknou,ledses PhilipJ.A. Pugh lor stimulating ideas on the topic in an earliercollaboration.JohanJ. Spics (University of the Oranee Free State, South Africa) is

thanked lor thc use ol thc PAUP 3.1.1 programme and computer equipment.Lennart Cederholm (University of Lund, Srveden) and Sabina Sr.vift (Bishop N{useum,

Harvaii, U.S.A.) provided the trpe material of M. wikoni and rM. petronia, respectively.

Jan E. Crafford helped rvith the fieldrvork at Robertskollen, Antarctica, in 1992/3,u'hen DJ.N,{. rvas under the employmcnt ol the FitzPatrick Institute, University ofCape'I'own, South Africa. The South Alrican Department of Environmental Affairsand f'ourism pror.'idcd logistical and financial support through the South AlricanCommittee lor Antarctic Research.

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