1492

COVE. The crustose lichen L&eanora disperss. lichen sym­bioses, associations between fungi and algae, have originated multiple times during fungal evolution. At least one successful establishment of symbiosis led to the more than 6000 species of the order l ecanorales,

represented here by L. dispersa. The white-rimmed cups (between 0.3 and 0.7 millimeter in diameter) emerging from the rock substrate produce the meiotic spores of th is fungal symbiont. See page 1492 and the News story on page 1437. IPhoto: V. Wirth]

Multiple Origins of Lichen Symbioses in Fungi Suggested by SSU rONA Phylogeny

Andrea Gargas; Paula T. DePriest , Martin Grube, Anders Tehler

Phylogenetic hypotheses provide a context for examining the evolution of heterotrophic lifestyles. The lichen lifestyle, which is the symbiotic association of fungi with algae, is found in varIous representatives of Dicaryomycotina, both Ascomycetes and Basidio­mycetes. A highly resolved parsimony analysis of small subunit ribosomal DNA (SSU rONA) sequences suggests at least five Independent origins of the lichen habit in disparate groups of Ascomycetes and Basidiomycetes. Because lichen associations arose from parasitic, mycDfThizal. or free-living saprobic fungi, neither mutualism nor parasitism should be construed as endpoints in symbiont evolution.

L ichens are a classic example o( symbiosis ["Zusammenleben ungleichnamiger Organ­ismen" ( I )1, with inleractions ranging (rom mUlualistic 10 parasitic (2). Hyphae of Ihe fu ngal symbiont may lie within a matrix of algal cells, adhere to these cells as apprcs­soria, invaginate these cells as haustoria, or occasionally penetrate cell walls and plus­mfl lcmmae (3). Long-tenn survival of the lichen association depends on b..1 lflnced growth of the symbionrs, yet this balance docs not preclude killing or saprobic digcs­rion of the algal symbiont (4). Lichen·fonn­ing fungi r~present many diverse lineages of

A. Gargas and P. T. DePrieSt. Department 01 Botany. NHB· I66, National MUS8lXIl of NallXlli H'iSlOI)'. Smlthso· !-.an instilUlIOl1. Wast*lgton, DC 20560. USA. M. Gnbe. nsblUl u Bota-lk. Karl·FflW&"'$·I.lo"MnoIAt Graz. tk*egasse 6, A.aQ1 0 Graz. Austria. A. T~. Botnska nst4utionen. Stodd'dms Uwef· $lief. S· I06 91. Stoc:khc*rl. Sv«ten.

Dicaryomycotina (5) that traditionally have been studied under Ihe rubric of Ii· chcnology. These lineages are not descend­ed from a single lichen-forming ancestor, yet it is not known how many limes, and in which groups. the lichen habit originated. By eXamining the phylOl,'Cneric position of lichen-forming fungi relative to saprobic or pathogenic fu ngi, we can address a funda­mental question of symbiont evolution: wherher mutualistic symbioses arc dcrived from more parasitic (onns (6).

To detennine the origins of the lichen habit, we includt.-d lichen-fonning fungi within a phylogenetic analysis of Amastigo-­mycota, members of EumycotH that lack motile Stages. The major lincflges of Amastigomycota-Basidiomycelcs, Asco· myceres, and Ihe paraphyleric zYb'Ol1lycetous fungi (7)-have few comparable morpho-­logical characters [Q serve as the basis (or ph~' logenl.' tic. hypotheses. For example, the

SCIENCE • VOL.268 • 9 JUNE 1995

group Oicaryomycotina is distinguished by the single morphological feature of dikary. otic hyphae (5). Even the sexual structures used to define these groups do not allow for comparisons. Additionally, many fung i lack sexual structures and cannot be unambigu. DUSly classified.

Unlike mOt"phological characters, molec· ular characters a llow direct comparisons among extant Eumycota. Specifically, se­quences of small subunit ribosomal DNA (SSU rONA) have been USt.oJ to propose phylogenetic hypotheses for fu ngi (8). TIle inclusion of SSU rONA sequences from fou r lichen-forming representatives has produced a highly resolved phylogeny for Ascomycetes and has demonstrated that lichen-forming fu ngi are a key to undersmnding ascomycete relations (9). Our study used SSU rONA sequences from 10 lichen. fonning fungi and 65 other fu ngi in a cladistic analysis, which produced twO equally parsimonious cla­dograms that diffen.'<i only in sister taxa re­lations within one clade of three fungi (10) (Fig. I). These phylogenetic h ypotheses sup­port Oicaryomycotina, Basidiomycetes, and Ascomycetes as monophyletic and resolve their relations (II). In the topologies, we identified the phylogenetic positions of li­chen-forming fungi and nOOes where discor· dance in lifestyles among sister taxa indicates an independent gain or loss of the lichen habit. In each case, it is most parsimonious to interpret the lichen habit as gained (I2).

Within Basidiomycetes, our phylogenetic hypothesis supports three independent origins of the lichen habi t, each corresponding to groups supported by morphological characters (13). The basal origin of the basidiolichen habit is within the coral fungi; a few species of Multidavula (Fig. 2A) form loose lichen ass0-

ciations with the green alga Coccomyxa or occasionally with cyanobacteria. An indepen­dent lichen association with Coccomyxa is represented by OmphalilUl umbeUifl!ra (Fig. 28), which produces typical gi lled mushrooms and is allied with the button mushroom Agar­icus bispurw and the oyster mushroom P/euro­!US ostTelUus. Another basidiolichen origin is indicated by Dicry<mel1Ul pavonia (Fig. 2C), whose unique haustoria penetrate the cya­nobacterium Scytonema. This tropical inhab­itant is most closely related to the wood­rotting SchizoplryUum commune. Two of th(! three basidiolichens, Mulliclawla mucida and O. urnbeilifl!ra, produce fnlit ing structures that are algae-free and closely resemble those of their non- lichen-forming relatives (/3). The loose associations these basidiolichens fonn with algal colonies require few changes in overnll morphology. These hasidiolichen ass0-

ciations may have arisen multiple t imes, per­haps quite recently, within each closely relat­ed group.

Within Ascomycetes the lichen habit arose at least twice, according to our phy-

lagenetic hypothesiS; other independent or­igins may be detected with the inclusion of other taxa ( 14) . The most basal origin is represented by Lecanora dispersa (Fig. 20), Porpidia cru.$w/ala. and Sphaerophorm globo­sus (Fig. 2E), members of Lecanornles (9) that commonly form intimate haustorial connections to coccoid green algae such as Trebouxia. The nearly 6000 species of Lecanorales include famil iar cruStose, fo li­ose, and fru ticase lichens wi th cup-shaped

- .-

fru iting structures. Other lichen-forming groups such as Caliciales, as represented here by the saprobe Mycocalicillln alboni­grnm, are sister taxa to Lecanor:.les. The calicialean lineage may have given rise to nonlichenized cleistothedal fungi, such as the laborntory model Aspergillus. A second origin of the ascolichen habit is in the lineage containing Arthonia radiaw (Fig. 2F) and allied spt.ociL'S of the order Arthoniales (/5), whose hyphae may even pcnetrnte

"

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. - ­. -­--L'::-==----I..:~'i. --=

~"'-t·r==--'-l • __ ----... ¥ .....-

~­--100 CIdno_ --• --

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•

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'-:;-:----­. --~",r-7----•• ••

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tJ<==~~~~'~'~; .~ . """""",-.-. ~_ Zygomycetous outgroups Fig. 1. PhylogenetiC relations within Amastigomyoota, as derived from parsimony ana~s Of 1927 nucIOOtides of SSU rONA sequences from 75 representative fungi. One of two equally parsimonious dadograms of 3491 steps is shown; the cladograms differ crit il sisler taxa relations wittWI the dade thaI indudesAgaricus bisportss, 0mphaIina umbeIIifera. and Aeurotus as/rea/us. Bootstrap percentages (2 I) from 200 replications are shown on each supported branch. The major fuolgaIgroups supported in this analysis are labeled adjacent to thai' nodes. lichen-forming ft.ngI are shown in green, rnyconflizaJ h.ngi ., pink. plant pathogenic fungi in blue, animal pathogenic h.ngi in orange, and saprobic fl..ngi in black; the green branches represent independent origins of the 1K;hen habit.

SCIENCE • VOL. 268 • 9 JUNE 1995 14"

Fig. 2. Representatives of the five independent ori· gins of lichen syrOOioses. (A) The coral flrIgus Mtifi­davu/a vamais (Schw.) A. H. Petwsen, a close reiativeofM. mucida, end&­cayilg 'MXld. (8 ) The 1Tl.ISh. room ~ tvdsoni· Ma (Jem.) Bigelow, a close relative of O. umbeltifera, on OI"gMc materials. (e ) The Jaiose 0icty0n6ma p8V(r

niB (Sw.) Parmasto en tr0p­ical soil. (D) The crustose LI3C8fI()(3 dispefsa (Pers.)

~. on rock. (E) The lrutiCose ~

g/cbo<u> -­en orgwic materials. IF) The cruslose Mhonia radiara (Pes.) Ach. on bark (A) ItTOugh (C) a-e Basidiomy­cetes, (0) ItTOugh (F) !WEI Ascanycetes, and (0) and (E) are members of the or­der Lecanorales. Photo­gaPls (22) a-e by C. Schei­degger~. V. With(B,C,0, and F). and K Rasbadl (1:).

their 1I1gai pllTlnef. typically the filamen­toilS green alga Trenwpohlia. This order of nearly 2000 5pccics is closely rdatl'<i to pcrithecial fungi, including the modd fun­gi NcuTmtxn'a crass(l and Podospora (lnsc­rilla. Scpamte origins o( the lichen habit in Lecanorn lt!S and ATlhoniales explain the nomble differences in their morphol­ogy. halislOrill, lmd a lga l symbionrs. In contrnst to the hasidio[ichcns, Hsco[ichcns ;tre intricaTe associations in wh ich the li­chen morphology differs from that pro­duced by ei ther of the symhionts cu[tUTL'<i ;txeniclllly. In Ascomycetes. lichen (ormll­lion is a dominant lifestyle. with nea rly half of the ~pecies associated with algae, and lichen origins arc relatively ancient and evol utionarily successful.

Myco[ogists would never propose thll! all fungi patho.'!l·nic to plants, or all fung i that (onn mycorrhi.lIe. aTe scp.·ua te cohesive units. However, fungi that form lichens have been stud ied and classified in bolation from odlcr fungi, even very recent[y (16).

1494

Here, we show thtlt lichen symbioses arose lit least five tinn.'S in phyl~encticlilly dis-­tant b'TOUP:;; the concept of lichen is thus ecologically ffieaninb.ful ( 17) hut not phy. logclletically meaningful. Within lhis phy_ [ogenetic context, the most ptlmsitic [i ­chen-forming fungi, Arthonia[es (18), arc closely related fO groups thm include vi ru­[ent plant pathogens (LLucoswma and Aber­naria), which suggcSb that lichen symhionts arose from pamsitic fungi. Lichen formation is not a primitive lifestyle; ot her lichen symhionts arose from prcJominlintiy mycor­rhizal fungi (basidiolichens) or from sapro­bic fungi (Lec:momles). Indeed, [ec:mo­mlean lichen symbionts may have given rise to fungi parasitic o n lichens (19). Fungi arc oppoTlunists: S'lprobcs ix.'Come symbionts; symhionts switch between mutualism and pamsitism. O n the basis of this phylogenetic analysis o( fungi in symbiotic lichen associ­ations, we find nosuppon for the tener that there is a general evolutionary prQI,'Tcssion from parasitism to mutualism.

SCIENCE • VOL 268 • 9 JUNE 1995

REFERENCES AND NOTES

1. "Different orgaAsms M1g together"jA. De Ba-y. o;e &xheh.ng w S)mbiose ~. France. 1879)1.

2. V. ~, me /..JdIen ~ ('BIaisdef. Walthll"Tl, MA, loon: D. L Hav.1<sworth, Crypto­gsm. Bot. 4. 117 (1994): __ In Essa~ in Plant TIb:OrIClmY, H. E. Street. 81. (Academic Press, New YOIt\. 1978). pp. 12:2-143: R. HaoDggar.Annu. Rev. PIsnI f'h)IsioI. Ptanl McJ. &01. 42, 553 (1991}.

3. A. ~ aod H. M. Jams. /..ichenes {Geag Tl1IEt­me. Stuttgart, Germany. 1973}.

4. v. AtmadjiIWlaod J. B. Jacobs.InAJgalS).mbosis. L J. Gotf. 81. (CambrIdgelJrjv. Press. 1983), pp. 141-112.

5. A. Tehier. 0aclslICs 4. 221 (19681. 6. See. lor ~. M. GaUIBry, PwasltISl1l and Sym­

biosis (SldgwidI and Jackson. LonOon, 1952); how­ever. seeD. J. Futuymaand R. M. May, In Genes., EooIogf. R. J. BIny, T. J. Cmw101'd, G. M. Hewitt. Eds. (BIackweI ScIentific, LonOon, 1991), pp. 139-, ...

1. T. O. Bnns et aI., McJ. ~. &01. 1, 231 (1992).

8. M.L BerbeeandJ. W. T~,MoI. BioI. Evol. 9. 278 (t992): M. 81ackwe1t. M}t::otIogi6 86. 1 (1994): S. I..antMk. O. ErIIsson. A. G!w"gas, P. GustaIssoo. Sysf. Ascc::Im)celLm 11. 101 (1993l; G. s. Soonz. J. W. T8yIor, A. Gargas, ~ 86, 212 (t994): J. W. Spatafora and M. BIad!weI./bid. 85, 912 (1993l:

E. C. SWMO and J. W. Ta'ytor. Ibid .• p. 923: P. O. WainrIghI. G. Hnde. M. l. SOgin. S. K. Stickel. Sci­ence 260. 340 (1993): H. Nist'Ida and J. Sug!yarna. Mol. 8ici. EvoI. 10. 431 (1993).

9. A. Garga$andJ. W. Ta'ytor.&p.~ 19. 7(1995). 10. fQr tti5 ~ SSU rO>IA SEQJeflC8S were 00.

tanId Iran rw. Iulgi. IrQd<lg leu AscorrtyceIas ~ IlIdiata (G6'lBirok arx:e5$IOI'I I'U'I'tl8' U23537). ~ ~ (U23538l. L.8amctis 00IeInJ (ln3539). Mel Sch:smatomma IJI(PdtVn (U2354O)1 Mel live Basacion'lyceIe ~ CIJS bisporus (U23724J. ~ PfNOnIIJ (lJ23541). ~ rru::dII (1.)23542). ~ IftIbeII/enJ (lJ23543). sod Pfa.roM; OS/I8fIfUS (1J23544~. DNA was ~led a'Id SSt) roNA was ~ by 1hIt pdymerase char'I teactoon (PCRI from lI6lgus.speciic ~ ~ as d&o scroeo In (91. DoI.tlIe-stranded PCR p-oduc1s were ~ as ci9saibed ~ or by the PA1ZM Reaat Rooctoon DyeOooxy lerrTW'1i11or c:yc:ie $flQ.JIS('Cing kit (AppIed Bio:sySIQm$) with detectiorl 0'l1l373A IIUItr matic seQl.I£IIldng appat'8tUS (Applied ~IOOlSJ. Sequence fragnElnts wete assanbIed 1l"r<IO..IaIy. These DNA sequences were ~ to 8 SSt) rONA sequences from 1I1e TOt !IU1hor's previous studies­LeCsnortI cfspeIsa 1l37535}. Lootia.t.tri::a (1..37536). Morr.heIIa slala (1..37537). Mj<localbl.rn ~ (1..37538). Peliza bada (1..37539). Pt:xp;da CflJSll'*'la (1..37540). SC8t>Iniil .sceurb'l.m (1...37541). and S{Xla8rophaus gbbosus (L37!532)-Md to 58 S& ~ avaiabIe !rom <JerBcnI: MemariII9I!emala (tXl5194). Alheia 0tvl1bechI (M55638). At.ri::u/Iria 8U'icuIII (l..22254).AI.ri:u/iriI pdyIrtdIa (l22255). ~ IBIus salarras (M94337). BuIEI'a Ml6 (XSOI79). Cab­CEra ccmea (1.22256). Csn:fdo I/Itlcwls (X(3497). ~ alaI"," (M83257). ~ ci1er8uS {M929911. 0'0nar1Un tbc:o::Ie (M94338I. O:.d::na CO'Ua (Z3024Q. ~ ~ (122257). ~ SlI1Btt.$ {l.222581. End:lgone ~ (X58724). Ettmascus aIlus (M83258). Etr rorun ntn.m (UX970). fi:lbasicfera /IlIOIbrna1S ~2n. Gtgaspc:wa abIda (ZI4OC1'3t. G)monj!ra lIS' a.etra (Z30238I. HetetoIexfusatlhus (l222591.I-is­/!:pBsrnII ~1#l1 (X58572. S4~. ~ aggegal8(Z30241).~8cfis(X51~. Llif;Mosp/l88tl1l bicoO" W202). ~ so:xti (X53499). LeuOoStOma ~ (M83259). ~ ~ (l.2E!OO6j. NeoIacI8 l'IIehI (727393!. NaJrospoof 0'8SSIJ (XD4971). Q;lhb$toma !.IItn (M83258). F'a'ldermtm hat1<n8ssi (M94339). F'I9ct!Ini!I nigrBIa (727400). PIeospora ~ (tXl5201). P/oo$pOra n.d$ (lXX)il75J. Pneo:.mocys/.is carini (XI2707), Podospcya ansErila (X54864). Pro-10f'Il)CeS nooya (011377). ~ gs/aI.f1o­SU7l (l22260!. ~ torIJIofdes (XS018O). S/IcdJ!IromjoQJS C&'eVisooo (J0 1353. 1.127607). Sdlizophyl.m c:omm\KI8(X54865). ~ myces pcxnb8 (XS4866). Septcro f'Qdorml (U04236). SpaIIUaris IraYida (Z30239). ~ Lni::oI:r (M597~. ~ jtTnsoni (l22261). ~ rosetIS (XS0181). Tsph­ma wiesnetI (012531. 0(1175). Thanalep/lorus OJ­ctIIl6tis (M9299Q). Thormo9scus crustaceus (M83263j. TIel", ca<ies (UX972). T/&'OOIl!I biace/t (l22262). TricIrJ$pOron aJ/1lrl8lII'I (X60182). Ustil!lg(:l ~(lO)973J.X&'oo::mJs~(M943401. Zoophthota cuIslaeiI (029949). and ~ m)Q!IS rouxi (X58057). TN 75 sequences were aq.ed wth 1h8 PfO!1lI'TI PIeUp!f>rOo'am MaruaI for the~Package.1/lnion8.Seplember 1994; CHoetics ~ Grouo. MadIsorI. 1M); gaps were reWoedbymarualf4JStm8nt.M~0I1927 n.d9otides from 75 tllX8 was used lor I)Ilf$imOny anaIysIs'M1h 1h81)'Og1'lm PAUP 3. 1 (.2IJ). No dIar.!c. tflfS were fIl<Ct.odDd. ioY8riiInI char!lclfIfS were ig­nored, III char!IcI(Q were eo.JaIy WIJiItIted. and bnn::h I8ngIhs ecr...aI to 0 were coIapsed to pcltfIo­mias. 1l'e a'IIIIysIs prcdIc:ed lft'OOIed netv.o:'ks that were rooted WIth 1tTee ~ous llngIas OOA­!JO.IP$. Two eo.JaIy ~ tre8S were pro­cLaJd. with tree I6"ogths of 3491. \XlI'ISi:sIeo::y lrdoes 01 0.3893. sod retentiol1 n:ices 01 0.694 1 : the tre8S diff~ oriy In sister taxa relations v.ithi1 ()'l8 dade 01 three fI.rgi (Fig. 1). Bootstrap peroentageS 121) to as· sess SIJPPOI1 for each brtn:t1 were determined lor 200 ~ 01 \he date sat. Bootstrap values 0/

>80% J)'O>'ided strong suppcrtlor \he I'l'IOI'lOPhyty 01 ~ su:::h as 1A:!IryomyooIna. AscomyceIes. and BasiOOrnyceIes.

II. TNs phyIogeneIX.: hypothesis suppcrts the mono· ph')+J 01 most got.pS ~ i'I tradition!II cIas· sifications. sod the additlon 01 taxa may resoMl f'ner reA!ltions. For exa"!llIe. In BasicbTryceles. Auicu-1ariaIes {represeflIed by Al.ri::I.Wi1I1lri:ui:1. A /XIIyo /1JCha. sod Pseudohydnum gelJtnostnIjis raoog­Itzsd as monopI'r)4eIlC. )'Ollis pI!Icement wiIrIIn lhe HornobasdorTry(es clade (defined by Muti::Ii!MJa rIl!.IIX1a. Thana~ a.a.meris. Spoo~ 1IIicUIor. and Alheia ~ IS probIernallC. In Asc:oo'rIVCetes, oriy the order PwIZales (nlpreseoted by Paliza bacia. G}ro-nitra ascuIIiWlla. Morche/IS 00108, /nEm1ISiII aggregala. and PlBctww flgel!l). here recxJgUed as~. Offers !rom \he first auttlor"s previous rnoIecI.kr p/1yIOgenI8S (9).

12. In Asccmtcetes. \he ~ 01 two"depeI;o;_"""",. QIWlS 01 \he Ik:hln ~ IS ITlOt9 ~ !han that 01 a si'Ige crigin wit! tIT98 ~ loss­es. In Basdoo1ycetas. \he hypothesis 0I1tTee inde­peodeoI gat1s 01 the Ii::hen S)offibiOSiS is more parsi. morlous. becaIJse II single origin WOJId reQtke one gain and aiglt losses . AItholql gain Mel loss can be variably weighted so that \he loss of \he Ii::hen symbi· osis is easier than ~s gain, this strategy ~ the necessary repIacemer1t of the lost IiChErI symbiosis with a gIIined SIIprObic. symbiotic. or parasitic hIIbit.

13. F. Qberwi1kler. Nova 1-Iec1wigr.!l 79. 739 (1984). 14. We predict CItlEw' ildepelldel.1 I}aInS ot the tIc:ha'l

symbiosis in Ascomycotes lineages not represented in INs analysis. especIatJ the ordiers DoIhIdeeIas. GrIIpt1dales. OstropalBS. and ~. -M'ictlln· CUde taxa that ere SllP'obes. par8Sites. and lichen symbionIs. FIner rBSOkJtion may detec1 IiChErI loss and PI within each oI lhese orclEn as wei as wrthon Arth:naIes and lecer1oraIe:s.

15. A. TEHer, Can. J. Bot. 68. 2458(t~. 16. L Marg.Jlisand K. V. Swartz. FWeKngdoms (free­

fl'\II"1. San Fnroasco. 1968l: ~. see O. E.

SCIENCE • VOL 268 • 9 JUNE !995

Eriksson and O. L Hawksworth. Syst. Asconyce­lum 12. 52 (1993).

17. L Kapper'l. Ct)ptogam. Bo/. 4. 193{1994). 18. S. C. Tucker, S. W. Matthews, R. L Chaprra1. In

TroPcaI Uchens: Their Systamalics, Corl:s&val.i::ln and Ecotlgy. O. J . Galloway. Ed. (CIarEnlon Pres:s. 0KI0rd. 1991). pp. 111-191.

19. D. L Hawksworth, J. HallOO Bot. LBb. 52. 323 (1962); J. PoeIt. Pbnta (Haic:iIII:log) 51 . 288 (19581: G. R!wnboId aod D. Treibel. 8tJI. 1.X:henc:J. 48. 1 (1992).

20. D. L SwofIord. PAUP; Pt'IyibgEnelc Analysis lJ$;lg ~. V«SIO'I3. I ~ Naur.!I: History Str· '1&1. Q1arnpaIgn, tL 1991).

21. J. FelsMsterl. Evot1Iion 39. 783 (1965). 22. TlYee photogaptls (FIg. 2. B. E. sod f) ere repr0-

duced!rom V. Wnh. Die Flechten Baden-W!)ftlm­

/:J8'9S (Eugen l.I1r!1ef. Stuttgart. Getmany. ed. 2. 1995). pp. 137 (Fl. 619 (8). and 863 (E). Uged by -. 23. We thankV. 'tMh. C. Sc::heocIegge.-. aod K. Rasbactl lor color photographs: the laboratory of MoII'IcUar Systematics of the Smrthsoniarl Inst~utoo lor DNA sequenaog facl!ities: D. L. Swofford and P. O. Lewis tor Sl.WOft of p\Ty1ogeoeIic!l!llllyses:!I!ld D. J. Fu· luyrna. D. L Hawksworth. F. 0be.'winkIer. R. H. Pe· tersen. A. Y. Rossman. M. L SogIn. A. R. Horn­buckle. !I!ld llYee III'oOI'lY'f1OU reWlweis lor rI13r'IJ-­scriPt cornrnents. A.G. and P.T.D. IhinlM.A. Faust. V. A Ftx*, M. O. Kane, W. J. Kress. H. E. Robw'1sorI. Mel especiaIy J. W. Taytor lor support and enccu­agament. Supported by a Srnthsoria'l Insl~ution posldoc1ori11 feIowship (A.G.). i!. Srrittlsalierl tnst~u­lion Scto:oIarti Stucies gam !Ind a Natioo!II Mo.-..m 01 Naltn History Research 1rOtii!.tives award (p.T.D. *'" A.G.). i!. Srnithsoniarl nstitutioo VisItng ScIentISt IeIowshIp *'" Foods ltI' ~ del' wissen­schattichlln Forsdu1g (M.G.). aod 1h8 Swedish Na· tlOl"l1ll Reseerch Cotn:::I (A. T .).

21 December 1994: accepted 14 March 1995

1495