M.N. Dawson Macro-morphological variation among cryptic ...

1 Macro-morphological variation among cryptic speciesof the moon jellyfish, aurelia (Cnidaria: Scyphozoa)Received: 1 October 2002 / Accepted: 24 February 2003 / Published online: 6 May 2003 Springer-Verlag 2003 AbstractMorphological variation in qualitative andquantitative features is compared among species ofAureliadefined a priori using molecular criteria. Macro-morphological features were more numerous than pre-viously implied (28 cf. 17), most were variable (26 of 28),and all species were morphologically distinguishableusing univariate, multivariate and phylogenetic statis-tics. However, due to discrepant morphologicaldescriptions,Aureliaspp. 3, 4, and 6 could not beassigned reliably to any previously described species,and there are still insufficient macro -morphologicalcharacters and variation to reconstruct a statisticallyrobust phylogeny for even the 12 known species ofAurelia.

2 Yet it is shown thatAurelia auritais most likelyendemic to the boreal Atlantic Ocean and northernEuropean seas, aurelia labiatais neither as morpho-logically diverse nor widespread as recently described,and the circumglobalAureliasp. 1 is probably intro-duced across much of its Supplementary Materialis available for thisarticle if you access the article at A link in the frame on theleft on that page takes you directly to the taxonomic publications on species of themoon jellyfish,AureliaPe ron & Lesueur, have providedlittle consensus. In 1910, Mayer noted that adozen species ofAureliahad been described although herecognized only 13 varieties in 3 reasonably well-definedtypes ,A. auritaLinnaeus,A. labiataChamisso andEysenhardt, andA. solidaBrowne, on the basis that themorphological distinctions between many of the spe-cies are not well ascertained, and there are numerousvarieties of local races (Mayer 1910).

3 By the 1960s,however, about 20 species ofAureliahad been de-scribed (Kramp 1968) although Kramp (1961) recog-nized just seven,A. aurita,A. coeruleavon Lendenfeld,A. colpotaBrandt,A. labiata,A. limbata(Brandt),A. solida, andAureliaspp. [no authority], suggesting that it is better to retain too many species than to unitespecies whose identity cannot be stated with certainty,thereby causing confusion in zoogeographical discus-sions . Yet, within a few years, Kramp (1965) discussedjust five types and subsequently recognized only twospecies, a circumglobal, almost cosmopolitan,A. auritaand an arcticA. limbata(Kramp 1968). His reasonswere that certain structural features .. emphasized ascharacteristic of certain forms .. may frequently be ob-served in complicated combinations, even within one andthe same individual and that others may be changedduring preservation , are variable within one and thesame population , or dependent on the age and devel-opmental stage of the individual (Kramp 1968).

4 The occurrence of just two species ofAureliawasaccepted until the late 1990s (Russell 1970; Larson1986, 1990; Arai 1997) despite the publication of allo-zyme data indicating at least three distinct forms ofA. aurita(Zubkoff and Lin 1975). Additional proteinelectrophoretic data, coupled with morphologicalanalyses, in the mid-1990s strengthened the evidencefor cryptic species ofA. auritawithin the Pacific Ocean(Greenberg et al. 1996) and, soon after, one ofMarine Biology (2003) 143: 369 379 DOI DawsonCommunicated by Humphrey, SydneyM. DawsonCentre for Marine and Coastal Studies,University of New South Wales,Sydney, NSW 2052, AustraliaE-mail: +61-2-9385-3450M. DawsonDepartment of Organismic Biology,Ecology and Evolution, University of California,621 Charles E. Young Drive South,Los Angeles, CA 90095-1606, USAM.

5 DawsonCoral Reef Research Foundation, Koror, PalauKramp s (1961) seven species, the northeastern PacificA. labiata, was again recognized (Wrobel and Mills1998). DNA sequence data describing at least thirteenspecies ofAurelia, includingA. aurita,A. labiata, andA. limbatafollowed ( Dawson and Jacobs 2001; Schrothet al. 2002; Fig. 1), as did formal redescription ofA. labiata(Gershwin 2001). However, morphologicaland molecular data remained divided on several points,including the identity and range ofA. aurita(Dawsonand Jacobs 2001; cf. Schroth et al. 2002), the mono-phyly ofA. limbata(Schroth et al. 2002), and theextent and diversity ofA. labiata( Dawson and Jacobs2001; cf. Gershwin 2001).The disagreement between morphological andmolecular descriptions ofAureliamay have severalsources. One is a dearth of morphological characters anda second is high variability in those that exist (Kramp1968; Greenberg et al.)

6 1996). A third has been appar-ently idiosyncratic decisions regarding what constitutemorphological characters that are independent (Green-berg et al. 1996), reliable (Kramp 1961), or sufficient todelineate species (Gershwin 2001; Table 1). Similar is-sues have affected molecular studies. For example, allisozymes do not provide the same information, thetaxonomic implications of different levels of isozymevariation are unclear, and some isozyme patterns are too complex and variable for establishing relation-ships amongAurelia(Zubkoff and Lin 1975). WhileDNA sequences were sufficient to establish species-leveldifferences amongAurelia, they also were too variable toreconstruct a robust phylogeny ( Dawson and Jacobs2001; Schroth et al. 2002). In spite of these problems andin contrast to morphological data, however, wheremolecular analyses have overlapped geographically, theyhave recognized the same divisions within a morpho-logicalA.

7 Auritaspecies complex ( Dawson and Martin2001; Fig. 1).The failure of morphological studies to reach aconsensus may also be partly attributable to their po-tential for circularity. In the absence of independentassessment criteria, the iterative process of identifying good morphological characters and good morpho-logical species may be attracted to a stable but incor-rect solution (Sneath 1995; for additional briefcomments on this issue see Swofford et al. 1996 andGhiselin 1997). Molecular data therefore provide animportant opportunity to evaluate independently theutility of morphological data in systematic studies(Knowlton 2000; Roca et al. 2001).Here, morphological variation among four molecu-larly identified cryptic species ofAurelia(Fig. 1; Ta-ble 2) is quantified and used to resolve several outstandingtaxonomic issues in the genus.

8 The intention is not todescribe formally any species delimited by molecular data,nor is it to provide a definitive list of characters for use inspecies descriptions; these tasks should await collection ofadditional data and a more comprehensive revision of thegenus. Rather, the intention is to promote the quantitativeand objective investigation of morphological variation inAureliaand other medusae that, despite advances instatistical and phylogenetic methods in recent decades(Sneath 1995; Felsenstein 2001), generally has been lack-ing ( Gershwin 2001).Materials and methodsMolecular phylogenetic analysesThe number of molecular lineages ofAureliadescribed is unclearbecause sequence data published separately by Dawson and Jacobs(2001) and Schroth et al. (2002) have not been compared. InternalTranscribed Spacer One (ITS1) sequences characterizing lineagesfound by Schroth et al.

9 (2002) were downloaded from GenBank(AF461405 AF461412) and aligned with sequences from DawsonFig. 1 Single shortest unrootedgene tree (length 702 steps;consistency index )resulting from maximumparsimony analyses ofpublished Internal TranscribedSpacer One originally publishedin Schroth et al. (2002) areindicated by their originalthree- or four-letter identifier;all other sequences wereoriginally published in Dawsonand Jacobs (2001). Bootstrapvalues >50% are shown aboveeach branch. The morphologiesof taxa in bold font (sp. 1, sp. 3,sp. 4, ) are described in thisstudy370and Jacobs (2001) in ClustalX (Jeanmougin et al. 1998) using gapopening:extension weighting of 10:1 and transition:transversionweighting of The alignments were checked by eye and obviouserrors corrected in Se-Al (Rambaut 1995). Aligned data,including and excluding gapped positions, were analysed inPAUP* b10 (Swofford 2002) using maximum parsimony crite-rion to select the best trees found during a branch-and-boundsearch of possible trees.

10 Bootstrap analyses (2,000 replicates) inPAUP* b10 employed the heuristic search option using tree-bisection-reconnection (10 replicates) saving 5,000 trees 707steps (except in replicates where all trees were >707 steps) andsearching on all saved collectionBetween November 1996 and September 1998, four molecularlydefined species ofAurelia( Dawson and Jacobs 2001; Fig. 1;Table 2) were studied in eight [SpinnakerCove (SCLA) and Marina del Rey (MRLA), Los Angeles], [Risong Cove (RCA) and Tab Kukau Cove (TKCU), Palau], [Big Jellyfish Lake (BJLK), Ongael Lake (OLO), andOngeim l Tketau (OTM), Palau], [Ngell Channel(NCK), Palau]. At each location, medusae with four gastric poucheswere dipped from the water by hand and carefully transferred to aflat measuring tray. Medusae falling within two size categories,150 5 mm and 250 10 mm bell diameter (between distal tips ofopposed interradial rhopalia), were quickly transferred to bucketsof native water ( 29 34&depending upon location) and trans-ported immediately to the Coral Reef Research Foundation(CRRF; Palau) or the University of California, Los Angeles, wherethey were placed in temporary aquaria containing ambient salinitywater ( 29 34&).