18 S rRNA gene sequences are presented for Ahnfeltia plicata, Chondrus crispus, Furcellaria lumbricalis and. Palmaria palmata, commercially important marine ...
Journalof Applied Phycology 4: 379-384, 1992. © 1992 Kluwer Academic Publishers. Printed in Belgium.
379
The 18S rRNA gene sequences of four commercially important seaweeds* C.J. Bird,' C.A. Murphy,' E.L. Rice 2 & M.A. Ragan' LInstitutefor Marine Biosciences, National Research Council of Canada, 1411 Oxford St. Halifax, N.S., Canada B3H 3ZI; 2 Biological Sciences Branch, Scotia-FundyRegion, Department of Fisheriesand Oceans, P.O. Box 550, Halifax, N.S., Canada B3J 2S7 Received 30 July 1992; revised 10 August 1992; accepted 25 August 1992
Key words: Ahnfeltia, Chondrus, Furcellaria,Palmaria,rRNA sequence
Abstract 18 S rRNA gene sequences are presented for Ahnfeltia plicata, Chondrus crispus, Furcellarialumbricalis and Palmariapalmata, commercially important marine algae of the North Atlantic. The sequences range from 1765 to 1777 nucleotides in length, with guanine+ cytosine content of 50.1% to 52.4%. Sequence divergence between species in different orders was 11.3-12.3 %, whereas the variation between C. crispus and F. lumbricalis, both from the Gigartinales, was only 3.6%. Based on limited experience with other groups of Rhodophyta, these sequences obtained from single populations are likely to be representative of the species as a whole, with little variation expected among conspecifics regardless of morphological aberration or apparent genetic isolation.
Introduction The increasing application of modern biochemical techniques in algal taxonomy has brought species concepts under more critical scrutiny. In particular, there has been an upsurge in the use of nucleic acid characters to differentiate and characterize algal taxa (for reviews see Olsen, 1990; Coleman & Goff, 1991). As genetic variations are discovered and evaluated, it is becoming apparent that thorough characterization of species and strains is imperative if the seaweed industry is to realize the potential of certain taxa. The gene currently used most extensively in phylogenetic studies is that encoding the riboso* NRCC 34824.
Government of Canada..
mal RNA molecule present in the small subunit of the ribosome. In mitochondria and chloroplasts, as in prokaryotes, this molecule typically consists of about 1500 nucleotides and, based on older sedimentation-velocity centrifugation results, is termed 16S rRNA. The nuclear-encoded homologue of eukaryotes typically comprises about 1800 nucleotides, and sediments at 18S. 18S rRNA gene (rDNA) sequences have been used widely to infer relationships among higher taxa of organisms, from families upwards; little has been reported on its variability within species or among congeners of algae (Medlin et al., 1991; Bird et al., 1992). As part of a survey of 18S rDNA sequences among red algae, towards establishing a gene phylogeny for the Rhodophyta (Bird, Murphy
380 et al., 1991), we have determined this sequence for four commercial species occurring in eastern Canada: two carrageenophytes of the order Gigartinales, Chondrus crispus Stackhouse (Gigartinaceae) and Furcellaria lumbricalis (Hudson) Lamouroux (Furcellariaceae); the agarophyte Ahnfeltia plicata (Hudson) Fries from the Ahnfeltiales (Ahnfeltiaceae); and an edible alga, Palmaria palmata (Linnaeus) Kuntze, from the Palmariales (Palmariaceae). All are common species of cold-temperate to subpolar waters of the North Atlantic and adjacent Arctic Oceans (Bird & McLachlan, 1992), and are restricted to this region except for A. plicata which is circumpolar in both hemispheres (Maggs etal., 1989). Although there is little dispute as to the identity of these species, the degree of phenotypic variation in some of them is sufficient to warrant further taxonomic investigation (e.g., Chen & Taylor, 1980; Gutierrez & Fernandez, 1992). Thus, toward further characterization of these species, we present the 18S rDNA sequences from representatives collected in the Maritime Provinces of Canada (Table 1).
Materials and methods Collections of algal material, and the corresponding voucher specimens in the herbarium of the National Research Council (NRCC), were as follows: Ahnfeltiaplicata - Sandy Cove, Halifax Co., Nova Scotia (44 ° 28' N, 63 ° 34' W), 13 Apr. 1989, NRCC 10773; Chondrus crispus - Sandy Cove, Halifax Co., Nova Scotia (44°28' N, 63 34' W), 25 Jan. 1990, NRCC 10803; Furcellarialumbricalis - Orby Head, Queens Co., Prince Table 1. Summary of nucleotide (nt) composition of the 18S rDNA sequences. Species
Total nt*
A
G
C
T
G+C%
Ahnfeltia plicata Chondrus crispus Furcellarialumbricalis Pabnariapalmata
1765 1777 1774 1771
418 437 428 428
531 521 533 518
393 369 375 385
423 450 438 440
52.4 50.1 51.2 50.9
* Including amplification primers.
Edward Island (46 ° 30' N, 63 ° 20' W), 3 June 1990, NRCC 10812; Palmariapalmata - Sandy Cove, Halifax Co., Nova Scotia (44028' N, 63 34' W), 22 Mar. 1989, voucher specimen not
prepared owing to insufficient sample. Fresh thalli for extraction were cleaned of epiphytes and other foreign matter, and stored in 5 g lots at -80 °C pending further processing. DNA was extracted according to the method of Rice and Bird (1990), and amplification, cloning and sequencing of the 18S rRNA genes were performed as described by Bird et al. (1992).
Results and discussion The nucleotide sequences for the 18S rRNA genes in the four species are presented in Fig. 1. All nucleotides were unambiguously assigned and, including the amplification primer regions, the sequences range from 1765-1777 nucleotides (Table 1). This length comprises an extra cytosine at the 5' end, included by convention as a component of the primer, and spans the entire gene except for two relatively unconserved nucleotides at the 3' terminus. No introns were observed. The sequences are deposited in the EMBL data base, with accession numbers Z 14139 (Ahnfeltia plicata). Z14140 (Chondrus crispus), Z14141 (Furcellaria lumbricalis) and Z 14142 (Palmariapalmata). This represents the first publication of 18S rDNA sequences for these species, except P. palmatafor which a sequence was published with erroneous attribution to Porphyra umbilicalis (Hendriks et al., 1991). This sequence is nearly identical with the present one for P. palmata, yet markedly divergent from our sequences for Porphyra umbilicalis and several of its congeners (Ragan et al., unpubl.). The only other DNA sequence published for any of these genera is a 5S rRNA gene sequence ascribed to P. palmata from Japan (Lim et al., 1986). Pairwise comparison of the sequences (Table 2) revealed similarities of 87.4-88.7o%, or divergences of 11.3-12.6%, between orders. The similarity of 96.4% between the sequences for C. crispus and F. lumbricalis reflects their common
381 A.
plicata
caacctggttgatcctgccagtGGTATATGC
C.
crispus
caacctggttgatcctgccagtG
F.
lumbricalis
caacctggttgatcctgccagtGGTATATGCT
P. palmata
caacctggttgat
TCGTCTCAAGGACTAAGCCATGCAAGTGTAAGTATAAGTGAAT
GTATATGCTTGTCTCA
AGGACTAAGCCATGCAAGTGTAAGTATGAGTGAAT
TAAGCCATGCAAGTGTAAGTATGAGTGAAT TGTCTCAAAAGGAC
cctgccagt GGTATA TGCTTGTCTCAAGGACTAAGCC
TATAAGTAATT
TGTACAAcGAAACTGCGAATGGCTCGGTAAAACAGCTATAGTTTCTTCGATGATACCTACTACTCGGATAACCGTAGTAATTCTAGAGCT TGTACAACGAAACTGCGAATGGCTCGGTAAAACAGCTATAGTTTCTTCGATGGTAACTACTACTTGGATACCCGTAGTAATTCTAGAGCT TGTACAACGAAACTGCGAATGGTTGGTAAAACAGCTATAGTTTCTTCGATGGTAACGACTACTTGGATACCCGTAGTAATTCTAGAGCT TTTACGACGAAACTGCGAATGGCTCGGTAAAACAGCTATAGTTTCTTCGATGGTACCTACTACTCGGATAACCGTAGTAATTCTAGAGCT AATACGTGCCGCAACGCGGGG--TAACCCGTGGTACAAGTTAGATAA-CAGGCCGACGCTTGACGATTCATAACTTTTTTTCTGATCGCG AATACAAGCCTTAaAGCGACATTTATGTCGTGGTATAAATTGGAGATACAAACCAATGTTTGGTGATTCACAATTTCTTTTCTGATCGCA AATACATGCCATAAAGCGACGCTTGCGTCGTGGTATAAATTGGAGATACAAACCAACGTTTGGTGATTCACGATTTCTTTTCTGATTGCA AATACGTGCCACAACGCGGGG--TAACCCGTGGTACCAATCAGATAT-CAAACCAATGTGTGGTATTCATGATTTTTTTTCTGATCGCA CCTTGTGCGCGACGCATCGTTCAAATTTCTGACCTATCAACTTTG-ACGTGAAGGTATTGTCTTCACGTGGTTGTGACGGGTAACGGACC CGTTA-GTGCGACGCATCGTTCAAATTTCTGACCTATCAACTTTGGATGGTAAGGTATTGTCTTACATGGTTGTGACGAGTGACGGATC CGTTT-GTGCGACGCATCGTTCAAATTTCTGACCTATCAACTTTGGATGGTAAGGTATTGTCTTACATGGTTGTGACGGGTAACGGACC CGTTA-GTGCGACGCATCGTTCAAATTTCTGACCTATCAACTTTCGATGGTAAGGTATTGTCTTACCATGGTTGTGACGGGTAGCGGACC GTGGGTGCGGGACTCCGGA
AG
GAGGAGCCCAATAAGAGACGGCTACCCAATCCTGACACA
GTGGGTGCGAGACTCCGGAAGGGAGCCTGAGAGACGGCTACCACATCCAAGGAAG
CAGGCGCGCAAATTACCCAATCCGGATACC
GTGGGTGCGGGACTCCGGAGAGGGAGCCTGAGAGACGGCTACCACATCCAAGGAAGGCAGCAGGCGCGCAAATTACCCAATCCGGACACC GTGGGTGCGGGATTCCGGAGAGGGAGGCGCGCAAATTACCCAATCCTGACAAAACCCAACCGACACA GGGAGGTAGTGACAAGAAATAGCAATAGAGGGCCC-AATGGGTTTTCTAATTGGAATGAGAACAAGGTAAATAGCTTATCGAGGATCCAG GGGAGGTAGTGACAAGAAATAGCAATAGAGGGCCC-AACGGGTTTTCTAATTGGAATGAGAACAAGGTAAACAGCTTATCGAGGAGCCAG GGGAGGTAGTGACAAGAAATAGCAATAGAGGGCCC -AACGGGTTTTCTAATTGGAATGAGAACAAGGTAAACAGCTTATCGAGAGCCAG GGGAGGTAGTGACAAGAAATATCAA
TAGAGGGCGTTTATACGTCTTCTAATTGGAATGAGAACAAGGTAAACAGCTTATCGAGGATCCAG
CAGAGGGCAAGTCTGGTGCCAGCAGCCGCGGTAATTCCAGCTCTGCTTGCGTATGTCACCGATGATGCGGTTAAAACGCTCGTAGTCGGA CAG
AGTCTGGTGCCAG
GTC GCAA TGGTAATTCCAGCTCTGTAAGCGTATACCAAAGTTGTTGCAGTTAAAACGCTCGTAGTCGGA
CAGAGGGCAAGTCTGGTGCCAGCAGCCGCGGTAATTCCACTCTGTAAGCGTATACCAAAGTTGTTGCAGTTAAAACGCTCGTAGTCGGA CAG
AG
GG
CAAGCTGGTTT
GCTCTGTAAGCGTATACCAAAGTTGTTGCAGTTAAAACGCTCGTAGTCGGA
GGTTGGCGGGGGCGTCTGGCGGAGAGTAAATCTTTGTCGGTC-GCGCCTGCTTTTGTGGAGGGCGCGAGCGGGCGGCTTTACTGTCGCGC GGTTGGCGGCGGAGTCCAGGGCGTCCTCGCGGACGGATCTGGAGTTGGCCGCCTTTGTGGATGGGGGCCTAGTGGAGCTTCACTGCTTAT GGTTGGCGGGCGACCTGGGGCGTCTTCACGGACGGATC-CAGGGCGGCCGCCTTTGTGGAGGGGGGCCCAGTGGAGCTTCACTGATTCAC TTTTGGCCGTGGCCCGTGGCGCTGTGCGCGTAATGCGTGCGGCGCTGGGGCGCGCTTTTGTGGAGGGCGGCGCGTTGTGGCTTCCGCCTTTTGTGGCGTGGG GTTCG-CGGCGCCACCGTTTACTGTGAATAAATTAGAGTGTTCAAGCAGGCGTTTGCCGTGAATACATTAGCATGGAATAATAGAATAG TGTGGTCGCTGCCACCGTTTACTGTGAAAAAATTAGAGTGTTCAAAGCAGGCGTTTGCCATGAATACATTAGCATGGAATAATAGAATAG TGTGGTCGCTGCCACCGTTTACTGTGAAAAAATTAGAGTGTTCAAAGCGGGCGTTTGCCATGAATACATTAGCATGGAATAATAGATAG CGT-GTCGGCGCCACCGTTTACTGTGAAAAAATTAGAGTGTTCAAAGCAGGCGTTTGCCGTGAATACATTAGCATGGAATAATAGAATAG GACCTTGT-CCT-TTTTGTT
GGTTTGTGAGGCCGAGGTAATGATTAAGAGGGACGGTTGGGGCATTTGTATTCCGGCGTCAGAGGTGAA
GACCTGTTTCCTGTTTTGTTGGTTTGTGAGGATCGGGTAATGATTAAGAGGGACGGTTGGGGGCATTTGTATTCCGGCGTCAGAGGTGAA GACCTGTTTCCTGTTTTGTTGGTTTGTGAGGAACGGGTAATGATTAAGAGGGACGGTTGGGGGCATTTGTATTCCGGCGTCAGAGGTGAA GACTTGGTTTCTATTTTGTTGGTTTGTGAGAGCCGAGTAATGATTAAGAGGGCCGGTTGGGGGCATTTGTATTCCAGCGTCAGAGGTGAA Fig. 1. Nucleotide sequences of the 18S small-subunit rRNA genes from the four species of algae, aligned by eye. Lower-case letters at the 5' and 3' ends of the sequences designate the amplification primers. The initial cytosine at the 5' end is actually external to the gene but is included by convention, as a component of the primer.
382 ATTCTTGGATTGCCGGAAGACAGACCGCTGCGAAAGCGTCTGCCAAGGACGTTTTCATTGATAGAACGAAAGTAAGGGGATCGAAGAC ATTCTTGGATTGGCGGAAGACAAACGGCTGCGAAAGCGTCTGCCAAGGACGTTTTCATTGATCAGACGAAAGTAAGGGGATCGAAGAC ATTCTTGATTGGGGAAGACAACAGCTGCGAAAGCGTCTGCCAAGACGTTTCATTGATCAAGAACGAAATAAGGGATCGAAGAC ATTCTTTGCTGGAACAAACCGCTGCGAAAGCGTCTGCCAAGGACGATTTCATTGATCAAGAACGAAAGTAAGGGGATCGAAGAC
GATCAGATACCGTCGTAGTCTTTACTATAAACGATGAAACTGGGGATCGGGCGGGACTGAATTT-GGCCCGCCCGGGACCCTCCGGGAA GATCAGATACCGTCGTAGTCTTTACTATAAACGATGAGGACTGGGGATCGGGGAGGACTGTATTTTGGCCTACCCGGCACCCTTCGGGAA GATCAAGATACCGTCGTAGTCTTTACTACGATGAGGACATCGGGCAGGACTGTATTTTGGCCTGCCCGGCACCCTTCGGGAA GATCAATACCGTCGTAGTCTTTACTATAAACATGAGAACTGGGGATCGGGCAGGCATTACGAT-GACCTGTCCGGAACCCTCCGGGAA
ACCAAAGTGTTTGCTTTCCGGGGGGAGTATGGTCGCAAGGCTGAAACTTAAAGGAATTGACGGAAGGGCATCACCGGGTGTGGAGCCTGC ACCAAAGTGTTTGCTTTCTGGGGGGAGTATGGTCGCAAGGCTGAAACTTAAAGGAATTGACGGAAGGGCATCACCGGGTGTGGAGCCTGC ACCAAAGTGT
TTGCTTATTCTGCAAGGCTGAAACTTAAAGGAATTGACGGAAGGCATCACCGGGTGTGGAGCCTGC
ACCAAAGTGTTTGCTTTCTGGGGGGGAGTATGGTCGCAAGGCTGAAACTTAAAGGAATTGACGGAAGGCATCACCGGGTGTGGAGCCTGC GGCTTAATTTGACTCAACACGGGGAAACTTACCAGGTCCGGACATAGTGAATTGACAGATTGAGAGCTCTTTCTTGATTCTATGGTTG GGCTTAATTACTCAAC
AAACTTACCAGGTCCGGACATA
A
TTGACAGATCTGAAGTCTTTCTTGATTCTATGGTTG
GGCTTAATTTCACTCAACACGGGGAAACTTACCAGGTCCGGACATAGTGAGGATTGACAGATTGAAGCTCTTTCTTGATTCTATGGTTG GGCTTAATTTTGACTAAACGGGAAACTTACCAGGTCCGGACTAGTGAGGATTGACAGATTGAGAGCTCTTTCTTGATTCTATGGTTG
GTGGTGCATGGCCGTTCTTAGTTGGTGGAGTGATTTGTCTGGTTAATTCCGTTAACGAGCGAGACCTGGGCGTGCTAGCTAGGGCGGGCT GTGGTGCATGGCCGTTCTTAGTTGGTGGAGTGATCTGTCTGGTTAATTCCGTTAACGAGCGAGACCTGGGCGTGCTAGCTAGGCGCCAGT GTGGTGCATGGCCGTTCTTAGTTGGTGGAGTGATCTGTCTGGTTAATTCCGTTAACGAGCGAGACCTGGGCGTGCTAGCTAGGCGCGACT GTGGTGCATGGCCGTTCTTAGTTGGTGGAGTGATTTGTCTGGTTAATTCCGTTAACGAGCGAGACCTGGGCGTGCTAACTAGGGGCCGCT
ATCGCTT---GATAGTA- - -CTGACCTTCCTAGACGGACTGTGGGCGTCTAGTCCACGGAAGCTCCAGGCAATAACAGGTCTGAGATGCC ACCGTTTTTGGTACTGAGGCTTGCCTTCCTAGACGGACTGTGGGCGTCTAGTCCACGGAAGCTCCAGGCAATAACAGGTCTGAGATGCC ACC-CTTGT-GGTAG
TGAAGG
ACTGCGGGCGTCTAGTCCGCGGAAGCTCCAGGCAATAACAGGTCTGAGATGCC
AC--CATTGTGTAGCTG-TTCGCCCCTTAGACGGACTGCGGGCGTCTAGTCCGCGGAAGCTCCAGGCAATAACAGGTCTGAGATGCC
CTTAGATGTTCTGGGCCGCACGCGTGCTACACTGAGCGGGTCAACGGGTGAGGATGTGCGAGAGCGCTTCCCAACCCCCAAACCCGCTCG CTTAGATGTTCTGGGCCGCACGCGTGCTACACTGAGCGGGTCAACGGGTGAGGATGTGCGAGAGCGCTTCCTAATCTCTAAATCCGCTCG CTTAGATGTTCTGGGCCGCACG
CGTGCTACACTGAGGAGCGAGAGCGCTTCCCAATCTCTAAATCCGCTCG
CTTAGATGTTCTGGGCCGCACGCGCGCTACACTGAGCGGACCAACGGGTGAGGATGCGCGAAAGCGTTTCCCAATCCCCAAATCCGCTCG
TGCTGGGGATCGAGGCTTGCAATTATCCCTCTTGAACGAGGAATACCTTGTAGGCGTGGGTCATCATCCCGCGCCGAATACGTCCCTGCC TGCTGGGGATCGAGGCTTGCAACTTTCCCTCTTGAACGAGGAACACCTTGTAAGCGTGGGCTCATTCCGCGCTGAATACGTCCCTGCC TGCTGGGGATCGAGGCTTGCAATTTTCCCTCTTGAACGAGGATACCTTGTAAGTGGGTCATCATCCCGTGCTGAATACGTCCCTGCC TGCTGGGGATAGAGGCTTGCAATTTTCCCTCTTGAACGAGGAATACCTTGTAAGCGTGGGTCATCAGCCCGCGCTGAATACGTCCCTGCC CTTTGTACACACCGCCCGTCGCTCCTACCGATTGAGTGGTCCGGTGAGGACTCGGGACCGC-GCCGACTAGCGCGTCTAACGCGTTGGTT CTTTGTACACACCGCCCGTCGCTCCTACCGATTGAGTGGTCCGGTGAGGCCTTGGGAGGGATGGATGGATTGTG-
-TTT-CACAAACTAT
CTTTGTACACACCGCCCGTCGCTCCTACCATTGAGTGGTCCGGTGAGGCCTTGGGGGGGATGAATGGACCGTG-
-TTT-CACGGACCGT
CTTTGTACACACCGCCCGTCGCTCCTACCATTGAGTGATCCGGTGAGGCTTTGGGAcTGCCGCGGTTGAGGCG--TTTACGCCCTGGCC
GTTGTGGAAACTTGTCCAAACCTTATCACTTAGAGGAAGGAGAAGTCGTAACAAGGTTTCCgtaggtgaacctgcagaaggatcaagc CTGGCCCAAACTTGGTCAAACCTTATCACTTAGAGGAAGGAGAAGTCGTAACAAGGTTTCCgtaggtgaacctgcagaaggacagaat TTGGCCCGAACTTGGTCAAACCTTATCACTTAGAGGAAGGAGAAGTCGTAACAAGGTTTCCgtaggtgaacctgcagaaggtcagaat GCAGTGGGAACTTATCCGAACCTTATCACTTAGA
GGAAGGAGAAGTCGTAA
Fig. .I (continued).
CAAGGTTTCCg tagcgtaacctgcagaaqqacagaat
383 Table 2. Sequence divergences (above asterisks) and identities (below asterisks), in %, based on pairwise alignments. Six variable nucleotide positions in the 3' amplification primer have been excluded.
Ahnfeltia plicata Chondrus crispus Furcellarialumbricalis Palmariapalmata
A. plicata
C. crispus
F. lumbricalis
P. palmata
* 87.4 87.8 88.7
12.6 * 96.4 88.2
12.2 3.6 * 88.7
11.3 11.8 11.3 *
placement in the order Gigartinales. Sequence divergence between these two genera, 3.6%, is comparable with the values of (0.8-)2.8-6.8% noted for genera in the Gracilariales (Bird et al., 1992), and confirms the value of this sequence in characterizing rhodophycean genera. Scholfield et al.. (1991) have reported that intergeneric variation in the 18S rDNA sequences of some red algae can be manifested in restriction-fragmentlength polymorphisms, which in favorable circumstances offer an alternative to the laborious process of sequence analysis in distinguishing related genera and perhaps also species. At present, it is unknown how much this sequence will vary among populations of these species. Ecophenes are known for all the species, and genetic mutants have been identified for some. Chondrus crispus, for example, displays a wide range of morphologies that may be environmental (e.g., Gutierrez & Fernandez, 1992) or genetic (Chen & Taylor, 1980). In the latter case, intersterility of some populations argues that speciation, or at least genetic isolation, is occurring. Genetic isolation probably also occurs in the freeliving forma aegagropila of F. lumbricalis, which reproduces only vegetatively (Bird, Saunders & McLachlan, 1991), and may occur in free-living populations of A.plicata as well (Norton & Mathieson 1981). In P. palmata, dwarf mutants have been observed to differ chemically as well as morphologically from normal populations (Laycock et al., 1989; Laycock & Bird, unpubl.), signifying probable genetic divergence that may be maintained by the apparent sterility of such forms (Bird, unpubl.) . However, our experience with algae of the agarophyte order Gracilariales (Bird et al., 1992) in-
dicates that little variation may be expected in the 18S rDNA sequence of a biological species or perhaps even among congeneric species of similar vegetative and reproductive morphology. We observed sequence variation of 0.35% (6 differences per 18S) in geographically diverse populations of Gracilariaverrucosa (Hudson) Papenfuss, and 0.52% (9 differences per 18S) among European populations of Gracilariopsissp., presumed to represent a single species (M. Steentoft, pers. comm.) although crossability studies have not yet been conducted. Moreover, among G. verrucosa and two other species of Gracilariawith similar reproductive morphology (Verrucosa-type spermatangia, therefore in subgenus Gracilaria), sequence variation was about the same as within G. verrucosa itself. We also have observed that 18S rDNA sequences of P. palmata and a species of the related, structurally and reproductively similar genus Devaleraea are virtually identical (Rice et al., 1991). Thus, differences in excess of these values among morphotypes presently assigned to C. crispus and others would be noteworthy. Although variations in morphology, physiology and chemistry may increase the commercial value of individual strains of these seaweeds, such variation would generally not lie beyond the bounds of species and probably would not be strongly reflected in the 18S rDNA sequences.
Acknowledgements We thank Dr R.K. Singh and Mr T. Parsons for laboratory assistance, and Ms C. Tetu for collecting the sample of Furcellaria lumbricalis. The
384 manuscript benefited from suggestions by Drs M.E. Reith, R.K. Singh, and D.F. Spencer.
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complete sequences of small ribosomal subunit RNA. J. mol. Evol. 32:167-177. Laycock MV, de Freitas ASW, Wright JLC (1989) Glutamate agonists from marine algae. J. appl. Phycol. 1: 113-122. Lim B-Y, Kawai H, Hori H, Osawa S (1986) Molecular evolution of 5S ribosomal RNA from red and brown algae. Jpn. J. Genet. 61: 169-176. Maggs CA, McLachlan JL, Saunders GW (1989) Infrageneric taxonomy of Ahnfeltia (Ahnfeltiales, Rhodophyta). J. Phycol. 25: 351-368. Medlin LK, Elwood HJ, Stichel S, Sogin ML (1991) Morphological and genetic variation within the diatom Skeletonema costatum (Bacillariophyta): evidence for a new species, Skeletonema pseudocostatum. J. Phycol. 27: 514-524. Norton TA, Mathieson AC (1983) The biology of unattached seaweeds. In Round FE, Chapman DJ (eds), Progress in Phycological Research 2. Elsevier Science Publishers BV, Amsterdam, 333-386. Olsen JL (1990) Nucleic acids in algal systematics. J. Phycol. 26: 209-214. Rice EL, Bird CJ (1990) Relationships among geographically distant populations of Gracilaria verrucosa (Gracilariales, Rhodophyta) and related species. Phycologia 29: 501-510. Rice EL, Bird CJ, Murphy CA, Ragan MA (1991) Relationships in three orders of Rhodophyta as revealed by DNA sequences. Abstract, 4th International Phycological Congress, Durham, NC, 4-10 Aug. 1991. J. Phycol. 27(3; suppl.): 62. Scholfield CI, Gacesa P, Price JH, Russell SJ, Bhoday R (1991) Restriction fragment length polymorphisms of enzymically-amplified small-subunit rRNA-coding regions from Gracilariaand Gracilariopsis(Rhodophyta) - a rapid method for assessing 'species' limits. J. appl. Phycol. 3: 329-334.
