Molecular study of similar Biomphalaria species

Biomphalaria tenagophila tenagophila; Biomphalaria tenagophila guaibensis; Biomphalaria occidentalis; snails; polymerase chain reaction; polymerase chain reaction restriction fragment length polymorphism; ribosomal RNA

RESEARCH NOTE

Molecular Study of Similar Biomphalaria Species

Vol. 93, Suppl. I: 169-170

Linus Spatz, Teofânia HDA Vidigal*/**, Roberta L Caldeira*, Emmanuel Dias Neto***, Stella Maris González Cappa, Omar S Carvalho*/⁺

Departamento de Microbiología, Facultad de Medicina, Universidad de Buenos Aires, Argentina *Centro de Pesquisas René Rachou-Fiocruz, Av. Augusto de Lima 1715, 30190-002 Belo Horizonte, MG, Brasil **Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil ***Instituto Ludwig de Pesquisas sobre o Câncer, São Paulo, SP, Brasil

Key words: Biomphalaria tenagophila tenagophila - Biomphalaria tenagophila guaibensis - Biomphalaria occidentalis - snails - polymerase chain reaction - polymerase chain reaction restriction fragment length polymorphism - ribosomal RNA

RESEARCH NOTE

Biomphalaria tenagophila tenagophila (Orbigny 1835) is a planorbid susceptible to infection with Schistosoma mansoni which occupies a wide range in South America (WL Paraense 1984 Mem Inst Oswaldo Cruz 79: 465-469) and is an important intermediate host in some areas of Brazil (WL Paraense & L Corrêa 1987 Mem Inst Oswaldo Cruz 82: 577). This species can not be differentiated from B. occidentalis or B. tena-gophila guaibensis by shell characteristics nor morphology of most organs of the genital system (WL Paraense 1981 Mem Inst Oswaldo Cruz 76: 199-211, Paraense 1984 loc.cit.). However only B. t. tenagophila and B. occidentalis are separated by absolute reproductive isolation (Paraense 1981 loc. cit.). So far no reports have been published about reproductive isolation between B. t. tenagophila and B. t. guaibensis or between B. t. guaibensis and B. occidentalis.

The extensive intraspecific heterogeneity in the snails of the genus Biomphalaria at morphological (WL Paraense 1975 Arq Mus Nac RJ 55: 105-128) and genetic levels (THDA Vidigal et al. 1994 Exp Parasitol 79: 187-194), the similarity between species and the small size of some specimens difficult the correct identification of these snails. The PCR-RFLP method (polymerase chain reaction - restriction fragment length polymorphism) has been successfully employed to study genetic variation and identification of species of snails such as Oncomelania hupensis (M Hope & DP McManus 1994 Acta Trop 57: 75-82), Bulinus (JR Stothard et al. 1996 Acta Trop 61: 19-29, JR Stothard & D Rollinson 1997 Trans R Soc Trop Med Hyg 91: 353-357) and more recently by us in Biomphalaria (THDA Vidigal et al. 1998 Exp Parasitol 89: 180-187). Using this approach we analyze here possible sequence polymorphisms in the internal transcribed spacer region (ITS) of the rDNA by PCR amplification and restriction enzymes digestion. The entire ITS was amplified from similar species as B. t. tenagophila, B. t. guaibensis and B. occidentalis using the primers ETTS2 (5^/-TAACAAGGTTTCCGTAGGTGAA-3^/ ) and ETTS1 (5^/-TGCTTAAGTTCAGCGGGT-3^/) anchored respectively in the conserved extremities of the 18S and 28S ribosomal genes (RA Kane & D Rollinson 1994 Mol Bioch Parasitol 63: 153-156).

Studies were undertaken using several snail populations collected from different localities of Brazil, Argentina and Uruguay. Several enzymes were tested (AluI, DdeI, HaeIII, MnlI, HpaII, HfaI, RsaI). Digestion products were separated on 6 or 8% silver stained polyacrylamide gels (CJ Sanguinetti et al. 1994 Biotech 17: 915-918). Our results show that only the restriction profiles obtained after digestion with AluI are capable of identifying the similar species B. t. tenagophila, B. occidentalis and B. t. guaibensis. B. t. tenagophila presented the most heterogeneous profile, showing some polymorphic bands when populations of Brazil and Argentina were compared. The profiles obtained with seven enzymes were used to estimate similarity between these species. A matrix of taxon/character was constructed on the basis of presence/absence of the 70 bands derived from the restriction profiles. The percentage of shared bands was then calculated using the Similarity Coefficient of Dice (LR Dice 1945 Ecol 26: 297-302). These data were then compared by means of UPGMA, unweighted pair group method analysis (PHA Sneath & RR Sokal 1962 Nature 193: 855-860) to generate a dendrogram. The analysis of this dendrogram (Figure) shows that B. t. tenagophila from Brazil and Argentina are clustering separately while the subspecies B. t. guaibensis seems to be more closely related with B. occidentalis than with B. t. tenagophila.

Considering geographical distribution, subspecies concepts (E Mayr et al. 1953 Methods and Principles in Systematic Zoology, McGraw Hill, New York, 328 pp.), similar biological aspects, morphological and molecular similarities between these species we suggest to cluster them into a B. tenagophila complex. However, reproductive isolation experiments should be performed in order to ilucidate this point. The present study shows that PCR-RFLP analysis of the ITS region is a promising approach to investigate the relationships between closely related species of Biomphalaria.

Acknowledgements: to Dr W Lobato Paraense and Dr Lygia Corrêa (Departamento de Malacologia, Instituto Oswaldo Cruz, Rio de Janeiro, RJ) who gave us the snails; to Dr David Rollinson (Natural History Museum, London, UK) for providing the oligonucleotide primers used in this study.

Figure

Work partially supported by Fapemig, Capes, Fiocruz, Conicet and Fundación Roemmeres.

⁺Corresponding author. Fax: [phone]. E-mail: [e-mail]

Received 4 May 1998

Accepted 31 August 1998

Publication Dates

• Publication in this collection
  14 July 2000
• Date of issue
  1998

History

• Accepted
  31 Aug 1998
• Received
  04 May 1998