Systematics of Mesocestoides (Cestoda: Mesocestoididae): Evaluation of Molecular and Morphological Variation Among Isolates
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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications from the Harold W. Manter Laboratory of Parasitology Parasitology, Harold W. Manter Laboratory of 2005 SYSTEMATICS OF MESOCESTOIDES (CESTODA: MESOCESTOIDIDAE): EVALUATION OF MOLECULAR AND MORPHOLOGICAL VARIATION AMONG ISOLATES Kerry A. Padgett California Department of Health Services, [email protected] Steven A. Nadler University of California - Davis, [email protected] Linda Munson University of California - Davis Ben Sacks University of California - Davis Walter M. Boyce University of California - Davis, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/parasitologyfacpubs Part of the Parasitology Commons Padgett, Kerry A.; Nadler, Steven A.; Munson, Linda; Sacks, Ben; and Boyce, Walter M., "SYSTEMATICS OF MESOCESTOIDES (CESTODA: MESOCESTOIDIDAE): EVALUATION OF MOLECULAR AND MORPHOLOGICAL VARIATION AMONG ISOLATES" (2005). Faculty Publications from the Harold W. Manter Laboratory of Parasitology. 713. https://digitalcommons.unl.edu/parasitologyfacpubs/713 This Article is brought to you for free and open access by the Parasitology, Harold W. Manter Laboratory of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications from the Harold W. Manter Laboratory of Parasitology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Padgett, Nadler, Munson, Sacks & Boyce in Journal of Parasitology (2005) 91(6). Copyright 2005, American Society of Parasitologists. Used by permission. J. Parasitol., 91(6), 2005, pp. 1435±1443 q American Society of Parasitologists 2005 SYSTEMATICS OF MESOCESTOIDES (CESTODA: MESOCESTOIDIDAE): EVALUATION OF MOLECULAR AND MORPHOLOGICAL VARIATION AMONG ISOLATES Kerry A. Padgett*, Steven A. Nadler², Linda Munson, Ben Sacks³, and Walter M. Boyce Department of Veterinary Pathology, Microbiology, and Immunology, University of California, One Shields Avenue, Davis, California 95616. e-mail: [email protected] ABSTRACT: A hypothesis-based framework was used to test if 3 genetic strains of Mesocestoides (clades A, B, and C) are distinct evolutionary lineages, thereby supporting their delimitation as species. For comparative purposes, 3 established cestode species, Taenia pisiformis, Taenia serialis, and Taenia crassiceps were assessed using the same methods. Sequence data from mitochon- drial rDNA (12S) and the second internal transcribed spacer of nuclear rDNA (ITS-2) revealed derived (autapomorphic) characters for lineages representing clade A (n 5 6 autapomorphies), clade B (n 5 4), and clade C (n 5 9) as well as T. pisiformis (n 5 15) and T. serialis (n 5 12). Furthermore, multivariate analysis of morphological data revealed signi®cant differences among the 3 genetic strains of Mesocestoides and between T. pisiformis and T. serialis. The level of phenotypic variation within evolutionary lineages of Mesocestoides and Taenia spp. tapeworms was similar. Results from this study support recognizing Mesocestoides clades A, B, and C as separate species, and provide evidence that clade B and Mesocestoides vogae are conspeci®c. Traditionally, parasite species have been described using the proach to delimiting species allows for hypothesis testing and Linnaean or similarity species concept, which is based primarily potential refutation. For example, Nadler et al. (2000) used this upon differences in morphological characteristics or host iden- theoretical framework to evaluate Uncinaria spp. hookworms tity (Mayr, 1963). Although this species concept and its meth- from 2 sympatric host species (California sea lions, Zalophus ods have proven useful for delimiting species of many macro- californianus, and northern fur seals, Callorhinus ursinus, col- parasites, it has been unsuccessful for certain other common lected from San Miguel Island, Channel Island National Park). parasites, including Mesocestoides spp. tapeworms, because of They found that hookworms from each host species had auta- dif®culties presented by morphological plasticity or, conversely, pomorphies characteristic of separate evolutionary lineages, in- cryptic species. Identi®cation and species delimitation of Me- dicating that each pinniped species hosted distinct hookworm socestoides spp. tapeworms is dif®cult because of con¯icts species. among key morphological characters (Loos-Frank, 1987) and a Recent molecular phylogenetic studies of Mesocestoides spp. high degree of host-induced nonspeci®c morphological varia- revealed at least 3 distinct monophyletic groups (clades A, B, tion (Rausch, 1994). For example, Voge (1955) examined 6 and C) in western North America (Crosbie et al., 1998, Crosbie, putative Mesocestoides species from North America and con- Nadler et al., 2000, Crosbie, Padgett et al., 2000). Clade A cluded that the high degree of morphological variability war- included acephalic metacestodes and adult tapeworms from ranted a complete revision of the genus. Furthermore, adult Me- dogs and coyotes, respectively. Clade B was composed of te- socestoides spp. with similar genetic characteristics have been trathyridia from a dog and a western fence lizard (Sceloporus isolated from a wide host and geographic range (Crosbie, Nadler occidentalis), and clade C was composed of adult tapeworms et al., 2000; Crosbie, Padgett et al., 2000; Padgett and Boyce, from dogs. Although these studies showed Mesocestoides spp. 2004), thus indicating that there is reduced speci®city for ®nal isolates belong to separate clades, evolutionary species delim- hosts in some species of this genus. Clearly, Mesocestoides is itation would bene®t from population-level sampling of indi- a particularly problematic genus, but more broadly, there is lim- viduals and analysis of multiple genetic loci. ited value in using only similarity measures for delimiting par- Compared to Mesocestoides, the species-level systematics of asite species. Because efforts to distinguish among Mesocestoides species taeniid tapeworms is better resolved. Based on morphological using morphological similarities have often failed, other ap- analysis of adult specimens, there are approximately 40 rec- proaches are needed. In an attempt to reduce the systematic ognized species in the genus Taenia (Hoberg et al., 2000). error in nematode species delimitation, Adams (1998) recom- Many recent studies have shown high levels of interspeci®c mended an amalgamation of phylogenetic species concepts variation for molecular characters that are useful for distin- (e.g., Cracraft, 1983) and evolutionary species concepts (e.g., guishing species of Taenia (Bowles and McManus, 1994; Gas- Wiley, 1978). Using this methodology, species are recognized ser and Chilton, 1995; De Queiroz and Alkire, 1997; Nickisch- based upon evidence of independent evolutionary lineages re- Rosenegk et al., 1999). Because of the comparatively advanced ¯ected in the form of autapomorphies, i.e., derived character state of species-level taeniid systematics, Taenia species pro- states unique to individuals of a species. This phylogenetic ap- vide a good standard for comparative analysis with other prob- lematic cestode species such as Mesocestoides. The objectives of this study were (1) to determine whether Received 9 July 2004; revised 29 March 2005; accepted 29 March Mesocestoides clades A, B, and C are distinct evolutionary lin- 2005. * Present address: Vector-Borne Disease Section, California Department eages that should be delimited as separate species; (2) to de- of Health Services, 850 Marina Bay Parkway, Richmond, California termine whether established species of Taenia show evidence 94804. of lineage independence using the same genetic loci and meth- ² Department of Nematology, University of California, One Shields Av- ods; and (3) to assess the extent of morphological variation enue, Davis, California 95616. ³ Veterinary Genetics Laboratory, School of Veterinary Medicine, Uni- among and within each clade of Mesocestoides and each species versity of California, One Shields Avenue, Davis, California 95616. of Taenia. 1435 1436 THE JOURNAL OF PARASITOLOGY, VOL. 91, NO. 6, DECEMBER 2005 MATERIALS AND METHODS were performed on 2 gene fragments. A 314-bp fragment of mitochon- drial 12S rDNA was ampli®ed using cestode-speci®c primers 60.for. Primary characterization of samples (59-TTAAGATATATGTGGTACAGGATTAGATACCC-39) and 375. With the exception of specimens acquired from museum or personal REV. (59-AACCGAGGGTGACGGGCGGTGTGTACC-39) (Nickisch- collections (certain Mesocestoides spp., T. pisiformis, and T. serialis), Rosenegk et al., 1990). As previously reported (Gasser and Chilton, all tapeworm specimens used in this study were identi®ed in the fol- 1995; Crosbie et al., 1998), ampli®cation of a 600±700-bp region of lowing manner. Metacestode and adult tapeworm samples were identi- ITS-2 nuclear rDNA was accomplished using primers NC-6 (59-ATC ®ed to genus using morphological characters. Because many Mesoces- GACATCTTGAACGCACATTGC-39) and NC-2 (59-TTAGTTTCTTT toides spp. metacestodes from domestic dogs lack apical suckers (``ace- TCCTCCGCT-39). Total volume for PCR reactions was 100 ml, com- phalic metacestodes''), morphological identi®cation of these specimens prising 20 ml of DNA extract, 54.6 ml of sterile water, 5 ml of each m m m was not possible. Instead, all tapeworms were tested independently by primer, 2 l of 10 mM dNTP mix, 10 l 10x PCR buffer, 3.0 l MgCl2 a PCR±RFLP assay targeting the second internal transcribed