DOI: 10.2478/s11686-008-0029-4 © 2008 W. Stefañski Institute of Parasitology, PAS Acta Parasitologica, 2008, 53(2), 133–144; ISSN 1230-2821 In search of mitochondrial markers for resolving the phylogeny of cyclophyllidean tapeworms (Platyhelminthes, Cestoda) – a test study with Davaineidae D. Timothy J. Littlewood1*, Andrea Waeschenbach1 and Pavel N. Nikolov2 1Department of Zoology, Natural History Museum, Cromwell Road, London SW7 5BD, UK; 2Central Laboratory of General Ecology, Bulgarian Academy of Sciences, 2 Gagarin Street, 1113 Sofia, Bulgaria Abstract The most species rich order of tapeworms is the Cyclophyllidea and prior to wide-scale sampling of these worms for phylo- genetics, we wished to develop reliable PCR primers that would capture fragments of mitochondrial (mt) DNA with phyloge- netic utility across the order. Nuclear ribosomal RNA gene sequences are well-established and valuable markers for resolving flatworm interrelationships spanning a wide range of taxonomic divergences, but fail to provide resolution amongst recently diverged lineages. Entire mt genomes of selected cyclophyllidean tapeworms are available on GenBank, and we used these to design PCR primers to amplify mtDNA from cox1, rrnL and nad1 for a range of cyclophyllideans (7 davaineids, 1 hymenole- pidid and 1 dilepidid) and selected outgroups (Tetrabothrius sp. and Mesocestoides sp.). A combined nuclear and mt gene data set was used to estimate a reference phylogeny and the performance of the individual genes was compared to this. Although nuclear and mt genes each contributed to the structure and stability of the phylogenetic estimate, strongest nodal support was provided by nuclear data amongst the basal lineages and by mt data amongst the most recently diverged lineages. The appar- ent complementarity afforded by combining nuclear and mt data was compromised by these data partitions providing conflicting signal at poorly supported nodes. Nevertheless, we argue for a combined evidence approach. PCR primers that amplify rrnL were designed and tested successfully against a diversity of cyclophyllideans; rrnL and nad1 appeared to be more informative than the fragment of cox1. The genus Raillietina was not supported by molecular evidence. The new primers will likely pro- vide considerable resolution to estimates of cyclophyllidean interrelationships in future studies. Keywords mtDNA, phylogeny, Cyclophyllidea, Davaineidae Introduction The family Davaineidae Braun, 1900 is one of the most species-rich groups of cyclophyllideans. According to our es- Of the 17 recognised orders of tapeworm, the most species- timate, it includes about 450 species parasitising mainly birds rich, by far, is the Cyclophyllidea. Some 3,100 described (about 425 species, 127 of which are reported from gallina- species (Georgiev 2003) make this order as diverse in terms of ceous birds) as well as mammals (including 6 species report- species number as the remaining cestode orders combined (in ed from humans). total, ~5,200 cestode species are known). Nevertheless, the Historically, the group was regarded as a family (Fuhr- estimate is likely to represent only a small proportion of the mann 1932, Wardle and McLeod 1952, Yamaguti 1959, true diversity of these tapeworms that infect predominantly Schmidt 1986, Jones and Bray 1994) or a suborder (Artyukh tetrapods (mostly birds and mammals but also amphibians and 1966) including two (Artyukh 1966, Jones and Bray 1994) or reptiles), as many potential hosts and biogeographic provinces three (Fuhrmann 1932; Wardle and McLeod 1952; Yamaguti have remained unsampled. Cyclophyllideans include well- 1959; Schmidt 1986; Movsesyan 2003a, b) subfamilies or known parasites of humans and livestock (e.g. species of Taenia families, respectively. and Echinococcus), but their abundance and wide distribution Among the davaineid genera, the most species-rich is Rail- in the wild suggests they play important roles in all terrestri- lietina Fuhrmann, 1920 with about 190 species reported from al, most limnetic and many coastal ecosystems. birds and mammals (including humans), (Movsesyan 2003a). *Corresponding author: [email protected] 134 D. Timothy J. Littlewood et al. Œl¹ski Fuhrmann (1920) subdivided the genus into four subgenera scored and analysed cladistically, remains the best treatment but it was later subjected to various changes concerning both of the relationships between the families of Cyclophyllidea to the composition and rank of the subordinated taxa (Fuhrmann date. However, with the propensity for many of these features 1924, Stiles and Orleman, cited after Artyukh 1966, López- to evolve convergently, independent molecular phylogenies Neyra 1931, Fuhrmann 1932, Movsesyan 1966). The gener- are much needed in order to bring stability and order to the ally accepted system was that proposed by Fuhrmann (1932) group. Moreover, additional characters are needed to add great- (Wardle and McLeod 1952, Yamaguti 1959, Artyukh 1966, er resolution to the estimates of inter- and intra-familial rela- Schmidt 1986). According to it, the genus Raillietina includ- tionships. ed the subgenera Raillietina Fuhrmann, 1920, Paroniella Fuhr- Building on our previous studies on the molecular sys- mann, 1920, Fuhrmannetta Stiles et Orleman, 1926 and Skrja- tematics of cestodes, we investigated the phylogenetic utility binia Fuhrmann, 1920. The last comprehensive taxonomic of potential gene markers in estimating the interrelationships works on davaineids (Jones and Bray 1994, Movsesyan 2003a) of selected members of a cyclophyllidean family, as a precur- elevated the subgenera of Raillietina to the generic level; this sor to broad-scale sampling and molecular phylogenetic analy- concept is followed in the present study. ses at higher taxonomic levels. To date, commonly used mo- The characters used for distinguishing the taxa at the fam- lecular markers for the Cestoda include complete small sub- ily level were the structure of the uterus and (or) presence of unit and complete and partial large subunit ribosomal RNA paruterine organ, and at the generic level these were the scolex genes, i.e. ssrDNA and lsrDNA, respectively. These genes armament, the position and number of the genital pores per have been used extensively to estimate ordinal level relation- proglottis, the position of the genital organs and, if paruterine ships (Kodedová et al. 2000, Olson et al. 2001, Waeschenbach organ is lacking, the number of the eggs within an egg capsule et al. 2007) and relationships within orders (e.g. Brabec et al. (Wardle and McLeod 1952; Yamaguti 1959; Artyukh 1966; 2006) but hardly amongst cestode families; one order that has Schmidt 1986; Jones and Bray 1994; Movsesyan 2003 a, b). been investigated more than most with these genes is the As a result, the available taxonomy of the Davaineidae is arti- Proteocephalidea (e.g. Hypsa et al. 2005). Additional popular ficial rather than representing the phylogenetic relationships markers include mitochondrial genes such as partial cyto- within the group. The davaineids have never been subjected to chrome oxidase subunit I (cox1; e.g. Hu et al. 2005, Wickström extensive phylogenetic studies on the basis of molecular data. et al. 2005), partial small subunit ribosomal RNA gene rrnS Representatives of two davaineid genera (Raillietina and O- (12S; von Nickisch-Rosenegk et al. 1999) and partial large phryocotyle) were included in analysis on the basis of molec- subunit ribosomal RNA gene rrnL (16S; Zehnder and Ma- ular data to study the interordinal phylogenetic relationships riaux 1999), which have been used with varying success for of the cestodes (Mariaux 1998). The few proposed hypotheses within order/family phylogenetic resolution and the recogni- within the order Cyclophyllidea did not include davaineids tion of cryptic taxa. Preliminary analyses with cyclophylli- (von Nickisch-Rosenegk et al. 1999) or gave controversial re- deans (Tkach and Littlewood, unpublished) suggest that genes sults for their relationships with other cyclophyllidean groups evolving faster than the nuclear ribosomal genes used so far (Foronda et al. 2004). are required to differentiate more recent divergence events. In summary, the family Davaineidae was chosen as a mod- However, rather than choosing from the limited number of el group for several reasons. First, it is a speciose family with available PCR primer combinations, of which few appear to controversial classification. The genus Raillietina and related hold much promise (Olson and Tkach 2005), we have decided genera form a compact and morphologically homogeneous to evaluate a rich resource of orthologous genes and gene group (e.g., the genera Raillietina and Fuhrmannetta could be regions, from available completed mitochondrial (mt) ge- distinguished by the position of genital pores: unilateral in the nomes. former and irregularly alternating in the latter), thus repre- Interest in comparative mitogenomics and mt genomes, as senting a suitable model taxon for testing the reliability of a source of molecular markers in flatworms of biomedical and morphological criteria by molecular phylogenetic evidence. economic importance (e.g. see Le et al. 2002, Johnston 2006), In particular, the Raillietina spp. from woodpeckers provide has resulted in a number of completed mt genomes being fully a good opportunity to test the phylogenetic relatedness of par- characterized for key cyclophyllidean taxa. Currently on Gen- asites from resident hosts in Europe and North America. Sec- Bank there are