Ancyrocephalidae ( Monogenea ) of Lake Tanganyika : I : Four new species of Cichlidogyrus from Ophthalmotilapia ventralis ( Teleostei : Cichlidae ) , the first record of this parasite family in the basin

Examination of gill parasites from Ophthalmotilapia ventralis (Boulenger, 1898) in Lake Tanganyika (Africa) revealed the presence of four new species of Monogenea, all members of Cichlidogyrus Paperna, 1960 (Ancyrocephalidae). In view of the systematic importance of haptoral structure, the fish host shows a remarkable diversity of morphological groups. Cichlidogyrus vandekerkhovei sp. nov. and C. makasai sp. nov. are especially characterized by the unusual length of the dorsal transverse bar auricles, while C. sturmbaueri sp. nov. is distinguished by the unique shape of the accessory piece of its male copulatory organ. Importantly, C. centesimus sp. nov. displays a number of features new to the genus, namely a spirally coiled thickening at the end of the penis, the absence of an accessory piece in the genital apparatus, and a hitherto unknown uncinuli configuration in the haptor. This is the first record of ancyrocephalid parasites from the Tanganyika basin. Some mechanisms possibly contributing to this yet unknown diversity are discussed, identifying topics deserving further scientific scrutiny.

Of the three major African Great Lakes (Malawi, Victoria and Tanganyika) Lake Tanganyika is the deepest and the oldest (COHEN et al. 1997).This lake is home to the most morphologically and genetically diverse fauna of Cichlidae in the world (GALIS & METZ 1998, SNOEKS 2000).For non-cichlids, the level of endemicity and the extent to which they evolved into species flocks is highest in this lake (SNOEKS 2000, SALZBURGER et al. 2002).The lake harbours species flocks that result from radiations of several other fish families, such as Mochokidae (DAY & WILKINSON 2006, KOBLMÜLLER et al. 2006) and Mastacembelidae (VREVEN & SNOEKS 2009, BROWN et al. 2010).Various invertebrate taxa, among which platytelphusid crabs (MARIJNISSEN et al. 2006), Gastropoda (MICHEL et al. 2004, WILSON et al. 2004) and Ostracoda (MARTENS & SCHÖN 1999, WOUTERS & MARTENS 2001), also developed species flocks within Lake Tanganyika.POLL (1986) classified the cichlids of Lake Tanganyika into tribes.One of which, the endemic and monophyletic tribe Ectodini, includes species that exhibit a wide range of choices in substrate and food items.Its 34 species, which are classified in 13 genera, are either biparental or maternal mouth-brooders (KONINGS 1998, TAKAHASHI 2003, KOBLMÜLLER et al. 2004, 2008, and references therein).Problems still exist regarding species identification and their respective taxonomical status (HANSSENS et al. 1999).Among these, Ophthalmotilapia Pellegrin, 1904 is paraphyletic and needs taxonomic revision (KOBLMÜLLER et al. 2004).Ophthalmotilapia ventralis (Boulenger, 1898) and O. heterodonta (Poll & Matthes, 1962) form a clade with Cyathopharynx furcifer (Boulenger, 1898), while O. boops (Boulenger, 1901) and O. nasuta (Poll & Matthes, 1962) are sister taxa to each other.
However, despite the great number of studies on Cichlidae of Lake Tanganyika, studies on their parasite fauna, especially on their monogenean flatworms, are practically inexistent as in many tropical biomes throughout the world (WHITTINGTON 1998, BAKKE et al. 2002, HUYSE et al. 2006, VANHOVE et al. 2011).However, monogeneans are known to depict a considerable biological diversity -the average number of species per host is more than six in West Africa (PARISELLE et al. 2003b) -and they usually depict high host specificity, parasitizing a single or few closely related host species.The high host specificity of monogenean species has recently been evidenced by the discovery of extensive cryptic speciation in the group (POUYAUD et al. 2006).Further evidence for the expected high host specificity is provided by the demonstration that the monogenean fauna may help understand the systematics, phylogeny and biogeography of their host groups (EUZET et al. 1989, GUÉGAN & LAMBERT 1990, PAUGY et al. 1990, VAN EVERY & KRITSKY 1992, NIEBERDING & OLIVIERI 2007, PLAISANCE et al. 2008, BARSON et al. 2010).So far, most species of Monogenea recorded from cichlids belong to Cichlidogyrus Paperna, 1960, with 71 currently described species (PARISELLE & EUZET 2009) mostly from West Africa, but also from South and East Africa and West Asia (Levant).
Here, we describe the first representatives of the genus from the Tanganyika basin.In the laboratory, the gills were transferred into clear water in a Petri dish and the monogeneans were detached from these gills using a strong water jet.The worms were individually transferred onto a slide with a mounted needle, directly into a drop of ammonium picrate-glycerine solution (prepared according to MALMBERG 1957), covered with a round cover slip, and sealed with Glyceel (BATES 1997).Some worms from the DRC were mounted between slide and coverslip with Malmberg's solution in the field.Drawings of the sclerotised pieces of the haptor and of the copulatory complex were made using a Leica DM2500 microscope with a camera lucida and a video camera (Leica DFC320).Measurements were obtained with a Leica Application Software v 3.1 and are presented in micrometers with the mean followed by the range and the number of measurements in parentheses.All measurements follow GUSSEV (1962) (Fig. 1).The method of numbering the haptoral parts is that recommended in ICOPA IV (see EUZET & PROST 1981); the terminology of structures follows PARISELLE & EUZET (1995b).PCA analysis was performed using Statistica v. 9 (STATSOFT, INC. 2009).

TAXONOMY
All four new species of Monogenea found on the gills of specimens of O. ventralis belong to Cichlidogyrus Paperna, 1960(according to PAPERNA 1960and PARISELLE et al. 2003a; it should be noted, however, that the absence of an accessory piece in the male copulatory organ (MCO) of C. centesimus sp.nov.might indicate the need for revision of the generic diagnosis).These species are described below.
Remarks.Despite the presence of very long auricles on the dorsal bar, similar in size to the auricles of species of Scutogyrus Pariselle & Euzet, 1995 ( from all these species by the length of the dorsal bar auricles, which are significantly longer (and see below, under C. makasai sp.nov.).
The specific epithet of the new species, vandekerkhovei, honours the aquatic ecologist Dr. Jochen Vandekerkhove (Belgium), in recognition of his guidance during the early research years of the junior author.
The specific name of C. centesimus (Latin for "one hundredth") refers to the fact that the species represents the one-hundredth species described by the senior author (A.P.).
The specific epithet, sturmbaueri, is given in honour of Prof. Christian Sturmbauer (Austria), specialist in the evolution of Tanganyika cichlids and team leader of the expedition in Zambia and Tanzania during which most of the host fish used in this study was caught.

DISCUSSION
Four new representatives of Cichlidogyrus, C. vandekerkhovei sp.nov., C. makasai sp.nov., C. centesimus sp.nov.and C. sturmbaueri sp.nov.are described from Ophthalmotilapia cichlids.The host species are members of the endemic Tanganyika cichlid tribe Ectodini (POLL 1986).Although ancyrocephalids are known to be a speciose lineage of parasites of cichlids (PARISELLE & EUZET 2009) and that Lake Tanganyika is a well-established diversity hotspot of Cichlidae (see SNOEKS 2000), these descriptions represent the first records of Ancyrocephalidae and only the second of Monogenea in this basin (VANHOVE et al. 2011).
The four species described herein belong to three different morphological groups of Cichlidogyrus (PARISELLE & EUZET 2003, 2009, VIGNON et al. 2011).Cichlidogyrus centesimus sp.nov.displays a hitherto unknown combination of characters (and the absence of an accessory piece in the MCO could even indicate the need to revise the generic diagnosis).Hence, based on haptor characteristics, the studied species of Ophthalmotilapia Cichlidogyrus sturmbaueri sp.nov.
In view of the current lack of genetic data and comparative material of Cichlidogyrus spp.from the Tanganyika basin, it is impossible to estimate to what extent the current diversity in haptor morphology actually represents the presence of distinct lineages of Monogenea.Thus, it is not yet appropriate to infer evolutionary scenarios on the origins of the species under study.Rather, we suggest some issues that might deserve closer attention when looking into the parasite diversity on species of Ophthalmotilapia or in the entire basin.
The vagility of the host species is a factor that may potentially influence parasite species richness (GREGORY 1990, MWITA & NKWENGULILA 2008).As O. ventralis is a good disperser, leading to rather unrestrained gene flow (SEFC et al. 2007), it might be interesting to compare its helminth community to the corresponding fauna of host species displaying small-scale geographic population structuring or phylopatric behaviour.Furthermore, the unique ecosystem characteristics of Lake Tanganyika also offer opportunities for a high richness of fish parasites.For instance, ecological stability and depth of the lake facilitate its role as an evolutionary reservoir, such as observed for thalassoid gastropods (WILSON et al. 2004) and cichlids (NISHIDA 1991, SALZBURGER et al. 2002).Therefore, the monogenean community might, partly, consist of ancient lineages as well.Furthermore, KOBLMÜLLER et al. (2006) suggest that the divergence of hosts belonging to the Tropheini influenced differentiation and led to an accelerated rate of molecular evolution of the brood parasite Synodontis multipunctata Boulenger, 1898 (cuckoo catfish) from Lake Tanganyika.Hence, the role of the radiation of Cichlidae in the (co-)evolutionary dynamics of species of Cichlidogyrus should also be considered.
Finally, we want to indicate that the species under study, O. ventralis, apparently shares several parasite species with its congeners, O. boops and O. nasuta.These species of Ophthalmotilapia, although, do not compose a monophyletic group (KOBLMÜLLER et al. 2004).An apparently broad host spectrum in Cichlidogyrus or other representatives of the Monogenea may be the result of cryptic speciation (ZI'TARA & LUMME 2002, HUYSE & MALMBERG 2004, POUYAUD et al. 2006, KUUSELA et al. 2008).Consequently, studies on the new parasite species, based on molecular data, are needed, not only to estimate the extent to which the distinct haptor morphology reflects the existence of various lineages but also to check for possible cryptic speciation leading to an underestimated host-specificity.Furthermore, parasite data from other cichlids in the Tanganyika basin are necessary to formulate hypotheses on the origin and evolutionary history of this seemingly very diverse fauna of monogenean flatworms.

Fish
were caught in April 2008 (Zambia and Tanzania) and April 2010 (Democratic Republic of the Congo (DRC)) using gill or hand nets.Species were determined on site by C. Sturmbauer (Karl-Franzens University of Graz, Austria) and by R. Muzumani (Centre de Recherche en Hydrobiologie, Uvira, DRC).The fishes were dissected, as soon as possible, and the right branchial arches were stored in 96% ethanol for further examination.Fish specimens were numbered, fixed, and preserved in ethanol for subsequent species determination.Additional parasite specimens were collected from O. ventralis hosts captured in Zambia in April 1995 and retrieved from the Royal Museum for Central Africa collections (MRAC 95-96-P-296-301).

Figure 6 .
Figure 6.PCA (first three axes) on all measurements of C. centesimus sp.nov.showing no clusters.
see Fig. 3), C. vandekerkhovei sp.nov. is considered a representative of Cichlidogyrus.Indeed, Scutogyrus spp.have a characteristically enlarged dorsal bar and a thin oval plate associated to the ventral bar (PARISELLE & EUZET 1995a), which are not present in C. vandekerkhovei sp.nov.