Abstract
BackgroundLake Tanganyika is the world’s second deepest lake. Its diverse cichlid assemblage offers a unique opportunity for studying a deep-water host-parasite model in freshwater. Low host specificity and a broad host range including representatives of the Bathybatini tribe in the only monogenean parasite described from this habitat, Cichlidogyrus casuarinus Pariselle, Muterezi Bukinga & Vanhove, 2015 suggest a link between lower specificity and lower host density. Conversely, high host specificity and species richness are reported for monogeneans of the lake’s littoral cichlids. We further investigated whether the deep-water environment in Lake Tanganyika is really monogenean species-depauperate by investigating the monogenean fauna of Trematocara unimaculatum (a representative of the tribe Trematocarini, the sister lineage of the Bathybatini) and Benthochromis horii, a member of the tribe Benthochromini, found in the same deep-water habitat as the already known hosts of C. casuarinus.MethodsSclerotised structures of the collected monogenean individuals were characterised morphologically using light microscopy and morphometrics.ResultsBoth examined cichlid species are infected by a single monogenean species each, which are new to science. They are described as Cichlidogyrus brunnensis n. sp., infecting T. unimaculatum, and Cichlidogyrus attenboroughi n. sp., parasitising on B. horii. Diagnostic characteristics include the distal bifurcation of the accessory piece in C. brunnensis n. sp. and the combination of long auricles and no heel in C. attenboroughi n. sp. In addition C. brunnensis n. sp. does not resemble C. casuarinus, the only species of Cichlidogyrus thus far reported from the Bathybatini. Also Cichlidogyrus attenboroughi n. sp. does not resemble any of the monogenean species documented from the pelagic zone of the lake and is among the few described species of Cichlidogyrus without heel.ConclusionsAs two new and non-resembling Cichlidogyrus species are described from T. unimaculatum and B. horii, colonisation of the deep-water habitat by more than one morphotype of Cichlidogyrus is evident. Based on morphological comparisons with previously described monogenean species, parasite transfers with the littoral zone are possible. Therefore, parasites of pelagic cichlids in the lake do not seem to only mirror host phylogeny and the evolutionary history of this host-parasite system merits further attention.
Highlights
Lake Tanganyika is the world’s second deepest lake
To further our knowledge of the monogenean diversity in deep-water Tanganyika cichlids, we examined Trematocara unimaculatum Boulenger, 1901, a representative of the tribe Trematocarini, the sister group of the Bathybatini [34, 40], and Benthochromis horii Takahashi, 2008, a cichlid species belonging to another deep-water tribe, Benthochromini, which is only distantly related to the Bathybatini [31, 34], but found in the same habitat as the previously reported hosts of C. casuarinus
Trematocara unimaculatum and B. horii were each infected by a single different monogenean species belonging to Cichlidogyrus
Summary
Lake Tanganyika is the world’s second deepest lake. Its diverse cichlid assemblage offers a unique opportunity for studying a deep-water host-parasite model in freshwater. The Monogenea van Beneden, 1858 is a group of mostly ectoparasitic flatworms described mainly from freshwater fishes and phylogenetically closely related to Cestoda van Beneden, 1849 [18, 19] Due to their direct life-cycles and high degree of structural adaptations influenced by host preferences, they are considered as useful targets for investigations focusing on evolutionary processes in parasites [20,21,22,23] as well as for research on the taxonomy [16], biogeography [24,25,26] or phylogeny of their host species [27]. Cichlids display huge species richness and are usually classified into tribes [30]
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