Monogenean parasites of cichlids: model systems for speciationand invasion biology?
2014
The stunning diversity of cichlid fishes (Cichlidae) has
greatly enhanced our understanding of speciation and adaptive
radiation. In contrast, little is known about the evolution of
the parasites that infect cichlid species. The enormous
diversity of Lake Tanganyika with its cichlid and non-cichlid
fish species flocks and its importance as cradle and reservoir
of ancient fish lineages seeding other radiations, has resulted
in a significant body of literature in the fields of
biodiversity and evolution. The lake also harbours various
invertebrate taxa that underwent radiation in situ. Remarkably,
until recently virtually no research was carried out into the
Tanganyika parasite fauna. Parasitism is the most common
lifestyle on Earth in terms of species diversity, and it is
established in speciation biology that parasites are prone to
radiate. Hence, parasitic organisms seem a high-potential
subject for speciation studies in ancient lakes. We explore the
diversity and speciation of the “species flock” of monogenean
flatworms infecting Tanganyika cichlids. Monogenea was chosen
because of the species richness and host-specificity of its
representatives. Their simple (one-host) life cycle ensures a
tight association with the respective host species. Therefore,
these parasites constitute prime “markers” for coevolutionary
processes and host taxonomy and evolution. We set off focusing
on the endemic cichlid tribe Tropheini. Combining molecular
sequence data (various portions of the nuclear ITS rDNA,
mitochrondrial cox1) and morphological identification (using
hard parts of attachment and copulatory organs), we discovered
high host-specificity in monogeneans belonging to Cichlidogyrus
(Dactylogyridae) parasitizing tropheines. Phylogenetic
congruence between the flatworm and cichlid phylogeny may be
caused by concomitant divergence and cospeciation events, while
some historical host-switches are also apparent. Furthermore,
within-host speciation caused the representatives of this
parasite genus to surpass the species richness of its host
radiation. Investigating other host lineages in Lake Tanganyika
demonstrated that Cichlidogyrus species followed different
speciation pathways in different cichlid tribes, e.g. lacking
the host-specificity found for tropheine parasites. This
expansion to other cichlid tribes underscores the uniqueness of
Lake Tanganyika’s cichlid flock from a parasitological
point-of-view as well, as demonstrated by the discovery of a
putatively new dactylogyrid genus. Apart from the Lake
Tanganyika biodiversity hotspot, several primarily riverine
cichlids of the Congo Basin are important to fisheries,
aquaculture and aquaristics. We recently started exploring
their monogenean fauna as well. The aim is to investigate the
potential of these parasites as a threat and a tool in
introduced alien species research: the risk of introduction of
non-native monogeneans into the Congo with (Nile) tilapia
introductions, and the potential of monogeneans in stock
identification. We will outline the strategy of this research
project, combining barcoding and marker optimization with the
reconstruction of historical parasite communities. This
research is supported by the Czech Science Foundation
P505/12/G112 (ECIP), the Austrian Science Fund (FWF), the
Research Foundation – Flanders (FWO– Vlaanderen), the King
Leopold III Fund for Nature Conservation and Exploration, and
the Belgian Federal Sciency Policy (BRAIN-be project
BR/132/PI/TILAPIA).
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