Specificity and Specialization of Congeneric Monogeneans Parasitizing Cyprinid Fish

Abstract

Abstract. Patterns and likely processes connected with evolution of host specificity in congeneric monogeneans parasitizing fish species of the Cyprinidae were investigated. A total of 51 Dactylogyrus species was included. We investigated (1) the link between host specificity and parasite phylogeny; (2) the morphometric correlates of host specificity, parasite body size, and variables of attachment organs important for host specificity; (3) the evolution of morphological adaptation, that is, attachment organ; (4) the determinants of host specificity following the hypothesis of specialization on more predictable resources considering maximal body size, maximal longevity, and abundance as measures of host predictability; and (5) the potential link between host specificity and parasite diversification. Host specificity, expressed as an index of host specificity including phylogenetic and taxonomic relatedness of hosts, was partially associated with parasite phylogeny, but no significant contribution of host phylogeny was found. The mapping of host specificity into the phylogenetic tree suggests that being specialist is not a derived condition for Dactylogyrus species. The different morphometric traits of the attachment apparatus seem to be selected in connection with specialization of specialist parasites and other traits favored as adaptations in generalist parasites. Parasites widespread on several host species reach higher abundance within hosts, which supports the hypothesis of ecological specialization. When separating specialists and generalists, we confirmed the hypothesis of specialization on a predictable resource; that is, specialists with larger anchors tend to live on fish species with larger body size and greater longevity, which could be also interpreted as a mechanism for optimizing morphological adaptation. We demonstrated that ecology of host species could also be recognized as an important determinant of host specificity. The mapping of morphological characters of the attachment organ onto the parasite phylogenetic tree reveals that morphological evolution of the attachment organ is connected with host specificity in the context of fish relatedness, especially at the level of host subfamilies. Finally, we did not find that host specificity leads to parasite diversification in congeneric monogeneans.

Evolutionary morphology in shape and size of haptoral anchors in 14 Ligophorus spp. (Monogenea: Dactylogyridae)

“…On the one hand, and as in any other set of organisms, phylogenetic constraints are expected to account for morphological similarity between species. In fact, haptoral morphology has been found to be suitable for inferring phylogenetic relationships in different monogenean taxa [17, 19, 20–22]. On the other hand, the attachment structures of monogeneans are subjected to strong selective pressures.…”

Competition promotes the evolution of host generalists in obligate parasites

“…Selection on parasites to avoid host defences should result in parasites becoming more specialized over time. However, several comparative studies have challenged the idea that host specialization is irreversible (Thompson 1994;Scheffer & Wiegmann 2000;Schluter 2000;Nosil 2002;Poulin et al 2006;Simkova et al 2006). We tested this hypothesis by reconstructing the evolution of host specialization in a large genus of parasitic lice (Phthiraptera), which are obligate vertebrate parasites well known for their host specificity.…”

Biogeographic Hierarchical Levels and Parasite Speciation

“…This helps explain why not every freshwater fish has a Rhabdochona species, and why there are only 8000 species of Digenea, while there are more than 40, 000 species of potential vertebrate hosts to be infected (Hugot et al, 2001). A similar observation was inferred from gyrodactylid phylogenies (Simková et al, 2006;Zietara, & Lumme, 2002).…”