Gyrodactylus

Esposito, Anaïs, Denys, Gaël P. J., Foata, Joséphine & Quilichini, Yann, 2024, Unclear host taxonomy hinders parasite studies: An up-to-date checklist of the protozoan and metazoan parasites of Phoxinus minnows (Teleostei: Leuciscidae), Journal of Fish Biology 105 (6), pp. 1501-1539 : 1532

4.1 | Gyrodactylus in Phoxinus minnows: Overestimated or underestimated diversity?

Members of the genus Gyrodactylus ( Platyhelminthes: Monogenea) are extremely diverse, viviparous ectoparasites recovered from the fins, gills, and skin of a wide range of fish ( Bakke et al., 2007). P. phoxinus was reported to host the greatest diversity of Gyrodactylus described in any fish species in the Palearctic ( Bakke et al., 2007; Harris et al., 2004; Lumme et al., 2017). In the present bibliographical study, reports concerning 25 Gyrodactylus species were compiled. However, the reassignment of host species showed that this tremendous diversity is the result of taking into account several species of Phoxinus at once.

Some species of Gyrodactylus were only reported from few sampling sites and a few reassigned Phoxinus species, for example, Gyrodactylus albolacustris Lumme et al., 2017 from Russia (reassigned to Phoxinus sp. 7 and P. isetensis ) and Mongolia ( P. ujmonensis ), Gyrodactylus botnicus Lumme et al., 2017 from Finland ( Phoxinus sp. 7 and P. isetensis ), Gyrodactylus danastriae Lumme et al., 2017 from Poland ( P. marsilii ) ( Lumme et al., 2017), Gyrodactylus konovalovi Ergens, 1976 from Russia (either Phoxinus sp. or Rhynchocypris percnurus ) ( Boutorina & Reznik, 2015) or Gyrodactylus llewellyni Ergens & Dulmaa, 1967 from Mongolia ( P. ujmonensis ) ( Ergens & Dulmaa, 1967). Molecular delineation for both Gyrodactylus and their Phoxinus host would help to determine these parasites' host ranges.

Several species have been reported to be more widely distributed, such as G. macronychus on P. phoxinus in the UK, P. cf. morella in Czech Republic, Phoxinus sp. 7 in Finland, Norway, and the UK, P. ujmonensis in Mongolia, P. isetensis in Russia, and P. septimaniae in Spain ( Cruz et al., 2022; Ergens, 1976; Ergens & Dulmaa, 1967; Dorovskikh & Stepanov, 2008; Grano-Maldonado et al., 2011; Matejusová ˇet al., 2000; Pettersen et al., 2016; Ziętara & Lumme, 2003). Such wide ranges of distribution may be the result of (1) cross-countries transfer of hosts and parasite species, (2) a wide host spectrum of these parasites, or (3) undetected cryptic diversity of these parasites on Phoxinus minnows arising from the exclusive use of morphological criteria before the advent of molecular methods. The highest diversity of Gyrodactylus has so far been recorded from Phoxinus sp. 7 , with 13 known species from P. isetensis (10 species), P. ujmonensis (9 species), and P. phoxinus (7 species). No Gyrodactylus were reported from P. csikii and P. lumaireul , which more likely results from Gyrodactylus not being the focus of studies concerning these Phoxinus species than from an absence of Gyrodactylus . Compiled studies regarding P. lumaireul addressed the immunological and cellular response to the infection by the Nematoda Raphidascaris acus (Bloch, 1779) and studies conducted on P. csikii focused on several Platyhelminthes species, mostly D. phoxini . The diversity of Gyrodactylus was thus likely overestimated in P. phoxinus but is most probably underestimated in the genus Phoxinus at the Eurasian scale.

Co-speciation studies would be of interest to explore the common evolutionary history of Gyrodactylus and their Phoxinus hosts and may allow the detection of host-switching or hybridization events. The identification of Gyrodactylus species and haplotypes combined with host-specific determination could furthermore be a useful tool in retracing their hosts' dispersion routes, whether natural or anthropogenic. Parasites, and especially Monogenea, have already been used successfully to gain insights on the historical distribution and routes and vectors of introduction of their host: the origin of Limnothrissa miodon (Boulenger, 1906) ( Clupeidae ) in Lake Kariba, Zimbabwe, was clarified by examining its Kapentagyrus ( Dactylogyridae ) ( Kmentová et al., 2019); contemporary contacts among North American Leuciscidae and historical contact with their European counterparts were revealed through the use of their host-specific Dactylogyridae (Simková ˇet al., 2022); and the lack of Gyrodactylus on the round goby Neogobius melanostomus (Pallas, 1814) allowed Huyse et al. (2015) to suggest an introduction via ballast water for this fish in Belgium.