Genetic population structure of the monogenean parasite Gyrodactylus thymalli and its host European grayling (Thymallus thymallus) in a large Norwegian lake

Abstract

Understanding how populations are structured in space and time is a central question in evolutionary biology. Parasites and their hosts are assumed to evolve together, however, detailed understanding of mechanisms leading to genetic structuring of parasites and their hosts are lacking. As a parasite depends on its host, studying the genetic structure of both parasite and host can reveal important insights into these mechanisms. Here, genetic structure of the monogenean parasite Gyrodactylus thymalli and its host the European grayling (Thymallus thymallus) was investigated in 10 tributaries draining into the large Lake Mjøsa in Norway. The population genetic structure of spawning grayling was studied using microsatellite genotyping, while G. thymalli was studied by sequencing a mitochondrial DNA gene (dehydrogenase subunit 5). Two main genetic clusters were revealed in grayling, one cluster comprising grayling from the largest spawning population, while the remaining tributaries formed the second cluster. For both taxa, some genetic differentiation was observed among tributaries, but there was no clear isolation-by-distance signature. The structuring was stronger for the host than for the parasite. These results imply that moderate to high levels of gene flow occur among the sub-populations of both taxa. The high parasite exchange among tributaries could result from a lack of strong homing behavior in grayling as well as interactions among individual fish outside of the spawning season, leading to frequent mixing of both host and parasite.

An insight into the functional genomics and species classification of Eudiplozoon nipponicum (Monogenea, Diplozoidae), a haematophagous parasite of the common carp Cyprinus carpio

“…They are also the most host-speci c parasites among atworms [10,11,48]. High host-speci city correlates with unique morphological characteristics of their attachment organs and hooks, which goes hand in hand with molecular markers (e.g., sequences of 28S rRNA, ITS1, cox1, mitochondrial genome) used in species classi cation [49][50][51], and identi cation of genetic population structures [19][20][21]. Despite better accessibility of modern sequencing methods, whole genome sequencing projects targeting monogeneans are limited to the genomes of three other monogenean representatives.…”

“…The Monogenea class is indisputably the most diverse group within the obligate parasitic superclass Neodermata and a better understanding of monogeneans is key to deciphering the evolution of parasitism in atworms [14][15][16]. Monogeneans tend to be studied in terms of phylogenetics [17,18] and population characteristics [19][20][21]. The number of comprehensive molecular analyses of monogeneans is increasing rather slowly: since the last summarisation in late 2020 [22], only one new experimental omics work has been published [23].…”

A paradoxical bias in knowledge about Norwegian freshwater fishes: research efforts during 1980-2020

“…The grayling is host to the monogenean parasite Gyrodactylus thymalli Zitnan, 1960, and this parasite is of great interest as it is very similar to the pathogenic G. salaris (Fromm et al 2014, Mieszkowska et al 2018. Some work has been done on the biology of G. thymalli (Pettersen et al 2015, Pettersen et al 2021, but clearly more work should be done.…”

An insight into the functional genomics and species classification of Eudiplozoon nipponicum (Monogenea, Diplozoidae), a haematophagous parasite of the common carp Cyprinus carpio

“…As demonstrated by a number of studies [ 15 – 18 ], the Monogenea class is, in terms of its molecular, structural, and functional characteristics, probably the most diverse group within the obligate parasitic superclass Neodermata, and a better understanding of monogeneans is key to deciphering the evolution of parasitism in flatworms. Monogeneans tend to be studied in terms of phylogenetics [ 19 , 20 ] and population characteristics [ 21 – 23 ]. The number of comprehensive molecular analyses of monogeneans is increasing rather slowly: since the last summarisation in late 2020 [ 24 ], only one new experimental omics work has been published [ 25 ].…”