Parental genetic diversity of brown trout (Salmo trutta m. fario) brood stock affects offspring susceptibility to whirling disease

Abstract

BackgroundWhirling disease, caused by the myxozoan parasite Myxobolus cerebralis, has high economical and ecological importance worldwide. Susceptibility to the disease varies considerably among salmonid species. In brown trout (Salmo trutta) the infection is usually subclinical with low mortality, which increases the risk of parasite dissemination, especially when farm fish are used for stocking natural habitats. The influence of intraspecific genetic differences (especially the level of homozygosity) on susceptibility is unknown. Therefore, we examined the possible correlations between parental genetic diversity and offspring susceptibility of brown trout stocks to whirling disease.MethodsTwo brown trout brood stocks from a German and a Hungarian fish farm were genetically characterized using microsatellite and lineage-specific genetic markers. The individual inbreeding coefficient f and pairwise relatedness factor r were estimated based on eight microsatellite markers. Brood stock populations were divided into groups according to low and high f and r value estimates and subjected to selective fertilization. The offspring from these separate groups were exposed to M. cerebralis actinospores, and the infection prevalence and intensity was measured and statistically analysed.ResultsThe analysis of phylogeographic lineage heritage revealed high heterogeneity in the Hungarian brood stock since > 50% of individuals were Atlantic-Danubian hybrids, while only pure Atlantic-descending specimens were detected in the German population. Based on fmsat and rmsat estimations, classified non-inbred (NIB), inbred (IB) and a group of closely related fish (REL) were created. The susceptibility of their offspring varied considerably. Although there was no significant difference in the prevalence of M. cerebralis infection, the mean intensity of infection differed significantly between NIB and IB groups. In REL and IB groups, a high variability was observed in infection intensity. No external clinical signs were observed in the exposed brown trout groups.ConclusionsOur findings indicate that the allelic diversity of brown trout brood stock may constitute a significant factor in disease susceptibility, i.e. the intensity of parasite infection in the subsequent generation.

Effects of Inbreeding on Genetic Characteristic, Growth, Survival Rates, and Immune Responses of a New Inbred Line of Exopalaemon carinicauda

“…Inbred mating within a closed, small population tends to accelerate the loss of gene diversity and reduce the heterozygosity of genes in a population, ultimately leads to complete homozygosity observed from molecular markers [14]. Inbreeding also results in a decline in the mean phenotypic values of some traits, mainly including those related to fitness and physiological efficiency in normal outbreeding species, which is known as inbreeding depression [15,16].…”

Myxozoan polar tubules display structural and functional variation

“…Although many have established benign, asymptomatic relationships with their hosts, some species cause devastating diseases of both natural and farmed fish populations. These diseases, including proliferative kidney disease, enteromyxosis and whirling disease, have severe ecological and economic impacts [ 9 – 13 ]. Most myxozoans are in the class Myxosporea and, for those whose life cycle has been elucidated, it involves alternation between two hosts, namely a vertebrate, usually a fish, and an invertebrate, currently known to be annelids [ 14 – 16 ].…”

Introgressive hybridization between wild and domestic individuals and its relationship with parasitism in brook charrSalvelinus fontinalis

“…A lower parasitism in stocked lakes could be partly due to the higher genetic diversity that is typical of stocked S. fontinalis in Québec (Marie et al ., ). Indeed, a high genetic diversity is considered an important component of disease and parasite resistance (Coltman et al ., ; Eszterbauer et al ., ). Moreover, parasites can sometimes have a reduced infection success when they are confronted to non‐local hosts (Kalbe et al ., ; Voutilainen et al ., ).…”