Implications of management on immunogenetic variation in the European grayling (Thymallus thymallus)

Abstract

Event Abstract Back to Event Implications of management on immunogenetic variation in the European grayling (Thymallus thymallus) Jana V. Huml1, 2*, Martin Taylor3, W. E. Harris2, Robin Sen2 and Jonathan S. Ellis1 1 University of Plymouth, United Kingdom 2 Manchester Metropolitan University, United Kingdom 3 University of East Anglia, United Kingdom Global-scale ecosystem alteration and current rates of species extinction make the maintenance of biodiversity a major challenge. Genetic diversity is a key parameter for the ability of a species to persist and to adapt to environmental change. This presentation will highlight how genetic research can help inform decisions for management of a salmonid freshwater species (Thymallus thymallus) in the UK (Huml et al., 2018), which is primarily managed through supplementing wild populations with hatchery-reared fish (‘stocking’). This study is the first to characterize functional genetic variation at immune genes within the Major Histocompatibility complex (MHC) in grayling and to assess the effect of stocking on immunogenetic variation in this species. The advantage of directly targeting functional genes is shown. These markers are subject to natural selection and can therefore also tell us about ecologically meaningful variation and evolutionary processes in comparison to neutral non-coding markers. High-throughput Illumina sequencing of three ‘introduced’, four ‘stocked native’ and five ‘non-stocked native’ populations was done to assess genetic variation at the MHC DAA and DAB locus (Huml et al., 2018). These results were compared to microsatellite diversity assessed for the same populations by Dawnay et al. (2011). We observed striking differences in levels of genetic diversity across management classes (‘introduced’, ‘native stocked’ and ‘native non-stocked’ populations) for functional markers (Kruskall-Wallis test: allelic richness, p = 0.007; expected heterozygosity, p = 0.003), but not for non-functional genetic markers (Huml et al., 2018). Introduced populations had the lowest and native non-stocked populations the highest levels of diversity for immune genes. Because immune genetic diversity has implications for pathogen resistance, natural selection frequently maintains levels of immune genetic diversity that are higher than those found at non-functional markers (e.g. Evans and Neff, 2009). This pattern was indeed observed in non-stocked native populations (clustered Mann Whitney-Wilcoxon test: allelic richness, p = 0.008; expected heterozygosity, p = 0.002), but not in the other management classes (Huml et al., 2018). The loss of genetic diversity specific to immune genes within introduced populations can potentially be explained by differences in the pathogen community within the novel environment (Monzón-Argüello et al., 2013). Variants that used to be advantageous in the native habitat may not be beneficial in the new environment and are therefore lost. In order to investigate the potential underlying causes for the observed differences in immune genetic diversity between non-stocked native and stocked native populations we implemented a computer simulation model in SIMUPOP (Peng and Kimmel, 2005). This was designed to specifically test if stocking of hatchery reared fish may affect natural evolutionary processes in populations with different population sizes (Huml et al., 2018). The strongest effects were observed for low population census sizes (500, 750 individuals) and high stocking intensity, where hatchery reared fish exceed in number those naturally produced during one season (Figure 1). Here, both immune genetic and non-functional diversity was lost as a result of stocking (Figure 1). At higher population census sizes (1500, 2000) the loss of diversity was specific to immune genes, which is consistent with our empirical results (Figure 1). This can be explained by the strong reduction in mortality of the vulnerable early life-stages within the hatchery environment. Because this mortality is not completely random in the wild, but partly a result of natural selection, this can impact on the efficiency of evolutionary processes. As evolutionary responses are crucial for the long-term survival of populations, in practical terms, we recommend careful evaluation of whether stocking is the best management option or if natural recruitment can be enhanced, e.g. by the restoration of suitable spawning grounds. As the severity of impacts on immune genetic diversity was strongly dependent on the ratio of naturally produced to stocked fish it is further recommended to assess the rate of natural recruitment and inform the numbers of stocked fish accordingly, where this management option appears necessary. Figure 1: Simulation results (averaged across 100 iterations) are shown for microsatellite and MH observed and expected heterozygosity, averaged across ten years after stocking was implemented for three years at population census sizes of 500, 750, 1500 and 2000, and stocking intensities of 0.5:1, 0.8:1, 1.6:1 and 2:1, representing naturally produced to stocked offspring; significant differences after correction for multiple testing are shown as *** for p-values below 0.001 and ** for p-values below 0.01; Figure 1 Acknowledgements This project was funded by Manchester Metropolitan University and the Grayling Research Trust. The project would not have been possible without the support of the anglers that provided samples for this study. References Dawnay, N., Dawnay, L., Hughes, R.N., Cove, R., Taylor, M.I., 2011. Substantial genetic structure among stocked and native populations of the European grayling (Thymallus thymallus, Salmonidae) in the United Kingdom. Conservation Genetics, 12(3), 731–744. Evans, M.L., Neff, B.D., 2009. Major histocompatibility complex heterozygote advantage and widespread bacterial infections in populations of Chinook salmon (Oncorhynchus tshawytscha ). Molecular Ecology, 18(22), 4716–4729. Huml, J.V., Taylor, M.I., Edwin Harris, W., Sen, R., Ellis, J.S., 2018. Neutral variation does not predict immunogenetic variation in the European grayling (Thymallus thymallus)—implications for management. Molecular Ecology, 27(21), pp.4157-4173. Monzón-Argüello, C., Garcia de Leaniz, C., Gajardo, G., Consuegra, S., 2013. Less can be more: loss of MHC functional diversity can reflect adaptation to novel conditions during fish invasions. Ecology & Evolution, 3(10), 3359–3368. Peng, B., Kimmel, M., 2005. simuPOP: a forward-time population genetics simulation environment. Bioinformatics, 21(18), 3686–3687. Keywords: conservation genetics, Major histocompability complex, Population augmentation, Amplicon sequencing, evolutionary potential Conference: XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019. Presentation Type: Oral Topic: GRAYLING (GENUS THYMALLUS): EVOLUTION, SYSTEMATICS, MANAGEMENT AND CONSERVATION Citation: Huml JV, Taylor M, Harris WE, Sen R and Ellis JS (2019). Implications of management on immunogenetic variation in the European grayling (Thymallus thymallus). Front. Mar. Sci. Conference Abstract: XVI European Congress of Ichthyology. doi: 10.3389/conf.fmars.2019.07.00067 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 10 May 2019; Published Online: 14 Aug 2019. * Correspondence: Dr. Jana V Huml, University of Plymouth, Plymouth, United Kingdom, vanessa.huml@plymouth.ac.uk Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Jana V Huml Martin Taylor W. E Harris Robin Sen Jonathan S Ellis Google Jana V Huml Martin Taylor W. E Harris Robin Sen Jonathan S Ellis Google Scholar Jana V Huml Martin Taylor W. E Harris Robin Sen Jonathan S Ellis PubMed Jana V Huml Martin Taylor W. E Harris Robin Sen Jonathan S Ellis Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.