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

Abstract

The effects of introgression on parasitism in brook charr Salvelinus fontinalis were investigated in 28 lakes with various levels of stocking in Québec, Canada. No effect of genetic background on parasitism was found at the individual level. Body length seemed to explain most of the variation observed at this level, with largest fish being more infected. However, lakes with the greater average domestic genetic background were found to display significantly lower parasite prevalence and diversity. Since our results indicate no effect of domestic genes at the individual level, the negative association with introgression found at the population level may be mainly attributed to differences in intrinsic environmental quality of lakes (e.g. fishing pressure, availability of food resources, abiotic characteristics).

Effects of genetic origin on phenotypic divergence in Brook Trout populations stocked with domestic fish

“…The main driver of morphological variation was the lake identity, suggesting that shape of individuals was primarily determined by the characteristics of the population they belonged to. Local environmental differences among lakes, which vary in terms of abiotic (e.g., temperature, dissolved oxygen levels, depth, lake area; Marie et al 2012, Létourneau et al 2018) and biotic conditions (e.g., presence of competitors, parasitic fauna; Gossieaux et al 2018), have been shown to influence morphology (Magnan 1988, Bertrand et al 2008, Baillie et al 2016, Zastavniouk et al 2017). Brook Trout were previously shown to display highly variable morphologies among geographically close lakes (Kazyak et al 2015) and are known to be phenotypically plastic (Kazyak et al 2015, Samways et al 2015, Zastavniouk et al 2017).…”

“…We conducted sampling over two time periods (2007–2008 and 2014–2016) in three wildlife reserves (Portneuf 47°10′7.8″ N, 72°20'32.7″ W, Mastigouche 46°42'45.2″ N, 73°25'37.7″ W, and Saint‐Maurice 47°04′00.0″ N, 73°08′28.5″ W) in Québec, Canada (see Gossieaux et al 2018). Stocking practices are rigorously controlled in these reserves, and stocking history of lakes has been documented since 1964 (provided by the ministère des Forêts, de la Faune et des Parcs, Québec, Canada).…”

“…Moreover, we obtained tissue samples from hatcheries (Jacques Cartier n = 53, Saint‐Alexis des Monts n = 80, Lac des Écorces n = 40) and from lake Bourassa ( n = 40). All protocols and procedures employed were reviewed and approved by the ministère des Forêts, de la Faune et des Parcs (Québec, Canada; see Gossieaux et al 2018, 2019).…”

“…We used adipose fins to extract DNA and genotype each fish at 20 microsatellite loci following the protocols described in Gossieaux et al (2018). We then determined the genetic origin of each fish using the software Structure v. 2.3.4 (Pritchard et al 2000) following the assignment method and parameters described in (Gossieaux et al 2018, 2019). Each fish was attributed a q ‐value ranging from 0 to 1, respectively, designating pure wild and pure domestic individuals.…”

“…We investigated these questions in Brook Trout ( Salvelinus fontinalis ), a very popular salmonid for recreational angling, which has been massively stocked for decades in North America, and notably in Québec, Canada. Previous studies in this region showed that hybridization between domestic and wild fish is common and that stocked lakes present various levels of introgression of domestic genes (Marie et al 2010, 2012, Gossieaux et al 2018, 2019, Létourneau et al 2018). We used data from 12 introgressed populations to determine the extent of phenotypic divergence between individuals that have different genetic origins.…”