The role of ecotype‐environment interactions in intraspecific trophic niche partitioning subsequent to stocking

Abstract

Worldwide, stocking of fish represents a valuable tool for conservation and maintenance of species exploited by recreational fishing. Releases of hatchery‐reared fish are more and more recognized to have numerous demographic, ecological, and genetic impacts on wild populations. However, consequences on intraspecific trophic relationships have rarely been investigated. In this study, we assessed the impacts of supplementation stocking and resulting introgressive hybridization on the trophic niches occupied by stocked, local, and hybrid lake trout (Salvelinus namaycush) within populations of piscivorous and planktivorous ecotypes stocked from a wild piscivorous source population. We compared trophic niches using stable isotope analysis (δ13C and δ15N) and trophic position among the three genetic origins. Putative genetic effects were tested with phenotype–genotype association of “life history” ecological traits (body size, growth rate, condition index, and trophic niche) and genotypes (RADseq SNP markers) using redundant discriminant analysis (RDA). Results showed that sympatry resulting from the stocking of contrasting ecotypes is a risk factor for niche partitioning. Planktivorous populations are more susceptible to niche partitioning, by competitive exclusion of the local fish from a littoral niche to an alternative pelagic/profundal niche. Observed niche partitioning is probably a manifestation of competitive interactions between ecotypes. Our results emphasize that ecotypic variation should be considered for more efficient management and conservation practices and in order to mitigate negative impact of supplementation stocking.

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

“…Domestic trout seem to grow larger than wild fish and to monopolize the best quality feeding niches. In other salmonids, stocked domestic fish have been showed to displace wild populations (Morissette et al 2019), possibly because of their size advantage (McGinnity et al 1997). This size advantage of domestic fish appears in early life stages in our results and likely leads to domestics outcompeting wild individuals.…”

“…Carbon and nitrogen stable isotopes ratios quantifications were conducted at the Ján Veizer Stable Isotope Laboratory (University of Ottawa, Ontario, Canada). Detailed procedure is available in Morissette et al (2019). Results are expressed as part per thousand (‰) noted as δ 13 C and δ 15 N.…”

“…Alternatively, if phenotype is mostly shaped by environmental conditions, phenotypic divergence should be small and hybrids should resemble wild individuals since they shared the same environment since hatching. As a complementary question, we used stable isotope analyses to assess whether genetic origin influences habitat use and feeding habits, since these are two essential determinants of morphology (Bourke et al 1997, Dynes et al 1999, Bertrand et al 2008, but see Samways et al 2015, Andersson et al 2017) and growth (Glaz et al 2012, 2014, Morissette et al 2018, 2019).…”

Deciphering lifelong thermal niche using otolith δ18O thermometry within supplemented lake trout (Salvelinus namaycush) populations

“…Biotic variables included in the model were total length (TL, mm), percentage of fish population attributed to stocked genotype ( Q stocked ), C:N ratio (a measure of fat content), trophic position (TP) and Δ Pelagic (contribution of pelagic prey to diet), the last three factors were nested in factor lake. C:N, TP and Δ Pelagic were estimated from white muscle δ 13 C and δ 15 N stable isotope values collected on the same fish (see Morissette, Sirois, Wilson, Laporte, and Bernatchez (2019) for complete methodology). Significance of contributions for every factor was assessed by analysis of variance.…”

Genetic Integrity of Lake Trout in Cold Lake, Alberta, Despite Decades of Supplemental Stocking

“…Subsequent analysis using genomic markers detected significant linkage disequilibrium between approximately 3% of the markers with fitness‐related traits (Morissette et al. ).…”