Hybridization alters growth and migratory life‐history expression of native trout

Abstract

Human-mediated hybridization threatens many native species, but the effects of introgressive hybridization on life history expression are rarely quantified, especially in vertebrates. We quantified the effects of non-native rainbow trout admixture on important life history traits including growth and partial migration behavior in three populations of westslope cutthroat trout over five years. Rainbow trout admixture was associated with increased summer growth rates in all populations, and decreased spring growth rates in two populations with cooler spring temperatures. These results indicate that non-native admixture may increase growth under warmer conditions, but cutthroat trout have higher growth rates during cooler periods. Non-native admixture consistently increased expression of migratory behavior, suggesting that there is a genomic basis for life history differences between these species. Our results show that effects of interspecific hybridization on fitness traits Accepted Article This article is protected by copyright. All rights reserved can be the product of genotype-by-environment interactions even when there are minor differences in environmental optima between hybridizing species. These results also indicate that while environmentallymediated traits like growth may play an role in population-level consequences of admixture, strong genetic influences on migratory life history differences between these species likely explains the continued spread of non-native hybridization at the landscape-level, despite selection against hybrids at the population-level.

Hybridization decreases native cutthroat trout reproductive fitness

“…Though the rarity of F2 adults in this system limits the potential to statistically demonstrate this pattern, previous studies of hybridization between cutthroat and rainbow trout also support this claim. No study of hybridization between these species has documented the presence of F3 individuals (Baumsteiger et al, 2005; Bay et al, 2019; Boyer et al, 2008; Buehrens et al, 2013; Busack & Gall, 1981; Campbell et al, 2002; Campton & Utter, 1985; Corsi et al, 2013; Docker et al, 2003; Heath et al, 2010; Kovach et al, 2011, 2014; Kozfkay et al, 2007; Loxterman et al, 2014; Metcalf et al, 2008; Muhlfeld et al, 2009; Ostberg et al, 2004; Ostberg & Chase, 2012; Ostberg & Rodriguez, 2006; Pritchard et al, 2015; Rasmussen et al, 2010; Rubidge & Taylor, 2004; Strait et al, 2021; Weigel et al, 2003; Williams et al, 2007; Yau & Taylor, 2013), though this is partially due to the limitations of accurately identifying these hybrid classes with microsatellite markers or small numbers of SNPs. Detecting F3 individuals would also be more difficult if hybrid mate preferences lead to increased backcrossing rather than F2xF2 matings.…”

High dispersal rates in hybrids drive expansion of maladaptive hybridization

“…To quantify the relationship between individual genetic ancestry and adult straying, we estimated individual genetic ancestry from adult mortality samples using 38 species diagnostic single nucleotide polymorphic (SNP) markers that differentiate rainbow trout from westslope cutthroat trout (see [24] for more information). To quantify the relationship between individual genetic ancestry and juvenile migration, we used 3245 genotyped juvenile trout using 650 species diagnostic SNP markers (see [18] for more details). We used different marker panels to estimate genetic ancestry in the straying and migration analysis due to panel availability and laboratory logistics, but both panels use species-diagnostic markers and thus inference is identical; results from [18] are simply more precise.…”

“…To quantify the relationship between individual genetic ancestry and juvenile migration, we used 3245 genotyped juvenile trout using 650 species diagnostic SNP markers (see [18] for more details). We used different marker panels to estimate genetic ancestry in the straying and migration analysis due to panel availability and laboratory logistics, but both panels use species-diagnostic markers and thus inference is identical; results from [18] are simply more precise. For both datasets, the proportion of rainbow trout admixture (pRBT) for each individual was estimated as the number of rainbow trout alleles/2× the number of loci that were genotyped for that individual.…”

“…To quantify the relationship between individual genetic ancestry and adult straying, we estimated individual genetic ancestry from adult mortality samples using 38 species diagnostic single nucleotide polymorphic (SNP) markers that differentiate rainbow trout from westslope cutthroat trout (see [24] for more information). To quantify the relationship between individual genetic ancestry and juvenile migration, we used 3245 genotyped juvenile trout using 650 species diagnostic SNP markers (see [18] royalsocietypublishing.org/journal/rspb Proc. R. Soc.…”

“…Multiple lines of evidence (e.g. patterns in reproductive success and genome-wide patterns of natural selection) demonstrate that natural selection acts against rainbow trout and their hybrids in various environments [4,[6][7][8]17,18]. For example, phenotypic traits associated with fitness [4] and life history [18] show strong evidence for the reduced fitness of trout with non-native genetic admixture compared to native cutthroat trout.…”