Hybridization decreases native cutthroat trout reproductive fitness

Abstract

Examining natural selection in wild populations is challenging, but crucial to understanding many ecological and evolutionary processes. Additionally, in hybridizing populations, natural selection may be an important determinant of the eventual outcome of hybridization. We characterized several components of relative fitness in hybridizing populations of Yellowstone cutthroat trout and rainbow trout in an effort to better understand the prolonged persistence of both parental species despite predictions of extirpation. Thousands of genomic loci enabled precise quantification of hybrid status in adult and subsequent juvenile generations; a subset of those data also identified parent–offspring relationships. We used linear models and simulations to assess the effects of ancestry on reproductive output and mate choice decisions. We found a relatively low number of late‐stage (F3+) hybrids and an excess of F2 juveniles relative to the adult generation in one location, which suggests the presence of hybrid breakdown decreasing the fitness of F2+ hybrids later in life. Assessments of reproductive output showed that Yellowstone cutthroat trout are more likely to successfully reproduce and produce slightly more offspring than their rainbow trout and hybrid counterparts. Mate choice appeared to be largely random, though we did find statistical support for slight female preference for males of similar ancestry. Together, these results show that native Yellowstone cutthroat trout are able to outperform rainbow trout in terms of reproduction and suggest that management action to exclude rainbow trout from spawning locations may bolster the now‐rare Yellowstone cutthroat trout.

The optimal stocking strategy for Yaqui Catfish

“…Future collections to build a broodstock of Yaqui Catfish will require a robust design (i.e., probabilistic sampling with respect to hybrid zones) to ensure appropriate development and implementation of effective genetic markers. For example, to quantify variable hybridization outcomes, biologists should sample individuals irrespective of phenotype (including both parental species and potential hybrids) at their natural abundances within random streams found throughout their range, with the goal of producing an estimate of the incidence of hybridization and abundance (see Mandeville et al 2015, 2019; Gompert et al 2017; Rosenthal et al 2022). This approach has never been attempted, nor has any sampling been done in Sonora, Mexico, to detect population abundance or declines using formal sampling methods that account for detection probability.…”

“…Given that hybridization dynamics may vary substantially across locations and time, careful screening for species‐specific loci and adequate diagnostic power is required to ensure that genetic markers provide an accurate assignment of each species, their interspecific hybrids, and overall introgression dynamics (Mandeville et al 2015; Kim et al 2022; Rosenthal et al 2022). Genetic workflows like these are now routine procedures for state and federal fishery programs in the United States to identify and distinguish unadmixed species from hybrids (see Tranah et al 2001, 2004; Schrey et al 2007, 2011; Campbell et al 2015; Lamer et al 2015; Jordan et al 2019; Kim et al 2022; Rosenthal et al 2022). For Yaqui Catfish, the next logical step is to use these genetic tools within an appropriate sampling design to promptly develop appropriate broodstock—before genetically unadmixed Yaqui Catfish disappear—while producing results that can also inform the incidence of hybridization to appropriately characterize its extent throughout the species' range (Campbell et al 2015; Lamer et al 2015; Jordan et al 2019).…”

“…Genetic management Describes genetic considerations for annual monitoring; safeguarding against hybridization; and spawning, rearing, and stocking of Yaqui Catfish goal of producing an estimate of the incidence of hybridization and abundance (see Mandeville et al 2015Mandeville et al , 2019Gompert et al 2017;Rosenthal et al 2022). This approach has never been attempted, nor has any sampling been done in Sonora, Mexico, to detect population abundance or declines using formal sampling methods that account for detection probability.…”

“…Development of a genetic marker set that allows for accurate diagnosis of hybridization and population-level diversity is also needed. Given that hybridization dynamics may vary substantially across locations and time, careful screening for species-specific loci and adequate diagnostic power is required to ensure that genetic markers provide an accurate assignment of each species, their interspecific hybrids, and overall introgression dynamics (Mandeville et al 2015;Kim et al 2022;Rosenthal et al 2022). Genetic workflows like these are now routine procedures for state and federal fishery programs in the United States to identify and distinguish unadmixed species from hybrids (see Tranah et al 2001Tranah et al , 2004Schrey et al 2007Schrey et al , 2011Campbell et al 2015;Lamer et al 2015;Jordan et al 2019;Kim et al 2022;Rosenthal et al 2022).…”

Influence of dams on sauger population structure and hybridization with introduced walleye

“…BC sauger were defined as Q − 2 q between −0.1 and 0.1; BC walleye were defined by Q + 2 q between 1.9 and 2.1. These cut‐offs were selected to be similar to previous work (Mandeville et al., 2019 ; Rosenthal et al., 2022 ) and derived from work on the entropy model evaluating realistic expectations for these values (e.g., Lindtke et al., 2014 ). These classes are broad by necessity due to the effects of genetic variation in parental populations when sampling thousands of loci.…”