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1. Wild, Native, or Pure: Trout as Genetic Bodies

   https://doi.org/10.1177/0162243920978307  

   Havlick, David G. ; Biermann, Christine ( January 2021 , Science, Technology, & Human Values)

   null (Ed.)

   Advances in genetics and genomics have raised new questions in trout restoration and management, specifically about species identity and purity, which fish to value, and where these fish belong. This paper examines how this molecular turn in fisheries management is influencing wild and native trout policy in Colorado. Examples from two small Colorado watersheds, Bear Creek and Sand Creek, illustrate how framing trout as genetic bodies can guide managers to care for or kill trout populations in the interest of rectifying decades of genetic disruption caused by human activity. While trout management has typically relied on human intervention, the turn to genetic science is prompting new classifications of lineage and taxa, altering long-standing conservation priorities, and reorienting the manipulation of biological processes such as reproduction and dispersal. As a result, other social and ecological factors may be pushed to the margins of management decisions. These changes warrant greater conversation about the consequences of molecular analyses and the values embedded in trout science and conservation more broadly. 

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2. Assessing thermal adaptation using family‐based association and F ST outlier tests in a threatened trout species

   https://doi.org/10.1111/mec.15100  

   Amish, Stephen J. ; Ali, Omar ; Peacock, Mary ; Miller, Michael ; Robinson, Morgan ; Smith, Seth ; Luikart, Gordon ; Neville, Helen ( May 2019 , Molecular Ecology)

   Discovering genetic markers associated with phenotypic or ecological characteristics can improve our understanding of adaptation and guide conservation of key evolutionary traits. The Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) of the northern Great Basin Desert, USA, demonstrated exceptional tolerance to high temperatures in the desert lakes where it resided historically. This trait is central to a conservation hatchery effort to protect the genetic legacy of the nearly extinct lake ecotype. We genotyped full‐sibling families from this conservation broodstock and samples from the only two remaining, thermally distinct, native lake populations at 4,644 new single nucleotide polymorphisms (SNPs). Family‐based genome‐wide association testing of the broodstock identified nine and 26 SNPs associated with thermal tolerance (p < 0.05 andp < 0.1), measured in a previous thermal challenge experiment. Genes near the associated SNPs had complex functions related to immunity, growth, metabolism and ion homeostasis. Principal component analysis using the thermotolerance‐related SNPs showed unexpected divergence between the conservation broodstock and the native lake populations at these loci.F_SToutlier tests on the native lake populations identified 18 loci shared between two or more of the tests, with two SNPs identified by all three tests (p < 0.01); none overlapped with loci identified by association testing in the broodstock. A recent history of isolation and the complex genetic and demographic backgrounds of Lahontan cutthroat trout probably limited our ability to find shared thermal tolerance loci. Our study extends the still relatively rare application of genomic tools testing for markers associated with important phenotypic or environmental characteristics in species of conservation concern.

    

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3. Legacy introductions and climatic variation explain spatiotemporal patterns of invasive hybridization in a native trout

   https://doi.org/10.1111/gcb.13681  

   Muhlfeld, Clint C. ; Kovach, Ryan P. ; Al‐Chokhachy, Robert ; Amish, Stephen J. ; Kershner, Jeffrey L. ; Leary, Robb F. ; Lowe, Winsor H. ; Luikart, Gordon ; Matson, Phil ; Schmetterling, David A. ; et al ( April 2017 , Global Change Biology)

   Hybridization between invasive and native species, a significant threat to worldwide biodiversity, is predicted to increase due to climate‐induced expansions of invasive species. Long‐term research and monitoring are crucial for understanding the ecological and evolutionary processes that modulate the effects of invasive species. Using a large, multidecade genetics dataset (N = 582 sites, 12,878 individuals) with high‐resolution climate predictions and extensive stocking records, we evaluate the spatiotemporal dynamics of hybridization between native cutthroat trout and invasive rainbow trout, the world's most widely introduced invasive fish, across the Northern Rocky Mountains of the United States. Historical effects of stocking and contemporary patterns of climatic variation were strongly related to the spread of hybridization across space and time. The probability of occurrence, extent of, and temporal changes in hybridization increased at sites in close proximity to historical stocking locations with greater rainbow trout propagule pressure, warmer water temperatures, and lower spring precipitation. Although locations with warmer water temperatures were more prone to hybridization, cold sites were not protected from invasion; 58% of hybridized sites had cold mean summer water temperatures (<11°C). Despite cessation of stocking over 40 years ago, hybridization increased over time at half (50%) of the locations with long‐term data, the vast majority of which (74%) were initially nonhybridized, emphasizing the chronic, negative impacts of human‐mediated hybridization. These results show that effects of climate change on biodiversity must be analyzed in the context of historical human impacts that set ecological and evolutionary trajectories.

    

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4. Plastic responses to hot temperatures homogenize riparian leaf litter, speed decomposition, and reduce detritivores

   https://doi.org/10.1002/ecy.3461  

   Jeplawy, Joann R. ; Cooper, Hillary F. ; Marks, Jane ; Lindroth, Richard L. ; Andrews, Morgan I. ; Compson, Zacchaeus G. ; Gehring, Catherine ; Hultine, Kevin R. ; Grady, Kevin ; Whitham, Thomas G. ; et al ( August 2021 , Ecology)

   Efforts to maintain the function of critical ecosystems under climate change often begin with foundation species. In the southwestern United States, cottonwood trees support diverse communities in riparian ecosystems that are threatened by rising temperatures. Genetic variation within cottonwoods shapes communities and ecosystems, but these effects may be modified by phenotypic plasticity, where genotype traits change in response to environmental conditions. Here, we investigated plasticity in Fremont cottonwood (Populus fremontii) leaf litter traits as well as the consequences of plasticity for riparian ecosystems. We used three common gardens each planted with genotypes from six genetically divergent populations spanning a 12°C temperature gradient, and a decomposition experiment in a common stream environment. We found that leaf litter area, specific leaf area, and carbon to nitrogen ratio (C:N) were determined by interactions between genetics and growing environment, as was the subsequent rate of litter decomposition. Most of the genetic variation in leaf litter traits appeared among rather than within source populations with distinct climate histories. Source populations from hotter climates generally produced litter that decomposed more quickly, but plasticity varied the magnitude of this effect. We also found that hotter growing conditions reduced the variation in litter traits produced across genotypes, homogenizing the litter inputs to riparian ecosystems. All genotypes in the hottest garden produced comparatively small leaves that decomposed quickly and supported lower abundances of aquatic invertebrates, whereas the same genotypes in the coldest garden produced litter with distinct morphologies and decomposition rates. Our results suggest that plastic responses to climate stress may constrict the expression of genetic variation in predictable ways that impact communities and ecosystems. Understanding these interactions between genetic and environmental variation is critical to our ability to plan for the role of foundation species when managing and restoring riparian ecosystems in a warming world.

    

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5. Parallel introgression and selection on introduced alleles in a native species

   https://doi.org/10.1111/mec.15097  

   Bay, Rachael A. ; Taylor, Eric B. ; Schluter, Dolph ( June 2019 , Molecular Ecology)

   As humans cause the redistribution of species ranges, hybridization between previously allopatric species is on the rise. Such hybridization can have complex effects on overall fitness of native species as new allelic combinations are tested. Widespread species introductions provide a unique opportunity to study selection on introgressed alleles in independent, replicated populations. We examined selection on alleles that repeatedly introgressed from introduced rainbow trout (Oncorhynchus mykiss) into native westslope cutthroat trout (Oncorhynchus clarkii lewisi) populations in western Canada. We found that the degree of introgression of individual single nucleotide polymorphisms from the invasive species into the native is correlated between independent watersheds. A number of rainbow trout alleles have repeatedly swept to high frequency in native populations, suggesting parallel adaptive advantages. Using simulations, we estimated large selection coefficients up to 0.05 favoring several rainbow trout alleles in the native background. Although previous studies have found reduced hybrid fitness and genome‐wide resistance to introgression in westslope cutthroat trout, our results suggest that some introduced genomic regions are strongly favored by selection. Our study demonstrates the utility of replicated introductions as case studies for understanding parallel adaptation and the interactions between selection and introgression across the genome. We suggest that understanding this variation, including consideration of beneficial alleles, can inform management strategies for hybridizing species.

    

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