title: Shifting Thresholds: Rapid Evolution of Migratory Life Histories in Steelhead/Rainbow Trout, Oncorhynchus mykiss.
abstract: Expression of phenotypic plasticity depends on reaction norms adapted to historic selective regimes; anthropogenic changes in these selection regimes necessitate contemporary evolution or declines in productivity and possibly extinction. Adaptation of conditional strategies following a change in the selection regime requires evolution of either the environmentally influenced cue (e.g., size-at-age) or the state (e.g., size threshold) at which an individual switches between alternative tactics. Using a population of steelhead (Oncorhynchus mykiss) introduced above a barrier waterfall in 1910, we evaluate how the conditional strategy to migrate evolves in response to selection against migration. We created 9 families and 917 offspring from 14 parents collected from the above- and below-barrier populations. After 1 year of common garden-rearing above-barrier offspring were 11% smaller and 32% lighter than below-barrier offspring. Using a novel analytical approach, we estimate that the mean size at which above-barrier fish switch between the resident and migrant tactic is 43% larger than below-barrier fish. As a result, above-barrier fish were 26% less likely to express the migratory tactic. Our results demonstrate how rapid and opposing changes in size-at-age and threshold size contribute to the contemporary evolution of a conditional strategy and indicate that migratory barriers may elicit rapid evolution toward the resident life history on timescales relevant for conservation and management of conditionally migratory species.
authors.affiliation: From the Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060 (Phillis, Moore, and Pearse); Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada (Phillis and Moore); Department of Environmental Science, Policy, & Management, University of California, Berkeley, 130 Mulford Hall, Berkeley, CA 94720 (Buoro); Fisheries Ecology Division, Southwest Fisheries Science Center, National Marine Fisheries Service, 110 Shaffer Rd., Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); Institute of Marine Sciences, University of California, Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); and Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Blvd. East, Seattle, WA 98112 (Phillis). coreyphillis@gmail.com.
authors.forename: Corey C
authors.initials: CC
authors.lastname: Phillis
authors.affiliation: From the Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060 (Phillis, Moore, and Pearse); Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada (Phillis and Moore); Department of Environmental Science, Policy, & Management, University of California, Berkeley, 130 Mulford Hall, Berkeley, CA 94720 (Buoro); Fisheries Ecology Division, Southwest Fisheries Science Center, National Marine Fisheries Service, 110 Shaffer Rd., Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); Institute of Marine Sciences, University of California, Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); and Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Blvd. East, Seattle, WA 98112 (Phillis).
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Moore
authors.affiliation: From the Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060 (Phillis, Moore, and Pearse); Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada (Phillis and Moore); Department of Environmental Science, Policy, & Management, University of California, Berkeley, 130 Mulford Hall, Berkeley, CA 94720 (Buoro); Fisheries Ecology Division, Southwest Fisheries Science Center, National Marine Fisheries Service, 110 Shaffer Rd., Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); Institute of Marine Sciences, University of California, Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); and Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Blvd. East, Seattle, WA 98112 (Phillis).
authors.forename: Mathieu
authors.initials: M
authors.lastname: Buoro
authors.affiliation: From the Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060 (Phillis, Moore, and Pearse); Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada (Phillis and Moore); Department of Environmental Science, Policy, & Management, University of California, Berkeley, 130 Mulford Hall, Berkeley, CA 94720 (Buoro); Fisheries Ecology Division, Southwest Fisheries Science Center, National Marine Fisheries Service, 110 Shaffer Rd., Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); Institute of Marine Sciences, University of California, Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); and Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Blvd. East, Seattle, WA 98112 (Phillis).
authors.forename: Sean A
authors.initials: SA
authors.lastname: Hayes
authors.affiliation: From the Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060 (Phillis, Moore, and Pearse); Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada (Phillis and Moore); Department of Environmental Science, Policy, & Management, University of California, Berkeley, 130 Mulford Hall, Berkeley, CA 94720 (Buoro); Fisheries Ecology Division, Southwest Fisheries Science Center, National Marine Fisheries Service, 110 Shaffer Rd., Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); Institute of Marine Sciences, University of California, Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); and Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Blvd. East, Seattle, WA 98112 (Phillis).
authors.forename: John Carlos
authors.initials: JC
authors.lastname: Garza
authors.affiliation: From the Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060 (Phillis, Moore, and Pearse); Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada (Phillis and Moore); Department of Environmental Science, Policy, & Management, University of California, Berkeley, 130 Mulford Hall, Berkeley, CA 94720 (Buoro); Fisheries Ecology Division, Southwest Fisheries Science Center, National Marine Fisheries Service, 110 Shaffer Rd., Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); Institute of Marine Sciences, University of California, Santa Cruz, CA 95060 (Hayes, Garza, and Pearse); and Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Blvd. East, Seattle, WA 98112 (Phillis).
authors.forename: Devon E
authors.initials: DE
authors.lastname: Pearse
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics*; D025041:Animal Migration; D000818:Animals; D001499:Bayes Theorem; D005075:Biological Evolution; D002140:California; D005260:Female; D005828:Genetics, Population; D005838:Genotype; D008297:Male; D008957:Models, Genetic; D017686:Oncorhynchus mykiss / Q000235:genetics*; D010641:Phenotype; D012641:Selection, Genetic
keywords: alternative migratory tactics; anadromy; conditional strategy; contemporary evolution; partial migration; threshold traits