Human‐mediated evolution in a threatened species? Juvenile life‐history changes in Snake River salmon

Abstract

Evaluations of human impacts on Earth's ecosystems often ignore evolutionary changes in response to altered selective regimes. Freshwater habitats for Snake River fall Chinook salmon (SRFCS), a threatened species in the US, have been dramatically changed by hydropower development and other watershed modifications. Associated biological changes include a shift in juvenile life history: Historically essentially 100% of juveniles migrated to sea as subyearlings, but a substantial fraction have migrated as yearlings in recent years. In contemplating future management actions for this species should major Snake River dams ever be removed (as many have proposed), it will be important to understand whether evolution is at least partially responsible for this life‐history change. We hypothesized that if this trait is genetically based, parents who migrated to sea as subyearlings should produce faster‐growing offspring that would be more likely to reach a size threshold to migrate to sea in their first year. We tested this with phenotypic data for over 2,600 juvenile SRFCS that were genetically matched to parents of hatchery and natural origin. Three lines of evidence supported our hypothesis: (i) the animal model estimated substantial heritability for juvenile growth rate for three consecutive cohorts; (ii) linear modeling showed an association between juvenile life history of parents and offspring growth rate; and (iii) faster‐growing juveniles migrated at greater speeds, as expected if they were more likely to be heading to sea. Surprisingly, we also found that parents reared a full year in a hatchery produced the fastest growing offspring of all—apparently an example of cross‐generational plasticity associated with artificial propagation. We suggest that SRFCS is an example of a potentially large class of species that can be considered to be “anthro‐evolutionary”—signifying those whose evolutionary trajectories have been profoundly shaped by altered selective regimes in human‐dominated landscapes.

The sound of migration: exploring data sonification as a means of interpreting multivariate salmon movement datasets

“…The data used to create the sonifications were taken from a dataset of threatened Fall Chinook salmon in the Snake River in the northwestern United States ( Hegg et al., 2013 ). Juvenile movement timing is important to ecologists and managers because recent evidence suggests that the population may be evolving novel migration patterns in response to dams and other anthropogenic affects across their habitat ( Waples et al., 2017 ; Williams et al., 2008 ).…”

“…Understanding the timing of large numbers of salmon movements is particularly important in one population of Fall Chinook salmon in the Snake River in the northwestern United States. Recent evidence indicates that the timing of ocean migration in juveniles of this population may be evolving due to human induced changes in the river system ( Waples et al., 2017 ; Williams et al., 2008 ). Migration in these fish has changed from exclusively early outmigration in their first summer (sub-yearling) historically, to a mix of migration timings that includes fish which enter the ocean the following spring (yearling) ( Connor et al., 2005 ).…”

Salmon Genetics and Management in the Columbia River Basin

“…For example, over the past 60 years, sockeye salmon in the Columbia River have displayed a trend toward earlier upstream migration timing; with contemporary adults now migrating, on average, more than 10 days earlier than they did in the 1940s (Crozier et al 2011). Modified life history strategies have also been demonstrated for Chinook salmon in the basin (Waples et al 2017). Historically, all juvenile fall Chinook salmon in the Snake River migrated to the ocean as sub-yearlings.…”

“…This life history has become so prevalent that as many as three-quarters of returning adult females are now produced from parents with the reservoir-type, yearling life history. These changes are predicted to be "anthro-evolutionary", evolutionary trajectories that have been greatly influenced by anthropogenically driven selective regimes (Waples et al 2017).…”

Robin S. Waples—Recipient of the 2018 Molecular Ecology Prize

“…Robin has also published extensively on evaluating genetic risks and benefits of fish propagation (e.g., salmon hatcheries and marine fish aquaculture; Waples, ; Waples & Drake, ; Waples, Hindar, Karlsson, & Hard, ), on integrating genetic and demographic factors into analysis of age structure and spatial structure (Waples, Scribner, et al, ) and on monitoring genetic and demographic population structure in managed species (Milligan et al, ; Schwartz, Luikart, & Waples, ; Tallmon et al, ). Recently, he has begun to explore the evolutionary responses of natural populations to human‐altered environments (Waples et al, ) and the potential of genomics to assist conservation efforts (Hendricks et al, ; Waples & Lindley, ).…”