Spatial structuring of an evolving life-history strategy under altered environmental conditions

Abstract

Human disturbances to ecosystems have created challenges to populations worldwide, forcing them to respond phenotypically in ways that increase their fitness under current conditions. One approach to examining population responses to disturbance in species with complex life histories is to study species that exhibit spatial patterns in their phenotypic response across populations or demes. In this study, we investigate a threatened population of fall chinook salmon (Oncorhynchus tshawytscha) in the Snake River of Idaho, in which a significant fraction of the juvenile population have been shown to exhibit a yearling out-migration strategy which had not previously been thought to exist. It has been suggested that dam-related environmental changes may have altered the selective pressures experienced by out-migrating fall chinook, driving evolution of a later and more selectively advantageous migration strategy. Using isotopic analysis of otoliths from returning adult spawners, we reconstructed the locations of individual fish at three major juvenile life stages to determine if the representation of the yearling life history was geographically structured within the population. We reconstructed juvenile locations for natal, rearing and overwintering life stages in each of the major spawning areas in the basin. Our results indicate that the yearling life-history strategy is predominantly represented within one of the main spawning regions, the Clearwater River, rather than being distributed throughout the basin. Previous studies have shown the Clearwater River to have cooler temperatures, later hatch dates, and later outmigration of juveniles, indicating a link between environment and expression of the yearling life history. Our data suggest that this new yearling life history may be disproportionally represented in returning adult spawners, indicating selection for this life history within the population.

Movement patterns and dispersal potential of Pecos bluntnose shiner (Notropis simus pecosensis) revealed using otolith microchemistry

“…These formations consist of carbonate (limestone and dolomite) and evaporite (gypsum and halite). Thus, older bedrock in the northern portion of the river is reflected by higher 87 Sr: 86 Sr values, while younger bedrock in the southern portion of the river is reflected by lower 87 Sr: 86 Sr values (Barnett-Johnson et al 2008;Hegg et al 2013).…”

Using otolith chemical and structural analysis to investigate reservoir habitat use by juvenile Chinook salmon Oncorhynchus tshawytscha

“…Elemental concentrations of Ca, Sr, Ba, Mg and Mn were analysed with an inductively‐coupled plasma mass spectrometer (ICP‐MS – Finnigan‐Thermo Element II) using analytical methods and instrument conditions described in Hegg et al . ().…”

“…Oncorhynchus tshawytscha exhibit a diverse array of movements, both in terms of dispersal behaviours and migration, which collectively contribute to variability in juvenile freshwater habitat use within populations (Quinn, ; Hamann & Kennedy, ; Hegg et al ., ). Anthropogenic alterations (particularly dams and associated reservoirs) affect habitat use among individuals (Williams et al ., ), and life‐history plasticity is hypothesized to provide resilience to anthropogenic as well as natural perturbations (Waples et al ., ).…”

Validation of Daily Increment Formation in Otoliths from Spring Chinook Salmon

“…Volk et al (2010), on the other hand, conducted a mark-recapture study to investigate the periodicity of otolith increment formation. For our study, confirmation of an emergence check and of daily increment formation grew out of our need to better understand early life history development (Zabel and Achord 2004), growth (Achord et al 2007, Zabel et al 2010, and habitat use (Hegg et al 2013) so as to predict survival to adulthood Williams 2002, Miller et al 2010). Further, we sought to contribute to literature regarding increment validation of Chinook salmon by focusing on the Yakima River population in Washington State, compared to work of Volk et al (2010), which used fish from Salmon River in Oregon, and Neilson and Geen (1982) and Gauldie (1991), which used Chinook salmon from Vancouver, British Columbia, Canada.…”