• Environmental, biological, and genetic factors influencing local adaptation of pink salmon (Oncorhynchus gorbuscha) in Auke Creek, Alaska

      Manhard, Christopher V.; Gharrett, Anthony J.; Smoker, William W.; Joyce, John E.; Hard, Jeffrey J.; Adkison, Milo D. (2016-05)
      Pacific salmon form distinct, locally adapted populations because of the spatial and temporal precision with which they home to their natal streams. Local adaptation is recognized as an important component underlying the productivity and sustainability of salmonid populations, yet there remains uncertainty of the scale at which it occurs. This uncertainty was addressed by analysis of demographic, genetic, and experimental data collected from seasonally structured brood lines of Pink Salmon that spawn in Auke Creek, Alaska. An extensive background of research on this system has indicated that the timing of the adult and juvenile migrations is closely aligned with fitness and productivity in this stream; this background provided a framework for synthesizing the results of the analyses to address these questions: (1) What ecological factors influence productivity of the freshwater and marine life history stages; (2) Do these factors suggest a mechanism for evolution of migration time; (3) What are the consequences of disrupting fine-scale local adaptation of migration time? Freshwater productivity appeared to be influenced primarily by competition for spawning habitat, rather than variability in environmental conditions. Marine productivity, conversely, was associated with physical processes that influence survival of juveniles in the nearshore environment. Consistent with these findings, genetic evolution of earlier migration time, which was observed in both adults and juveniles over two generations, appeared to be driven by earlier vernal warming of the nearshore environment. Despite these environmental changes and resulting selection against late migrating fish, recruitment to Auke Creek has remained stable, thereby indicating that seasonal structure of migration time has supported sustained productivity in a changing climate. Experimental relaxation of natural barriers to gene flow that maintain the seasonal structure resulted in intermediate adult migration times in two generations of hybrid fish. These patterns were consistent with an additive genetic basis for migration time and suggest that ecological outbreeding depression is a post-zygotic mechanism that maintains adaptive variation of migration time in Auke Creek. Collectively, these results provide evidence that fine-scale local adaptation can enhance productivity of salmonid populations while providing resilience to climate change.
    • A test of local adaptation in seasonally separate subpopulations of pink salmon (Oncorhynchus gorbuscha)

      Manhard, Christopher V.; Gharrett, Anthony; Smoker, William; Adkison, Milo (2012-12)
      Differences in fitness related traits were observed between first generation (F₁) hybrid and control lines of temporally distinct subpopulations of pink salmon (Oncorhynchus gorbuscha). The lines were cultured in a common freshwater environment, released to sea together, and collected at their natal stream as adults. Early-and late-run pink salmon, which are partially genetically isolated by the time at which they return to Auke Creek in Southeast Alaska to spawn, were crossed to create F₁ and F₂ hybrid groups in the even- and odd-year brood lines. Marine survival of controls exceeded that of F₁ hybrids of the even-year brood line, whereas no difference in marine survival between those experimental groups was detected in the odd-year brood line. First generation hybrids expressed intermediate time of return relative to controls in both brood lines. Second generation hybrids exhibited similar embryonic development rates to controls in both brood lines. These results demonstrate that removal of a genetic barrier as fine as that which occurs within a brood line and location can disrupt local adaptation in a population of pink salmon, which may cause outbreeding depression in hybrids and may potentially reduce the overall biodiversity and productivity of the population.