Few studies have determined whether formal estimates of selection explain patterns of trait divergence among populations, yet this is one approach for evaluating whether the populations are in ...equilibria. If adaptive divergence is complete, directional selection should be absent and stabilizing selection should prevail. We estimated natural selection, due to bear predation, acting on the body size and shape of male salmon in three breeding populations that experience differing predation regimes. Our approach was to (1) estimate selection acting within each population on each trait based on an empirical estimate of reproductive activity, (2) test for trait divergence among populations, and (3) test whether selection coefficients were correlated with trait divergence among populations. Stabilizing selection was never significant, indicating that these populations have yet to attain equilibria. Directional selection varied among populations in a manner consistent with trait divergence, indicating ongoing population differentiation. Specifically, the rank order of the creeks in terms of patterns of selection paralleled the rank order in terms of size and shape. The shortest and least deep-bodied males had the highest reproductive activity in the creek with the most intense predation and longer and deeper-bodied males were favored in the creeks with lower predation risk.
Conservation hatcheries are becoming a tool in rebuilding salmonid populations, but their contributions are strongly debated. Most studies focus on genetic, morphological, and behavioural, issues and ...less is known of the importance of infectious agents. The Living Gene Bank (LGB) program of the British Columbia Ministry of the Environment is a recent effort to restore collapsed steelhead trout (Oncorhynchus mykiss) populations on the east coast of Vancouver Island. Our study describes the change in macro- and microparasitic profiles of LGB-hatchery-produced juveniles after they leave the hatchery and enter the natural river environment and also compares them with a limited wild smolt sample. We found that the hatchery was successful in raising parr free of infectious agents, but once introduced into the river environment, the hatchery fish quickly took on a diverse profile of infectious agents. The high numbers of fish released from the hatchery and the existence of hatchery fish that stay in the river as residents increased the number of fish in the system with sub-clinical levels of infection. An ecological understanding of the role resident hatchery fish play in the spatial distribution of infectious agents as well as the temporal and seasonal variations in infectious agent prevalence and diversity will be important in determining the net effect of the LGB conservation hatchery on the wild population. Nomenclature: Behnke, 1992.
Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum, is a slowly progressing disease that threatens salmon conservation and restoration programs in North America. The purpose of this ...study was to track naturally occurring R. salmoninarum infection in representative, Michigan, USA, salmonid stocks using nested polymerase chain reaction (nPCR), quantitative enzyme-linked immunosorbent assay (Q-ELISA), and culture. The Q-ELISA test detected 67.6% infection prevalence, which is lower than culture (77.2%) or nPCR (94.2%), yet it provided semiquantitative data on infection intensity. The disagreement in results among the three assays may reflect the different phases of R. salmoninarum infection at the time of sampling. The testing results demonstrated the presence of six patterns, with each of the patterns representing a probable stage along the course of natural R. salmoninarum infection. Findings also suggest that fish stocks tested in this study were not uniform in the distribution of the diagnostic patterns and that, from studying such patterns, one can determine the course of BKD infection in a particular population.
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