The parasitic sea lamprey (Petromyzon marinus) has caused extensive losses to commercial fish stocks of the upper Great Lakes of North America. Methods of controlling the sea lamprey include trapping, barriers to prevent migration, and use of a chemical lampricide (3-trifluoromethyl-4-nitrophenol) to kill the filter-feeding larvae. Concerns about the non-specificity of these methods have prompted continued development of species-specific methods to control lampreys outside their native range. In this study, we considered the utility of RNA interference to develop a sea lamprey-specific lampricide. Injection of six different short interfering, double-stranded RNAs (siRNAs) into lamprey embryos first confirmed that the siRNAs could reduce the targeted transcript levels by more than 50%. Two size classes of lamprey larvae were then fed the siRNAs complexed with liposomes, and three of the siRNAs (targeting elongation factor 1α, calmodulin, and α-actinin) reduced transcript levels 2.5, 3.6, and 5.0–fold, respectively, within the lamprey midsections. This is not only the first demonstration of RNAi in lampreys, but it is also the first example of delivery of siRNAs to a non-mammalian vertebrate through feeding formulations. One of the siRNA treatments also caused increased mortality of the larvae following a single feeding of siRNAs, which suggests that prolonged or multiple feedings of siRNAs could be used to kill filter-feeding larvae within streams, following development of a slow-release formulation. The genes targeted in this study are highly conserved across many species, and only serve as a proof-of-concept demonstration that siRNAs can be used in lampreys. Given that RNA interference is a sequence-specific phenomenon, it should be possible to design siRNAs that selectively target gene sequences that are unique to sea lampreys, and thus develop a technology to control these pests without adversely affecting non-target species.

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Aquaculture in North America is currently dominated by Atlantic salmon, but there has been an increasing interest in the production of species native to the Pacific coast.Chinook salmon is relatively new to production; therefore, the selection of appropriate stocks is critical. Often genes from wild populations are incorporated into farmed stocks to avoid performance decreases associated with inbreeding. The present study focuses on assessing the immunological performance of one inbred stock and seven outbred/hybrid crosses after challenge with the marine pathogen, Vibrio anguillarum.Throughout exposure challenge to both pathogen and sterile PBS, significant differences in mortality were observed between crosses. Fish were also assessed for major histocompatibility complex (MHC) class II β1 genotype, and although particular alleles did not confer resistance, crosses with better survival had more individuals presenting a heterozygous genotype. The stress induced during infection resulted in several individuals presenting signs of Bacterial Kidney Disease (Renibacterium salmoninarum) indicating that chronic co-infection may have contributed to susceptibility. When spleen samples from the highest and lowest performing hybrid crosses were assessed for cytokine and respiratory burst gene expression throughout bacterial challenge, high surviving crosses presented lower expression of inflammatory cytokine transcripts (IL-1β, IL-6 and TNFα) when compared to low performing crosses. Interestingly, microsatellite analysis revealed no significant differences in inbreeding coefficient or allelic richness between crosses despite observed variation in immune performance.Understanding the impact of outbreeding on the immune function of farmed, and often inbred, Chinook salmon could aid in future development of high-quality aquaculture stocks for this species.

Droughts on the North American Great Plains once led to elevated levels of out‐migration from rural areas. Large‐scale drought migration has not been observed since the 1950s due to changes in land management and agricultural systems that lessened farm‐level vulnerability to drought. Have droughts had less observable population impacts in subsequent decades? Here, we present findings from an investigation of an unusually severe, localised drought that struck eastern South Dakota in 1976 and caused staggering financial losses to farms. County‐level population and net migration rates show an anomalous increase of migration into drought‐affected counties by male migrants in the age group 30–35 years, likely being return migrants coming to help on the family farm. Newspaper archives and interviews with retired farmers suggest that few people moved away during the 1976 drought; most adapted instead by selling off their livestock herds and taking on greater debt. However, a commonly expressed view is that the drought ‘softened up’ area farmers, increasing their vulnerability to interest rates that quadrupled in the three following years. The early 1980s saw high rates of farm failures, unemployment and population decline in counties that experienced the worst impacts of the 1976 drought, suggesting the drought had a lag effect on population patterns. The findings from this case study are consistent with the ‘lessening hypothesis’ that social and technological innovations reduce economic and population impacts of recurrent climatic risks but elevate vulnerability to less frequent, unusually severe events.

<p>Rural migration responses to drought are complex, context specific, and multi-directional. Migration is one of many possible adaptive responses to drought, and is typically initiated only after other, less disruptive strategies have been attempted. The potential for drought to stimulate migration or displacement is inversely related to the range of alternative adaptation options available to households, and is lowered through coordinated vulnerability-reduction mechanisms such as institutional water-management regimes and crop insurance programs. When drought-related migration does occur, it tends to flow along pre-existing social networks to known destinations, which are usually urban centres within the same state/country or in contiguous ones. Using a mixed-methods approach that combines geospatial tools, quantitative methods (i.e. random forest and spatial regression) and qualitative data gathered through archival research and local interviews, we have generated detailed models of the changing influence over time of drought on rural population patterns on the North American Great Plains. In this presentation we highlight key findings from our work, describe data needs and limitations, discuss the predictive power of various quantitative methods, identify non-climatic variables that mediate migration outcomes, and emphasize the importance of mixed-methods approaches.</p>