Genetic effects of habitat restoration in the Laurentian Great Lakes: an assessment of lake sturgeon origin and genetic diversity

Effect of water temperature on frog virus 3 disease in hatchery-reared pallid sturgeon Scaphirhynchus albus

Ranaviruses are large double-stranded DNA viruses within the genus Ranavirus (family Iridoviridae) that are being detected with increasing frequency among aquacultured and wild fishes. In the USA, multiple sturgeon hatcheries have experienced ranavirus epizootics resulting in significant morbidity and mortality in young-of-year (YOY). Significant economic losses have resulted from repeated outbreaks of frog virus 3 (FV3), the type species for the genus Ranavirus, in YOY pallid sturgeon Scaphirhynchus albus reared at a hatchery within the Missouri River Basin. Water temperature and stocking density are known to influence the severity of ranavirus disease in ectothermic vertebrates. To determine the effect of water temperature on ranavirus disease in hatchery-raised S. albus, we conducted FV3 challenges at 2 temperatures (17 and 23°C) and compared cumulative survival over a 28 d study period. A mean (±SE) survival rate of 57.5 ± 13.2% was observed in replicate tanks of sturgeon maintained at 23°C, whereas no mortality was observed among sturgeon maintained at 17°C. In a second challenge study, we compared the effect of water temperature on disease progression by regularly sampling fish over the study period and evaluating lesions by histopathology and in situ hybridization, and by assessing viral titer and load in external and internal tissues using virus isolation and qPCR, respectively. Results suggest that temperature manipulation may be an effective mitigation strategy that sturgeon hatcheries can employ to minimize ranavirus-associated disease.

Variation in DNA methylation is associated with migratory phenotypes of lake sturgeon Acipenser fulvescens in the St. Clair River, MI, USA

Lake sturgeon Acipenser fulvescens populations show a variety of movement patterns that are poorly understood. To compare two migratory phenotypes of A. fulvescens in the St. Clair River, MI, USA, multiple data types were analysed. Individual fish were classified into migratory phenotypes based on acoustic telemetry data collected 2012-2015. Acipenser fulvescens consistently showed movement from the St. Clair River upriver into Lake Huron or downriver into Lake St. Clair. The two migratory phenotypes were then compared for differences in morphometrics, genetics and epigenetics. Morphological differences based on linear measurements were not detected between phenotypes. Microsatellite data from 11 loci suggested one population with no genetic differentiation between migratory phenotypes. Our epigenetic results indicated that the migratory phenotypes are differentially methylated (P < 0.05), thus epigenetics may be associated with migratory differences in A. fulvescens. Only one restriction site was identified to be driving the differential methylation (P < 0.05). While little evidence at neutral loci occurred for genetic differentiation of A. fulvescens, DNA methylation may play a role in the observed movement pattern variation. When combined with microsatellite and morphometric analyses, our results suggested that different migratory patterns may reflect phenotypic plasticity, allowing A. fulvescens to acclimate to short-term environmental variability. Without an integrated approach, the role of epigenetics in the migratory phenotype of A. fulvescens may have been overlooked. Further characterization of migratory phenotypes could be important for management to conserve behavioural variation across the distribution of A. fulvescens and for design of stocking guidelines.

Direct and indirect effects of different types of microplastics on freshwater prey (Corbicula fluminea) and their predator (Acipenser transmontanus)

We examined whether environmentally relevant concentrations of different types of microplastics, with or without PCBs, directly affect freshwater prey and indirectly affect their predators. Asian clams (Corbicula fluminea) were exposed to environmentally relevant concentrations of polyethylene terephthalate (PET), polyethylene, polyvinylchloride (PVC) or polystyrene with and without polychlorinated biphenyls (PCBs) for 28 days. Their predators, white sturgeon (Acipenser transmontanus), were exposed to clams from each treatment for 28 days. In both species, we examined bioaccumulation of PCBs and effects (i.e., immunohistochemistry, histology, behavior, condition, mortality) across several levels of biological organization. PCBs were not detected in prey or predator, and thus differences in bioaccumulation of PCBs among polymers and biomagnification in predators could not be measured. One of the main objectives of this study was to test the hypothesis that bioaccumulation of PCBs would differ among polymer types. Because we could not answer this question experimentally, a bioaccumulation model was run and predicted that concentrations of PCBs in clams exposed to polyethylene and polystyrene would be greater than PET and PVC. Observed effects, although subtle, seemed to be due to microplastics rather than PCBs alone. For example, histopathology showed tubular dilation in clams exposed to microplastics with PCBs, with only mild effects in clams exposed to PCBs alone.