No abstract

The spatial spread of genetic material is fundamental to analyses of invasive species, species dispersal, and disease surveillance. Using a quantitative environmental DNA methodology, we assessed spatial variation in Atlantic salmon eDNA concentration, originating from four active salmon farms, along ~ 55 km of narrow channels in British Columbia, Canada. We evaluated eDNA from 36 and 47 seawater samples collected at 2 m and 8 m depths, respectively, at 0.3-3 km intervals along the channels. We fitted a Laplace dispersal kernel to eDNA data separately for 2 m and 8 m depths. The model estimates that 95% of eDNA spread at 2 m depth was within 1.6 km upstream and 3.2 km downstream from farms relative to a prevailing current and this was expanded at 8m (1.8 km; 3.7 km). Our results provide a benchmark for the spatial spread of biological material such as pathogens or eDNA from invasive or imperilled species in a coastal marine context. This work has implications for the interpretation of eDNA data for species surveillance and predicting disease spread.

No abstract

Ecological communities are partly structured by indirect interactions, where one species can indirectly affect another by altering its interactions with a third species. In the absence of direct predation, nonconsumptive effects of predators on prey have important implications for subsequent community interactions. To better understand these interactions, we used a Daphnia‐parasite‐predator cue system to evaluate if predation risk affects Daphnia responses to a parasite. We investigated the effects of predator cues on two aspects of host–parasite interactions (susceptibility to infection and infection intensity), and whether or not these effects differed between sexes. Our results show that changes in response to predator cues caused an increase in the prevalence and intensity of parasite infections in female predator‐exposed Daphnia. Importantly, the magnitude of infection risk depended on how long Daphnia were exposed to the cues. Additionally, heavily infected Daphnia that were constantly exposed to cues produced relatively more offspring. While males were ~5× less likely to become infected compared to females, we were unable to detect effects of predator cues on male Daphnia–parasite interactions. In sum, predators, prey, and their parasites can form complex subnetworks in food webs, necessitating a nuanced understanding of how nonconsumptive effects may mediate these interactions.

This study empirically quantifies dynamics of SARS-CoV-2 establishment and early spread in Canada. We developed a transmission model that was simulation tested and fitted in a Bayesian framework to timeseries of new cases per day prior to physical distancing interventions. A hierarchical version was fitted to all provinces simultaneously to obtain average estimates for Canada. Across scenarios of a latent period of 2–4 d and an infectious period of 5–9 d, the R0 estimate for Canada ranges from a minimum of 3.0 (95% CI: 2.3–3.9) to a maximum of 5.3 (95% CI: 3.9–7.1). Among provinces, the estimated commencement of community transmission ranged from 3 d before to 50 d after the first reported case and from 2 to 25 d before the first reports of community transmission. Among parameter scenarios and provinces, the median reduction in transmission needed to obtain R0 < 1 ranged from 46% (95% CI: 43%–48%) to 89% (95% CI: 88%–90%). Our results indicate that local epidemics of SARS-CoV-2 in Canada entail high levels of stochasticity, contagiousness, and observation delay, which facilitates rapid undetected spread and requires comprehensive testing and contact tracing for its containment.