Adaptive Evolution of Nearctic Deepwater Fish Vision: Implications for Assessing Functional Variation for Conservation.

Intraspecific functional variation is critical for adaptation to rapidly changing environments. For visual opsins, functional variation can be characterized in vitro and often reflects a species' ecological niche but is rarely considered in the context of intraspecific variation or the impact of recent environmental changes on species of cultural or commercial significance. Investigation of adaptation in postglacial lakes can provide key insight into how rapid environmental changes impact functional evolution. Here, we report evidence for molecular adaptation in vision in 2 lineages of Nearctic fishes that are deep lake specialists: ciscoes and deepwater sculpin. We found depth-related variation in the dim-light visual pigment rhodopsin that evolved convergently in these 2 lineages. In vitro characterization of spectral sensitivity of the convergent deepwater rhodopsin alleles revealed blue-shifts compared with other more widely distributed alleles. These blue-shifted rhodopsin alleles were only observed in deep clear postglacial lakes with underwater visual environments enriched in blue light. This provides evidence of remarkably rapid and convergent visual adaptation and intraspecific functional variation in rhodopsin. Intraspecific functional variation has important implications for conservation, and these fishes are of conservation concern and great cultural, commercial, and nutritional importance to Indigenous communities. We collaborated with the Saugeen Ojibway Nation to develop and test a metabarcoding approach that we show is efficient and accurate in recovering the ecological distribution of functionally relevant variation in rhodopsin. Our approach bridges experimental analyses of protein function and genetics-based tools used in large-scale surveys to better understand the ecological extent of adaptive functional variation.

Effects-based marine ecological risk assessment at a polychlorinated biphenyl-contaminated site in Saglek, Labrador, Canada.

Although the presence and distribution of polychlorinated biphenyls (PCBs) in Arctic marine environments has been well documented, the implications for the health of biota are poorly understood. In the present study, multiple lines of evidence, including site-specific effects data, were used to assess PCB-related risks to marine biota at a contaminated military site in Saglek Bay, Labrador, Canada, from 1997 to 1999. Risks were evaluated for three components of the ecosystem: benthic invertebrates, a bottom-feeding fish (shorthorn sculpin, Myoxocephalus scorpius), and a diving seabird (black guillemot, Cepphus grylle). Average sediment PCB concentrations exceeded the Canadian interim sediment quality guideline level by 41-fold. However, sediment toxicity testing and a benthic community survey showed no evidence of adverse effects. In contrast, shorthorn sculpin and black guillemot PCB exposures (measured as sum of 55 congeners) were elevated enough to pose risks to survival or reproduction. Based on the collective evidence, the authors estimated that risks were posed by sediment PCB concentrations greater than 77 ng/g dry weight for black guillemots and 750 ng/g dry weight for shorthorn sculpins. The present study, along with two parallel studies, provided information to support the management decisions concerning potential remedial action on the contaminated sediments. This ecological risk assessment describes the steps and rationale taken to evaluate the risk posed by an area of PCB-contaminated marine sediments in an otherwise relatively pristine northern coastal environment.

Reduction of PCB contamination in an Arctic coastal environment: a first step in assessing ecosystem recovery after the removal of a point source.

Studies have documented the presence of organic contaminants in Arctic marine environments due to local point sources, but little long-term data is known of the recovery process once those contaminants are removed. In this study, natural recovery of a local marine food web from a historic terrestrial source of polychlorinated biphenyls (PCBs) at Saglek Bay is examined. PCBs were measured in marine sediments, shorthorn sculpin (Myoxocephalus scorpius), and black guillemots (Cepphus grylle) to assess ecosystem recovery over an eight-year period after cleanup of the source. Surface sediment measurements indicate decreases in both the extent and average concentrations of PCBs throughout Saglek Bay. Sculpin collected near the former contaminated beach in 2006 had significantly lower PCB burdens than those collected in 1998/ 99. PCB levels have also decreased significantly in black guillemot nestlings collected from the former contaminated beach area, as well as Island (6-8 km from the source) and Reference (greater than 18 km from the source) locations. This study demonstrates the utility of using indicator species, especially the black guillemot, to monitor PCB uptake in benthic food webs. The rapid decreases in the physical and biotic PCB concentrations from the local ecosystem at Saglek Bay demonstratethe efficiency with which natural ecosystem recovery can take place in a highly energetic coastal marine environment once a chronic contaminant source is removed.

Parasites of the deepwater sculpin (Myoxocephalus thompsonii) across its Canadian range.

Deepwater sculpin (Myoxocephalus thompsonii) were collected from 19 lakes across the species' distribution in Canada and examined for parasites. Six helminth species (Crepidostomum farionis, Bothriocephalus cuspidatus, Proteocephalus sp., Cyathocephalus truncatus, Raphidascaris acus, and Echinorhynchus salmonis), 1 crustacean species (Ergasilus nerkae), and 1 molluscan species (glochidia) parasitized these hosts. Crepidostomum farionis, Proteocephalus sp., R. acus, E. nerkae, and the glochidia represent new parasite records for this host species. Overall parasite prevalence was 78.0% while mean intensity was 6.1 +/- 7.1 SD. Bothriocephalus cuspidatus was the most prevalent parasite and was recorded from 62.2% of the deepwater sculpin and found in 17 of the 19 lakes. The low-productivity habitat of this host limits the parasites available for transmission, and the infra- and component communities were generally species poor. With the exception of the Proteocephalus sp., all of the helminth parasites recovered have been reported as adults in lake trout (Salvelinus namaycush) or burbot (Lota lota), suggesting that, in the lakes where they occur, deepwater sculpin may play an important role in energetic transfer and parasitic transmission to higher trophic levels.