Responses of vulnerable fishes to environmental stressors in the Canadian Great Lakes basin

Quantifying the responses of rare vulnerable species to environmental stressors poses special challenges. This study aimed to understand the responses of vulnerable fishes listed under the Species at Risk Act to environmental stressors in lakes, streams, and wetlands of the Canadian Great Lakes basin. We used a joint species distribution model (JSDM) to improve the estimates of responses of vulnerable species to environmental stressors, and the effects of functional traits on those responses, by ‟borrowing information” from abundant species having higher information content. We measured abundance, functional traits, and taxonomic relationships for 115 freshwater fish species, including 12 vulnerable species, and environmental features, at 1972 sites. The JSDM yielded more precise estimates of responses than single-species models fitted to each vulnerable species. Habitat associations inferred from the JSDM showed substantial overlap with those provided in COSEWIC status reports. Model-derived responses to environmental stressors can provide a management-friendly basis for species classification in terms of species’ tolerances to various forms of environmental change, and supplement the qualitative criteria for habitat requirements currently used in assessments of species vulnerability.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

A fine‐scale analysis reveals microgeographic hotspots maximizing infection rate between a parasite and its fish host

International audienceFor parasites, finding their hosts in vast and heterogeneous environments is a task that can be complex. Some parasite species rely on elaborate strategies to increase encounter rate with their hosts (e.g. behavioural modification of host), but others do not. For these parasites, a key issue is to reveal the processes that enable them to successfully find their hosts and complete their life cycles. Here, we tested the hypothesis that infective larvae of the freshwater ectoparasite Tracheliastes polycolpus are not homogeneously distributed along the river and preferentially occur in very specific microhabitats that maximize encounter rate, and hence infection rate, with their host fish. To do this, we combined an in situ experiment (caging) with an empirical survey carried out on the same sites to identify potential 'hotspots' of infection at the microgeographic scale and their environmental characteristics. Experimental and empirical results demonstrated that infections were not evenly distributed among microhabitats, and that infections were spatially aggregated in hotspots at a very fine spatial grain. We further found that certain combinations of environmental variables were consistently and nonlinearly associated with higher infection rate for both caged and wild-caught fish. Microhabitats characterized by very low or high stream velocities, associated with medium or very small substrate, respectively, and a deep water column were strongly and repeatedly associated with higher infection rates. These microhabitats could concentrate parasites and/or promote physical contact with the hosts. We conclude that the characteristics of some microhabitats could facilitate contact between hosts and parasites and explain how some parasites manage to find their hosts in complex environments

Development of a large SNPs resource and a low-density SNP array for brown trout (Salmo trutta) population genetics

International audienceBackground: The brown trout (Salmo trutta) is an economically and ecologically important species for which population genetic monitoring is frequently performed. The most commonly used genetic markers for this species are microsatellites and mitochondrial markers that lack replicability among laboratories, and a large genome coverage. An alternative that may be particularly efficient and universal is the development of small to large panels of Single Nucleotide Polymorphism markers (SNPs). Here, we used Restriction site Associated DNA sequences (RADs) markers to identify a set of 12,204 informative SNPs positioned on the brown trout linkage map and suitable for population genetics studies. Then, we used this novel resource to develop a cost-effective array of 192 SNPs (96 × 2) evenly spread on this map. This array was tested for genotyping success in five independent rivers occupied by two main brown trout evolutionary lineages (Atlantic-AT-and Mediterranean-ME-) on a total of 1862 individuals. Moreover, inference of admixture rate with domestic strains and population differentiation were assessed for a small river system (the Taurion River, 190 individuals) and results were compared to a panel of 13 microsatellites. Results: A high genotyping success was observed for all rivers (< 1% of non-genotyped loci per individual), although some initially used SNP failed to be amplified, probably because of mutations in primers, and were replaced. These SNPs permitted to identify patterns of isolation-by-distance for some rivers. Finally, we found that microsatellite and SNP markers yielded very similar patterns for population differentiation and admixture assessments, with SNPs having better ability to detect introgression and differentiation