Zenker, Armin
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Large‐scale eDNA monitoring of multiple aquatic pathogens as a tool to provide risk maps for wildlife diseases
Multiple parasites and pathogens cause disease in aquatic wildlife and in aquaculture species, generating a need for monitoring and management. Conventional disease monitoring methods involve laborious, costly, and invasive capture and examination of host species, and require specialized expertise for every host and pathogen of interest. Environmental DNA could provide simultaneous occurrence data for multiple pathogens across different host taxa, valuable for using parasite diversity as, for example, a bioindicator of ecosystem disturbance. Here, we tested the potential for simultaneous detection of four wildlife pathogens in water samples from 280, mainly riverine, sites across Switzerland. We targeted the crayfish pathogen, the amphibian pathogen Batrachochytrium dendrobatidis, and the fish pathogens Saprolegnia parasitica and Tetracapsuloides bryosalmonae. The eDNA detection showed a widespread distribution of A. astaciS. parasitica T. bryosalmonae A. astaci and T. bryosalmonae were not detected in some alpine river catchments. B. dendrobatidis was detected only rarely, which was expected since the sampling did not target amphibian breeding sites. Co‐detection rates were higher in rivers than in lakes, likely reflecting the habitat preferences and distributions of the host species. We discuss the advantages and limitations of eDNA‐based pathogen monitoring and list a set of recommendations for managers. Our study illustrates how eDNA‐based techniques can monitor several pathogen species concurrently, thus facilitating more comprehensive disease monitoring schemes. Combined with metabarcoding approaches in the future, eDNA‐based sampling and detection can facilitate the incorporation of parasite and pathogen occurrence and diversity as an indicator for aquatic ecosystem health, and for revealing the hidden biodiversity and structure of parasite communities.
Using eDNA to simultaneously detect the distribution of native and invasive crayfish within an entire country
The introduction of invasive crayfish has led to a decline of many European native species of crayfish across their range. In this study, novel duplex assays for all crayfish occurring in Switzerland were developed. We aimed to identify the distribution of the seven species using a traditional trap surveillance method as well by collecting water samples to detect eDNA by species-specific quantitative real-time PCR. We reveal our overall experience in finding optimal field and laboratory techniques to discover the distribution and abundance of native and invasive species in order to enhance knowledge of early invasive species invasion and highlight important pockets of populations where native species remain, for implementation of conservation strategies. Using eDNA, important populations of native noble and white-clawed crayfish were revealed in multiple waters across various cantons. The successful identification of native and invasive crayfish species in Switzerland using eDNA can be applied to future nationwide projects. This method which has the ability to detect all species simultaneously across an entire country, will allow an improvement in freshwater crayfish conservation management.
Shedding new light on early sex determination in zebrafish
In contrast to established zebrafish gene annotations, the question of sex determination has still not been conclusively clarified for developing zebrafish, Danio rerio, larvae, 28 dpf or earlier. Recent studies indicate polygenic sex determination (PSD), with the genes being distributed throughout the genome. Early genetic markers of sex in zebrafish help unravel co-founding sex-related differences to apply to human health and environmental toxicity studies. A qPCR-based method was developed for six genes: cytochrome P450, family 17, subfamily A, polypeptide 1 (cyp17a1); cytochrome P450, family 19, subfam-ily A, polypeptide 1a (cyp19a1a); cytochrome P450, family 19, subfamily A, polypeptides 1b (cyp19a1b); vitellogenin 1 (vtg1); nuclear receptor subfamily 0, group B, member 1 (nr0b1), sry (sex-determining region Y)-box 9b (sox9b) and actin, beta 1 (actb1), the reference gene. Sry-box 9a (Sox9a), insulin-like growth factor 3 (igf3) and double sex and mab-3 related transcription factor 1 (dmrt1), which are also known to be associated with sex determination, were used in gene expression tests. Additionally, Next-Generation-Sequencing (NGS) sequenced the genome of two adult female and male and two juve-niles. PCR analysis of adult zebrafish revealed sex-specific expression of cyp17a1, cyp19a1a, vtg1, igf3 and dmrt1, the first four strongly expressed in female zebrafish and the last one highly expressed in male conspecifics. From NGS, nine female and four male-fated genes were selected as novel for assessing zebrafish sex, 28 dpf. Differences in transcriptomes allowed allocation of sex-specific genes also expressed in juvenile zebrafish
Barriers against invasive crayfish species in natural waters and fish passes. Practical experience
The spread of non-indigenous crayfish species poses a threat to local populations of crayfish as well as to other fauna and flora across Europe and around the world. Several methods have been used in attempt to reduce their numbers and stop their further spread. Crayfish barriers are the best way to stop the non-anthropogenic spread of established invasive crayfish populations. Up to now there are very few published papers regarding crayfish barrier design and practical experience in construction. For the last seven years, we have optimised construction and functionality of crayfish barriers, tested various building materials and planned construction of many barriers across Switzerland. In this article, we highlight our experience, share the acquired knowledge and present the newest findings regarding considerations, which must be made when planning a barrier to stop the upstream movement of non-indigenous crayfish species. From our experience we conclude that crayfish barriers work in preventing the movement of invasive species if certain factors are taken into account. Barrier design and construction must be specific for each project, because the size of the watercourse, flow velocity, bank conditions, existing constructions and accessibility, all change the way a barrier should be set-up.