Swedish populations of Wels catfish (Silurus glanis) experienced severe declines during the 19th and 20th centuries. The main causes for the decline were loss of suitable spawning habitat and fragmentation of populations. Currently, three native and two reintroduced populations remain in Sweden. Thanks to national protection and progress in restoring habitats, population sizes have increased over the past three decades. Previous studies that used microsatellite loci have found that genetic diversity and effective population sizes in Sweden are low, while population differentiation is high. A study that used whole genome sequencing (WGS) confirmed these results for native Swedish populations (those found in the Båven, Emån, and Möckeln water systems). The current project uses the same WGS methods and expands on the previous study by considering samples from non-Swedish populations (river Garonne, France; river Ebro, Spain; hatchery, Czech Republic), as well as improving read-depth coverage and sampling from the introduced Swedish population in the Helge å water system. Both a genome-wide SNP-set and full mitochondrial sequences were used to assess genetic diversity within each population, and differentiation among them. Genetic diversity in Swedish populations is lower than in non-Swedish populations. Native Swedish populations are strongly differentiated from one another. The introduced Helge å population is strongly differentiated from Emån and Möckeln, but less so from Båven. Despite Helge å individuals having heritage that can be predominantly traced to Båven, there are clear signs of admixture with the other two native populations. Swedish populations are all strongly differentiated from the non-Swedish populations. Altogether, evidence of admixture and slightly greater genetic diversity than native Swedish populations in Helge å can at the surface be seen as promising signs. However, it remains uncertain whether these improvements are durable over multiple generations. Considering the poor genetic status of Sweden taken as a whole, and the questionable nature of the improvements seen in Helge å, the long-term viability of Swedish catfish populations remains uncertain.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-488414 |
| Date | January 2022 |
| Creators | Littmann, Lars |
| Publisher | Uppsala universitet, Institutionen för ekologi och genetik, Uppsala universitet, Institutionen för biologisk grundutbildning |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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