1. ¹Integrative Ecology Unit, Department of Ecology and Systematics, PO Box 17, 00014 University of Helsinki, Helsinki, Finland
2. ²Department of Aquaculture, Swedish University of Agricultural Sciences, Umeå, Sweden
3. ³Institute of Biology, Karelian Research Centre, Russian Academy of Sciences, Petrozavodsk, Russia
4. ⁴Polar Research Institute of Marine Fisheries and Oceanography (PINRO), Murmansk, Russia

Correspondence: M T Koskinen, Integrative Ecology Unit, Department of Ecology and Systematics, PO Box 17, 00014 University of Helsinki, Helsinki, Finland. E-mail: mtkoskin@cc.helsinki.fi.

Received 22 October 2001; Accepted 15 January 2002.

Abstract

The phylogeography of an endangered salmonid, European grayling (Thymallus thymallus), was studied based on analysis of 17 nuclear microsatellite DNA loci. In agreement with earlier mitochondrial DNA (mtDNA) studies, phylogenetic relationships of the populations suggested that northern Europe was colonized from two distinct Pleistocene refugia. Furthermore, microsatellites revealed highly supported grouping of mainland Swedish, Norwegian, Danish, German and Slovenian populations, suggesting that grayling from the northwestern and central Europe have descended from their southern conspecifics. The level of divergence between populations was substantial, even across short geographical distances. Although this was in part due to postglacial colonization patterns and contemporary barriers for gene flow, the high divergence estimates between hydrologically connected sampling locations implied efficient interpopulation reproductive isolation. Microsatellites revealed that the populations exhibited, on average, only 3.5 (2.2) alleles per locus, indicating that T. thymallus has strikingly low levels of intrapopulation genetic diversity as compared with other freshwater fish species. Accordingly, as indicated by analysis of molecular variance (AMOVA), only 49.1–58.0% of the total grayling microsatellite diversity resided within populations. A latitudinal genetic diversity gradient, potentially resulting from glaciation-mediated founder events, was not evident. Alternatively, it is possible that grayling display limited dispersal behaviour/capability, leading to low long-term effective population sizes and, consequently, depauperate intrapopulation polymorphism. These findings have implications for conservation of T. thymallus. Importantly, they exemplify that microsatellites can be highly informative for intraspecific phylogeography studies dealing with substantial divergence scales.