Conservation genetics and management implications for European grayling, Thymallus thymallus: synthesis of phylogeography and population genetics

Abstract

European grayling, Thymallus thymallus (L.), populations have steadily declined since the mid-1980s, mostly because of habitat degradation and increased predation pressure. To provide guidelines for conservation strategies and future management programmes, delineation of conservation and management units is warranted. Over the last decade, several studies have investigated the phylogeography and population genetic structure of T. thymallus using mitochondrial and nuclear microsatellite DNA markers. However, no study has covered the distribution range of T. thymallus across Europe; thus, a comprehensive survey of the evolutionary history of the species is lacking. This paper synthesises the major findings of the molecular studies and provides guidelines for the conservation and management of genetic resources of T. thymallus. At least five major mtDNA lineages have evolved in geographical isolation during the Pleistocene and these lineages should be recognised as the basic evolutionary significant units for T. thymallus in northern, central and southern Europe. There is also evidence for a high level of admixture among major lineages and sublineages, especially in the contact zones of drainages (e.g. in mainland Sweden and Norway and in central Germany), most probably resulting from a complex process of post-glacial and inter-glacial colonisation and re-colonisation events from different refugia during the Pleistocene ice ages. Based on the microsatellite data, T. thymallus shows a substantial level of inter-population genetic differentiation and, compared with other freshwater fish species, a relatively low level of within-population genetic diversity. The species develops discrete population structure, both within hydrologically connected rivers or lakes on comparatively small scales as well as in large river systems. K E Y W O R D S : evolutionary significant units, genetic diversity, microsatellites, mtDNA, salmonids.

Drainage-independent genetic structure and high genetic diversity of endangered freshwater pearl mussels (Margaritifera margaritifera) in northern Europe

“…This pattern is also reflected in the probability of common ancestors (2MOD), which was much contact zone where distinct evolutionary lineages have met in diverse taxonomic groups, resulting in an overall increased genetic diversity (Taberlet et al 1998;Hewitt 2000). These patterns have also been observed in aquatic species such as grayling (Thymallus thymallus; Gum et al 2009), a fish which frequently co-occurs with freshwater pearl mussels (Geist et al 2006). The validity of the contact zone in pearl mussel could explain the high genetic diversity found in this area.…”

“…A geographical zone in central Sweden has been described as a major European contact zone for genetically divergent evolutionary lineages in many species (reviewed in Taberlet et al 1998;Hewitt 2000), including aquatic taxa and fish species (e.g. Gum et al 2009). This region was thus selected as a candidate area for studying the genetic structuring of pearl mussels and for comparing it with results on the genetic variation within and between populations from central, southern and northeastern Europe.…”

Historical and recent genetic bottlenecks in European grayling, Thymallus thymallus

“…This divergence clearly predates the late Pleistocene period (130,000-10,000 years) implying that European grayling survived dramatic temperature oscillations in distinct refugia (see review in Gum et al 2009). Our study included 34 populations originating from the three lineages and the coalescent analyses using an hierarchical Bayesian model suggested that all grayling populations have experienced dramatic size reductions that date back 1,000-10,000 or 32,000-100,000 years, depending whether an exponential or linear population growth/decline model was used.…”

Substantial genetic structure among stocked and native populations of the European grayling (Thymallus thymallus, Salmonidae) in the United Kingdom

“…European grayling (Thymallus thymallus) are widely distributed over Northern Europe and Russia, extending from Wales in the West to the Ural mountains in the East and have undergone significant declines in numbers in many populations due to environmental degradation and overexploitation (Gum et al 2009). Conservation assessments made during the 1980s concluded that the species was endangered in the UK and threatened within Europe (Lelek 1984) and in an effort to conserve the species, stocking has been implemented in a number of European countries (Ibbotson et al 2001;Sušnik et al 2004;Gum et al 2006).…”

“…However, continuing habitat degradation and over-fishing at the local scale mean that the active conservation of grayling remains of pressing importance in Europe (e.g. Meldgaard et al 2003;Bergerot et al 2008;Gum et al 2009). …”