Mitogenome Phylogeny of Thymallus (graylings) - Species delineation

The genus Thymallus (grayling) is distributed over much of central and northern Europe, Asia and North America in generally cold lacustrine and riverine environments. Like all salmonid fishes, grayling have a tetraploid ancestry, which attracts research interest on the ongoing process of re-diploidiazation and its potential effects on lineage diversification. Grayling are also of increasing conservation concern, especially in Europe, as their habitats are the target of multiple anthropogenic pressures. Although in the past 15 years the recognized species diversity within the genus has increased, the genetic relationships among these species remain to a degree unexplored. The last comprehensive phylogeny of Thymallus was published prior the recognition of several new species and relies only on two mtDNA genes. At present, up to 18 species have been listed. Here we inferred the phylogeny of the genus Thymallus using complete newly sequenced mitogenomes, generated through NGS and non NGS-based techniques, as well as published sources. Using this mitogenome phylogeny as well as all available mtDNA sequences for several common genes, we applied several different species delineation methods to gain some insight into the genetic support for the current species spectrum. We combine these results with a brief overview of the systematic and taxonomic status of each species or lineage, and review as well what is known concerning their range and phenotypic variability. The results serve as an initial step in reviewing the taxonomy of the entire genus and will help point out the knowledge deficits that must be eliminated before a comprehensive picture of the grayling diversity throughout the world can be achieved.