Thymallus aeliani

Taylor Elsa Froufe, Steven J. Weiss Duarte V. Gonçalves Giulia Secci-Petretto Gernot K. Englmaier André Gomes-Dos-Santos Gael P. J. Denys Henri Persat Alexander Antonov Christoph Hahn Eric B., 2021, Global systematic diversity, range distributions, conservation and taxonomic assessments of graylings (Teleostei: Salmonidae; Thymallus spp.), Organisms Diversity & Evolution (New York, N. Y.) 21 (1), pp. 25-42 : 36

Thymallus aeliani —Adriatic grayling

Occupies the middle to upper reaches of the Soca River in Slovenia and tributaries of the Po and Adige rivers in Italy ( Fig. 1 ). Divergent from T. thymallus (2.7%) and T. ligericus (3.6%) within the clade of European grayling taxa (Fig. 2). Meraner et al. (2014) reported significant regional structure in the Adige River drainage.

Taxonomic validity

A species based on its deep divergence to all other grayling and allopatric distribution in Adriatic draining rivers.

Conservation remarks

River engineering measures, hydropower expansion and water pollution are among widespread threats that have reduced at least 50% of the species range; introgression with non-native lineages is a major threat to T. aeliani and there are few pure genetic populations left ( Sušnik et al. 2004; Meraner et al. 2014). The area of aquatic occupancy may be as little as 100 sq. km. Suggested global status: Endangered.

Thymallus thymallus —European grayling

Widely distributed ( Fig. 1 ); until recently included all European stocks of grayling. They, along with T. aeliani and T. ligericus , are the only Thymallus species with a subterminal mouth. Significant phylogeographic structure throughout Western Europe ( Weiss et al. 2002; Gum et al. 2009), and from the western Balkans and Caspian Sea catchment ( Marić et al. 2012, 2014). The taxon is paraphyletic due to the systematic relationship to both T. ligericus and its sister clade of upper Danubian haplotypes.

Taxonomic validity

A species distinguished from all Asian grayling by a subterminal mouth and strict long-time allopatry to T. ligericus and T. aeliani .

Conservation remarks

Currently listed as a species of Least concern. Locally, and especially in the southern portions of its range, population declines or extinctions are widespread (see Weiss et al. 2013), leading to several endangered assignments at national levels. Suggested Global Status: Least Concern.

Thymallus ligericus — Loire grayling

Recently described endemic of the upper Loire River drainage in France ( Persat et al. 2019) ( Fig. 1 ). Populations remain genetically pure despite 50 years of stocking with foreign strains ( Persat et al. 2016), suggesting they either outcompete foreign lineages (i.e. T. thymallus ) or display reproductive isolation. Morphologically distinguished from T. thymallus by a more pointed snout, more inferior mouth and profuse spotting ( Persat et al. 2019). In our analysis, they appear as a shallow, monophyletic clade, 1.5% divergent from T. thymallus haplotypes from the upper Danube drainage and 2.2% divergent from all T. thymallus samples. The zoogeographic origins of this species in the Loire basin are unknown.

Taxonomic validity

A species based on its morphological and genetic distinction and long-term isolation (2 MY or more) from grayling of adjacent river drainages (Rhine and Rhône) ( Persat et al. 2016).

Conservation remarks

Populations are in decline and there are concerns of decreasing water flows and rising water temperatures. Its area of occupancy may not exceed 35 sq. km, but at least six or more fragmented populations exist. Suggested Global Status: Vulnerable.

Figures

Fig. 1 Map showing the global distribution range of Thymallus species. Information on sampling sites and species is given in Table S1. Numbers in the map refer to known contact zones of the following species: 1 = T. arcticus s.l. and T. baicalensis in the lower Enisei River; 2 = T. arcticus s.l. and T. baicalolenensis in the lower Lena River; 3 = T. nikolskyi and T. baicalensis in tributaries of the upper Ob River; 4 = T. baicalolenensis and T. baicalensis in tributaries of Lake Baikal; 5 = T. grubii, T. tugarinae