Fish conservation in the land of steppe and sky: Evolutionarily significant units of threatened salmonid species in Mongolia mirror major river basins

Abstract

Mongolia's salmonids are suffering extensive population declines; thus, more comprehensive fisheries management and conservation strategies are required. To assist with their development, a better understanding of the genetic structure and diversity of these threatened species would allow a more targeted approach for preserving genetic variation and ultimately improve long‐term species recoveries. It is hypothesized that the unfragmented river basins that have persisted across Mongolia provide unobstructed connectivity for resident salmonid species. Thus, genetic structure is expected to be primarily segregated between major river basins. We tested this hypothesis by investigating the population structure for three salmonid genera (Hucho, Brachymystax and Thymallus) using different genetic markers to identify evolutionarily significant units (ESUs) and priority rivers to focus conservation efforts. Fish were assigned to separate ESUs when the combined evidence of mitochondrial and nuclear data indicated genetic isolation. Hucho taimen exhibited a dichotomous population structure forming two ESUs, with five priority rivers. Within the Brachymystax genus, there were three B. lenokESUs and one B. tumensisESU, along with six priority rivers. While B. tumensiswas confirmed to display divergent mtDNA haplotypes, haplotype sharing between these two congeneric species was also identified. For T. baicalensis,only a single ESU was assigned, with five priority rivers identified plus Lake Hovsgol. Additionally, we confirmed that T. nigrescens from Lake Hovsgol is a synonym of T. baicalensis. Across all species, the most prominent pattern was strong differentiation among major river basins with low differentiation and weak patterns of isolation by distance within river basins, which corroborated our hypothesis of high within‐basin connectivity across Mongolia. This new genetic information provides authorities the opportunity to distribute resources for management between ESUs while assigning additional protection for the more genetically valuable salmonid rivers so that the greatest adaptive potential within each species can be preserved.

Global systematic diversity, range distributions, conservation and taxonomic assessments of graylings (Teleostei: Salmonidae; Thymallus spp.)

“…Microsatellites and single mtDNA sequences allow no distinction between T. nigrescens and T. baicalensis (Koskinen et al 2002;Kaus et al 2019). Next-generation sequencing RAD data supported a 15-30 thousand year divergence between the two taxa (Roman et al 2018).…”

“…2). Traditional genetic markers (microsatellites and single mtDNA sequences) allow no distinction between T. nigrescens and T. baicalensis (Koskinen et al 2002;Kaus et al 2019).…”

Building a bridge between adaptive capacity and adaptive potential to understand responses to environmental change

“…Modeling approaches included systems modeling and dispersal kernels (Bonte & Bafort, 2019;Summers et al, 2012). Gene flow estimates are well established in the literature for understanding connectivity, and were measured through landscape genetics approaches, which have been applied to other conservation questions, such as restoration (Kaus et al, 2019;Manel et al, 2003;Proft et al, 2018). Importantly, connectivity estimates are beholden to the assumptions of the genetic markers used and examples exist where neutral markers may show no population structure, but traits show clear local adaptation (Fjellheim et al, 2015).…”

Building the Climate Change Resilience of Mongolia’s Blue Pearl:

“…Khuvsgul Lake supports communities of unique aquatic invertebrates (Safronov 2006;Sitnikova, Goulden, and Robinson 2006) and 10 species of fish (Free, Jensen, and Mendsaikhan 2016). One fish species, the Khuvsgul grayling, is unique to the lake and the population of another (the lenok, Brachymystax lenok) is biologically distinct, rendering the lake of global importance for this population (Kaus et al 2019). The KLNP also supports populations of at least two amphibian species ranked as vulnerable in Mongolia, the Siberian salamander (Salamandrella keyserlingii) and the Japanese tree frog (Hyla japonica) (Terbish et al 2007), which may occur in shallow wetlands and streams around Khuvsgul Lake.…”