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Hypersaline lakes in arid and semi-arid areas are unique ecosystems that harbour unique extremophile organisms such as Artemia , the paradigmatic example of adaptation to harsh living conditions. We assessed the mitogenomic biodiversity of Artemia species from the Tibetan Plateau, China, a remote and yet minimally disturbed ecosystem with a variety of hypersaline lakes. Analysis of ten Tibetan salt lakes demonstrated the occurrence of two regionally endemic species, Artemia tibetiana and Artemia sorgeloosi , with the latter being the dominant species with eight localities. Both species coexist in Jingyu and Jibu lakes, representing the first case of natural distribution overlap between sexual Artemia species. Artemia sorgeloosi exhibits higher genetic diversity and interpopulation differences, a result consistent with the heterogeneity of local salt lakes, local Artemia population demographics, and their adaptive potentials. Significant F ST values demonstrate a gene flow barrier between A. sorgeloosi populations that is compatible with an 'island biogeography' distribution pattern, making the Tibetan Plateau a sort of natural laboratory to study intraspecific population differences. Artemia sorgeloosi and the exotic Artemia franciscana were found coexisting in Yangnapen Lake, demonstrating the ability of this invasive species to colonize high-altitude inland habitats, and the need to monitor its presence and eventual expansion. [ABSTRACT FROM AUTHOR]

Species of Artemia are regionally endemic branchiopod crustaceans composed of sexual species and parthenogenetic lineages, and represent an excellent model for studying adaptation and speciation to extreme and heterogeneous hypersaline environments. We tested hypotheses of whether populations from the Tibetan Plateau belong to A. tibetiana Abatzopoulos, Zhang & Sorgeloos,1998 and whether a population from Kazakhstan is a new species, using other Asian species of Artemia as outgroups. We conducted a multitrait phylogenetic study based on the complete mitogenome, mitochondrial (COI, 12S, 16S) and nuclear (microsatellites, ITS1) markers, and a suit of uni- and multivariate morphological traits. Our results led to the discovery of two new species, one from the Tibetan Plateau (Haiyan Lake) in China (Artemia sorgeloosi n. sp.) and a second from Kazakhstan (Artemia amati n. sp.). Our analysis demonstrate that A. tibetiana and A. amati n. sp. are monophyletic, whereas A. sorgeloosi n. sp. , and A. tibetiana are polyphyletic. Evolutionary relationships based on mitochondrial and nSSR markers suggest that A. tibetiana may have arisen from a past hybridization event of a maternal ancestor of A. tibetiana with A. sorgeloosi n. sp. or its ancestor. We present the complete mitogenome of A. tibetiana , A. amati n. sp. , and A. sorgeloosi n. sp. We also provide a novel taxonomic identification key based on morphology, emphasizing the phenotype as a necessary component of the species concept. [ABSTRACT FROM AUTHOR]