Brine Shrimp Diversity in China Based on DNA Barcoding

Abstract

Consequently, our results on DNA barcoding and comparative analysis reveal the current distribution of Artemia species in China and phylogenetic relationship among them, providing insights into the adaptive evolution of DNA sequences of Artemia. Based on phylogenetic and divergence analyses of the selected samples from different regions of the world, it is possible that the high altitude group of Artemia are descendents of a local ancestral species in the Himalayas which diverged genetically as the Tibetan Plateau arose stepwise over approximately the last three million years (Tapponnier et al. 2001). The comparative studies among different Artemia species reveal complex sequence diversities that are expected to have functional relevance, such as energy metabolism and environmental adaptation. The highest number of adaptive variations in ATP8 implies that it is under selective pressure during long-term geographical isolation when A. tibetiana separated from their common ancestor together with the rise of Himalaya Mountains. It was reported that the ATP8 gene encodes a core subunit of F0 in ATPase that synthesizes ATP based on a protongradient that results from H+ pumping into the intermembrane space (da Fonseca, Johnson et al. 2008). It was also suggested that ATP8 may play regulatory roles in ATP synthesis among different species since it has highly variable sites in the protein-coding sequence (da Fonseca, Johnson et al. 2008). Moreover, the Ka/Ks ratio in ATP6 is also relatively high when we compared the 13 protein-coding mitochondrial genes of A. tibetiana to those of A. urmiana and A.sinica. It is known that ATP6 plays an important role in the assembly of F0 (Hadikusumo, Meltzer et al. 1988) and the highly variable sites are found in the predicted loop regions where the sequences are less selected in terms of its overall function. The high variation rates found among the ATPase subunits imply a strong selective pressure on the Artemia energy metabolism system from the high plateau environment. ： DNA barcoding is a powerful approach for characterizing species of organisms,especially those with almost identical morphological features, thereby helping to to establish phylogenetic relationships and reveal evolutionary histories. In this study, we chose a 648-bp segment of the mitochondrial gene, cytochrome c oxidase subunit 1 (COI), as a standard barcode region to establish phylogenetic relationships among brine shrimp (Artemia) species from major habitats around the world and further focused on the biodiversity of Artemia species in China, especially in the Tibetan Plateau. Samples from five major salt lakes of the Tibetan Plateau located at altitudes over 4,000 m showed clear differences from other Artemia populations in China. We also observed two consistent amino acid changes, 153A/V and 183L/F, in the COI gene between the high and low altitude species in China.Moreover, indels in the COI sequence were identified in cyst and adult samples unique to the Co Qen population from the Tibetan Plateau, demonstrating the need for additional investigations of the mitochondrial genome among Tibetan Artemia populations.