Discussion
The species differentiation events between G. przewalskii andC. carpio occurred at 24.06 Mya ago based on the phylogenetic analysis. This period coincides with the second tectonic uplift of the Qinghai-tibet plateau (25~17 Mya) affected by Himalayan orogeny, resulting in an average elevation of up to 2000m (Shi, et al. 1999; Wang, et al. 2014). In addition, the complex geography, such as the appearance of sedimentary basins (Qaidam basins, 27Mya; Yumen basins, 25Mya; Linxia basins, 29Mya) surrounding the Qinghai lake, had intensified the barriers to communication among species before the Early Yellow River formation (from late Middle Pleistocene to Holocene) (Fang, et al. 2003; Han, et al. 2013; Ding, et al. 2014; Wang, et al. 2014). We advanced a hypothesis that some primordial ancestor of Cyprinidae fish which were isolated from the population and remained on the plateau side had evolved to Schizothoracine fish.
The unique gene analysis found that most of these genes enriched in pathways participating in membrane transport and immune defense, such as bile secretion, ABC transporters, cell adhesion molecules. The migration between freshwater river and saline-alkaline lake requires G. przewalskii deal with profound physiology changes in acid–base balance and osmoregulation. For example, the bile secretion pathway plays an important role in bicarbonate secretion and proton uptake in the bile and liver, which may aid naked carp in compensating for a respiratory alkalosis during saline-alkaine water adaptation (Yao, et al. 2016). With respect to the immune response, the innate immune system provides a fundamental barrier to preventing pathogen entry into the fish body (Whyte 2007). As one of the physical components of the innate immune system, fish scales provide a protective barrier against viruses and bacteria in a variety of environments, effectively preventing infection and fighting off disease (Ellis 2001; Magnadottir 2006, 2010). However, scaleless fishes have lost this protective barrier, so they might have to enhance other biological functional pathways such as cell adhesion molecules to replenish the protective deficiency associated with the loss of scales.