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.