Adaptive Evolution of the Eda Gene and Scales Loss in Schizothoracine Fishes in Response to Uplift of the Tibetan Plateau

Schizothoracine is the predominant wild fish subfamily of the Tibetan plateau (TP). Their scales, pharyngeal teeth and barbels have gradually regressed with increasing altitude. Schizothoracine have been divided into three groups: primitive, specialized and highly specialized. Ectodysplasin-A (Eda) has been considered as a major gene that contributes to the development of skin appendages. The present study cloned the Eda genes of 51 Schizothoracine fish species which represent the three groups and five Barbinae species. Phylogenetic analyses indicated that Eda may have acted as the genetic trigger for scale loss in the Schizothoracine. Furthermore, 14 single nucleotide polymorphisms (SNPs) and two deletions (18 bp and 6 bp in size), were also detected in the Eda coding sequence of the highly specialized group compared to the primitive group. The same SNPs and two indels result in four non-synonymous and two G-X-Y and 1 XY motif indels, which possibly contribute to significant structure changes in the Eda gene. The domain including (G-X-Y)(n) motif in the Eda gene is relatively conserved amongst teleosts. Based on the above results, we hypothesize that the evolution of Eda gene might be associated with the scale loss in Schizothoracine fishes in response to the phased uplift of the TP.