Abstract
Divergent selection among environments affects species distributions and can lead to speciation. In this article, we investigated the transcriptomes of two ecotypes of scaleless carp (Gymnocypris przewalskii przewalskii and G. p. ganzihonensis) from the Tibetan Plateau. We used a transcriptome sequencing approach to screen approximately 250,000 expressed sequence tags (ESTs) from the gill and kidney tissues of twelve individuals from the Ganzi River and Lake Qinghai to understand how this freshwater fish has adapted to an ecological niche shift from saline to freshwater. We identified 9,429 loci in the gill transcriptome and 12,034 loci in the kidney transcriptome with significant differences in their expression, of which 242 protein-coding genes exhibited strong positive selection (Ka/Ks > 1). Many of the genes are involved in ion channel functions (e.g., Ca2+-binding proteins), immune responses (e.g., nephrosin) or cellular water absorption functions (e.g., aquaporins). These results have potentially broad importance in understanding shifts from saline to freshwater habitats. Furthermore, this study provides the first transcriptome of G. przewalskii, which will facilitate future ecological genomics studies and aid in the identification of genes underlying adaptation and incipient ecological speciation.
Highlights
Freshwater lake connected to the Yellow River
Geologic data indicates that approximately 1.2 Ma BP the Yellow River emerged at the edge of the plateau, and approximately 0.15 Ma BP the “Gonghe Movement” of the Tibetan Plateau led to the separation of Lake Qinghai from the upper reaches of the Yellow River, after which Lake Qinghai became an occlusion lake[14,15]
While historical sources indicate that the Ganzi River once flowed into Lake Qinghai, an additional survey, conducted in 1964, revealed that the lake lacked a connection to the Ganzi River, likely reflecting the shrinking of the lake shoreline and low flows in the upper reaches[16]
Summary
Freshwater lake connected to the Yellow River. Geologic data indicates that approximately 1.2 Ma BP the Yellow River emerged at the edge of the plateau, and approximately 0.15 Ma BP the “Gonghe Movement” of the Tibetan Plateau led to the separation of Lake Qinghai from the upper reaches of the Yellow River, after which Lake Qinghai became an occlusion lake[14,15]. The scaleless carp is a cold-water-adapted freshwater fish, narrowly distributed in Lake Qinghai Basin in China[19]. We sequenced the transcriptomes of the two ecotypes of G. przewalskii inhabiting the freshwater Ganzi River and the saltwater Lake Qinghai to study the changes in their transcriptomes that may be adaptations to the different environments in which they live.
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