Examining differentiation of sympatricSchizothoraxfishes reveals low differentiation in internal compared to external feeding traits

Abstract

In the process of sympatric species differentiation, which feeding traits are most differentiated? The complete feeding process of capture, ingestion, and digestion requires certain external, as well as internal traits. Therefore, comprehensive comparisons are needed to study fish feeding habits. This study systematically investigated the adaptive radiation and parallel evolution of Schizothorax fishes, and quantified the external, frame, pharyngeal bone, and digestive traits of the systematically differentiated omnivorous Schizothorax davidi and herbivorous S. wangchiachii. A member of their sister genus, the carnivorous Percocypris pingi, was used as an outgroup control to explore the feeding differentiation of sympatric Schizothorax fishes. The results showed that these species had highly differentiated external traits, while the internal traits (pharyngeal bone and digestive traits) showed low differentiation, indicating that predatory traits diverged first in the differentiation of sympatric Schizothorax fishes, while chewing and digestive traits were slower to diverge. Furthermore, we screened 16 continuous feeding traits, and the quantified values of these traits progressively increased or decreased with increasing nutritional level of food. These findings provide a reference for the selection of quantitative indicators in future studies of sympatric species differentiation.