Abstract: To explore the effects of life history stage on geometric morphology of nationally protected Brachymystax tsinlingensis and its sympatric Phoxinus lagowskii, lateral photographs of both species at different life history stages were collected. The thin-plate spline models were then established by using the Tps software. The geometric morphological characters were extracted and corrected with the formula Y=lgA_i/lgA. The intra and inter-specific differences of relative geometric morphological characters were statistically analyzed, and principal component analyses in each species were performed. The results showed that the background grids of overall structural framework of the two species at different life history stages had varying degrees of bending in the head, back, abdomen, and tail. The geometric morphological characters of B. tsinlingensis and P. lagowskii differed significantly between species (P<0.05). The life history stage effect had significant influence on the geometric morphological characteristics of both species (P<0.05). Results of principal component analysis showed that there were no overlapped samples of B. tsinlingensis and only a few overlapped samples of P. lagowskii at PC1 and PC2 levels in different life history stages. The samples of both species at different life history stages formed relatively concentrated groups. In conclusion, there were significant inter and intra-specific differences in the geometric morphology of B. tsinlingensis and P. lagowskii. Special consideration should be given to life history stage effects in future taxonomic identification, population conservation as well as the differentiation and adaptation studies based on geometric morphological characters.

Key words: Brachymystax tsinlingensis, Phoxinus lagowskii, life history stage, sympatric species, geometric morphology