EVOLUTIONARY PATTERN AND ADAPTIVE STRATEGIES OF KEY MORPHOLOGICAL AND ECOLOGICAL CHARACTERS IN THE ACIPENSERIFORMES

In this study, we downloaded complete mitochondrial genome sequences of 27 Acipenseriformes species, with Polypteriformes species as outgroups, to construct molecular phylogenetic trees. Based on these trees, we analyzed macroevolutionary pattern of 12 morphological and ecological traits with the phylogenetic comparative methods (PCMs), such as reconstructing ancestral character states, analyzing character phylogenetic constraints and testing the character correlations. The results showed that 8 traits such as habitat, body size, dorsal fin rays, anal fin rays, posterior dorsal fin scutes, posterior anal fin scutes, gill rakers and egg size, were phylogenetically constrained, indicating that the evolution of these characters were associated with phylogeny and strongly affected by natural selection. Four traits including diets, female first maturity age, male first maturity age and spawning interval, showed no phylogenetic signals, indicating their adaptations to the environments. Reconstruction of ancestral character states showed that many Acipenseriformes species exhibited a pattern of evolution from the intermediate state of ancestral species evolving to two directions: becoming larger and smaller respectively. For example, body size, dorsal fin rays, anal fin rays, first maturity age all showed this pattern. For the adaptive strategies, the Acipenserformes showed the constraints of some morphological characters such as gill rakers, egg size and the flexible adaptations to different environments for the coordinating ecological characters such as diets, first maturity age, egg size, spawning interval. Results of this study can provide valuable information for understanding macroevolutionary pattern of the Acipenseriformes and give hints for species conservation.