Mitochondrial DNA and microsatellite analyses reveal strong genetic differentiation between two types of estuarine tapertail anchovies (Coilia) in Yangtze River Basin, China.

The estuarine tapertail anchovy might comprise a "paired species" of Coilia nasus (which has declined sharply) and Coilia brachygnathus (dominant in some lakes). It has previously been debated whether C. nasus and C. brachygnathus constitute two distinct species or anadromous and freshwater-resident ecotypes. Here, we studied the genetic structure of these species by analyzing the mitochondrial gene cytochrome b (Cyt b) and polymorphic microsatellite loci in 184 anchovies and discriminated their migratory life history using otolith microchemical analysis. Bayesian analysis and a discriminant principal components analysis showed two distinct genetic clusters that corresponded to C. nasus and C. brachygnathus, and we revealed the presence of hybridization between the two closely related sister species. C. nasus has higher genetic diversity within a population and lower genetic divergence between populations than C. brachygnathus. No significant genetic differentiation was detected between the migratory and freshwater-resident C. brachygnathus or between the migratory and freshwater-resident C. nasus. These phenomena suggest that C. brachygnathus and C. nasus are different species, and a strong but permeable reproductive barrier may exist. Both these species have migratory-resident ecological dimorphism, and C. brachygnathus is predominantly a resident species, whereas C. nasus is predominantly an anadromous species. [ABSTRACT FROM AUTHOR]