Introgressive hybridization between two close species Siniperca chuatsi and Siniperca kneri (Percomorpharia: Sinipercidae) in the Middle Reaches of the Yangtze River

Abstract

Siniperca chuatsi and Siniperca kneri are two economically important freshwater fishes endemic to East Asia. Recently, some Siniperca specimens collected from Lake Poyang and Lake Dongting in the middle reaches of the Yangtze River couldn't be clearly identified as they showed intermediate morphological characteristics between S. chuatsi and S. kneri, and some inter-species hybrids were detected by microsatellite loci. To further verify genetic composition of these intermediate individuals, and determine the prevalence and degree of introgression between the two Siniperca species, a large set of high-quality, independent, diagnostic genetic markers were necessarily required. Based on enrichment and sequencing of target genes in sinipercid fishes, 463 loci (F_ST = 1) between S. chuatsi and S. kneri were selected and verified for species diagnosis. A total of 349 loci with 458 diagnostic SNPs were identified for discriminating S. chuatsi and S. kneri. From those markers, 224 diagnostic SNPs (only one SNP per locus) were selected to identify and categorize 48 specimens with intermediate morphological characters. The results showed that there were 8 specimens identified as hybrids, 8 specimens as S. chuatsi and 32 specimens as S. kneri. NEWHYBRIDS analysis showed that the hybrid offsprings were composed of the first-generation hybrid (2 individuals), first-generation backcross (1 individual), second-generation backcross (1 individual) and fourth-generation backcross (4 individuals), and the backcrossing could happen to both S. chuatsi and S. kneri. These hybrids could occur naturally, or escaped from farmed fish, due to extensive artificial breeding practice in these regions. However, the origin of the introgressive hybridization can't be easily traced. Therefore, some measures for protecting genetic resource of Siniperca speies in the Yangtze River should be enforced, such as assessing genetic background of the cultured stocks, reducing the escapement from farmed fish, and monitoring the trend of introgressive hybridization between Siniperca species in the future.