Introgressive hybridization between two close speciesSiniperca chuatsiandSiniperca kneri(Percomorpharia: Sinipercidae) in the Middle Reaches of the Yangtze River

Abstract

Siniperca chuatsiandSiniperca kneriare two economically important freshwater fishes endemic to East Asia. Recently, someSinipercaspecimens 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 betweenS. chuatsiandS. 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 twoSinipercaspecies, 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 (FST = 1) betweenS. chuatsiandS. kneriwere selected and verified for species diagnosis. A total of 349 loci with 458 diagnostic SNPs were identified for discriminatingS. chuatsiandS. 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 asS. chuatsiand 32 specimens asS. 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 bothS. chuatsiandS. 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 ofSinipercaspeies 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 betweenSinipercaspecies in the future.