Molecular population structure of the kuruma shrimp Panaeus japonicus in western Pacific

The kuruma shrimp Penaeus japonicus Bate, 1888 is widely distributed throughout the Indo-West Pacific (IWP). Two morphologically similar varieties, I and II, are recognized from the South China Sea. The two varieties are characterized by different color banding patterns on the carapace, but there are no distinct differences in morphometric traits between them based on measurement of 13 characters. Sequence data and restriction profiles of mitochondrial (mt) DNA markers reveal that these two varieties represented distinct clades, with sequence divergences of about 1% (473 bp) in 16S rRNA, 6-7% (504 bp) in cytochrome oxidase I (COI), and 16-19% (470 bp) in the control region (CR). Geographical distribution of the two varieties in the South and East China Sea was investigated by analyzing specimens collected from Japan and Singapore. Shrimps from Japan and Singapore have been found to belong to varieties I and II, respectively, suggesting that the two varieties have different geographical distribution. Phylogenetic study reveals that the two varieties are more closely related to each other than to the other phylogenetically related Penaeus species. Analysis of amplified fragment length polymorphism (AFLP) does not reveal any evidence of hybridization between these two genetically closed varieties. Results from this study conclude that two cryptic species of the kuruma shrimp P. japonicus coexist in western Pacific.;The biogeographic distribution of the two varieties was further studied on shrimp from 10 localities in western Pacific. Two Mediterranean populations are also included for comparison. Based on the mtDNA sequence data, the shrimps are separated into two distinct clades representing the two varieties. Variety I comprises populations from Japan and southern China (including Taiwan), while variety II consists of populations from Southeast Asia (Vietnam, Singapore and the Philippines), Australia and the Mediterranean. Population structure is evident in variety II, as supported by restriction profiles of two mtDNA markers (COI and CR) and analysis of two microsatellite loci. The Australian population is genetically diverged from the others, whereas the Southeast Asian and Mediterranean populations show a close genetic relationship. Variety I does not occur in these three localities, while a small proportion of variety II was found along the northern coast of South China Sea and Taiwan, which constitute the sympatric zone of the two varieties. The present study reveals high genetic diversity of P. japonicus. Further studies on the genetic structure of this species complex, particularly the populations in the Indian Ocean and Mediterranean, are needed not only to understand the evolutionary history of the shrimp, but also to improve the knowledge-based fishery management and aquaculture development programs of this important biological resource.