Morphologic and genetic characterization of wild populations of shrimp of the genus Penaeus within the Gulf of California, Mexico: New social, political, and management dilemmas for the Mexican shrimp fishery

Species are often composed of discrete breeding units called populations, demes, or stocks. Each stock, while not reproductively isolated from other conspecific populations, may have limited opportunities to interbreed with others due to geographic separation. Allopatric stocks are favored, fortuitously arise, or become extinct, through differential selective pressures (including fishing and disease) acting either locally or throughout the geographic range of a species. Usually, these selection processes result in genetic and morphological dissimilarities between stocks. Whereas changes in the genotype are commonly reflected in the morphology of the individual, shifts in morphology do not always result from alterations of the genotype; morphological change can be induced by environmental factors (phenotypic plasticity). Therefore, it is essential to combine morphological with genetic analyses in studies of wild population identification. The goals of my research were to identify and characterize morphological stocks of Penaeus stylirostris and P. vannamei in the Gulf of California, and to conduct genetic analysis on the identified morphotypes of P. stylirostris to confirm their population structure. Seventy-eight variables were obtained from 417 specimens of P. stylirostris (representative of 21 fishing grounds) and 218 P. vannamei (representing 14 fishing grounds) and analyzed by principal component and canonical variate analyses. Morphometric analysis revealed three distinct regional stocks of P. vannamei and five of P. stylirostris. Genetic structure of P. stylirostris populations was tested from 78 samples (representing six fishing grounds in the Gulf) of male total genomic DNA extracted from frozen shrimp tails. The DNA samples were adjusted in distilled water to a final concentration of 10 ng/mul, and amplified with 20 random 10-mer primers (Operon) on a Perkin Elmer Thermocycler. The PCR RAPD profiles were used to identify between stock genetic differences. The novel adoption of sequencing gels to analyze RAPD profiles, proved useful in demonstrating (significant) genetic differences between specimens from all six fishing grounds. My research demonstrates the importance and applicability of combining morphological and genetic analyses in studies of wild stock identification. The relevance of my findings to the management of the Mexican shrimp fishery and the aquaculture industry are thoroughly discussed