The Pacific White shrimp, Penaeus vannamei, has a geographic distribution
covering approximately 6400km from Mexico to Peru. Within the Pacific coast of
Mexico P. vannamei can be found from Topolobampo, Sinaloa, to the Guatemalan border, crossing the biogeographical provinces of Cortez and Panama and a variety of environmental and topographical features. An examination of the genetic population substructure of P. vannamei in Mexico was performed using RAPD analysis and mtDNA PCR RFLP analysis of a 4.3kb mtDNA fragment.
RAPD analysis suggests that a northern Gulf of California and a southern Gulf
of Tehuantepec populations exists in agreement with the positions of the Cortez and Panamanian provinces, respectively. RAPD analysis also identified P. californiensis and P. stylirostris species specific RAPD markers, a highly divergent and homogeneous P. vannamei population at Topolobampo and specific marker absence within the Laguna Superior P. vannamei population.
The analysis of mtDNA PCR RFLP of the 4.3kb mtDNA fragment gave support to the north/south population subdivision indicated by the RAPD analysis. RFLP of the 4.3kb mtDNA fragment also identified a private composite haplotype with an unexpectedly high frequency in a shallow isolated lagoon in Oaxaca. The high
frequency of the private composite haplotype was attributed to selection within
extreme environmental conditions and thus the composite haplotype was believed to be of importance for the identification of hardy P. vannamei for mariculture.
Mantel Tests found significant correlations with both geographic distance and
sea surface temperature, and genetic distance estimates. Furthermore, Mantel Tests of the correlation between geographic distance and most genetic distance estimates confirm the strong divergence of P. vannamei at Topolobampo from P. vannamei in the rest of Mexico.
The population subdivision of the northern and southern P. vannamei
populations suggests that both should be included as separate stocks in fisheries management. The strongly divergent populations in Laguna Superior and particularly at Topolobampo, suggest that they may be physically isolated and thus caution should be used during the exploitation of these populations in a fisheries management policy that includes Mexico as one stock.