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Osmoregulation pattern and salinity tolerance of the white shrimp Litopenaeus vannamei (Boone, 1931) during post-embryonic development

Mangrove forests in the Gulf of California, Mexico represent the northernmost populations along the Pacific coast and thus they are likely to be source populations for colonization at higher latitudes as climate becomes more favorable. Today, these populations are relatively small and fragmented and prior research has indicated that they are poor in genetic diversity. Here we set out to investigate whether the low diversity in this region was a result of recent colonization, or fragmentation and genetic drift of once more extensive mangroves due to climatic changes in the recent past. By sampling the two major mangrove species, Rhizophora mangle and Avicennia germinans, along the Pacific and Atlantic coasts of Mexico, we set out to test whether concordant genetic signals could elucidate recent evolution of the ecosystem. Genetic diversity of both mangrove species showed a decreasing trend toward northern latitudes along the Pacific coast. The lowest levels of genetic diversity were found at the range limits around the Gulf of California and the outer Baja California peninsula. Lack of a strong spatial genetic structure in this area and recent northern gene flow in A. germinans suggest recent colonization by this species. On the other hand, lack of a signal of recent northern dispersal in R. mangle, despite the higher dispersal capability of this species, indicates a longer presence of populations, at least in the southern Gulf of California. We suggest that the longer history, together with higher genetic diversity of R. mangle at the range limits, likely provides a gene pool better able to colonize northwards under climate change than A. germinans.

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Abstract. The rhynchoteuthion stage of the jumbo squid, Dosidicus gigas, has morphological characteristics similar to the paralarvae of the purpleback squid, Sthenoteuthis oualaniensis, making it difficult to determine the locations, seasons, and conditions where spawning of jumbo squid occurs. In this study, 180 paralarvae of D. gigas were collected off the west coast of the Baja California peninsula and identified by sequencing a 369‐bp fragment of the cytochrome oxidase I gene. Of these, 77 specimens, 0.8–6.0 mm in mantle length, were described. Indices based on morphometric ratios were used to determine whether the shapes of different body structures were reliable for identifying the paralarvae. For two ratios, the results appear to discriminate members of D. gigas from those of S. oualaniensis. Additionally, eye or intestinal photophores were not observed in any paralarvae of D. gigas. Morphological and morphometric information provided a valuable basis for the discrimination and identification of these two species.

Purple sea urchin Strongylocentrotus purpuratus is fished from British Columbia, Canada to Punta Baja, Mexico. The North American population has been divided into northern and southern fishery stocks at the break of Point Conception, but little is known about its southernmost distribution along the Mexican Pacific coast of the Baja California peninsula. In this study purple sea urchin populations in six sites along the Baja California peninsula were analyzed using mitochondrial deoxyribonucleic acid restriction fragment length polymorphism (mtDNA RFLP). A homogeneous distribution of three common haplotypes among all sites was observed. A significant FST value, however, indicated genetic structure mainly due to the haplotype array in San Miguel, Isla Todos Santos and Punta Baja sites, which were characterized by having high haplotype diversity and several unique haplotypes. Homogeneous distribution of haplotypes along the peninsula could have been influenced by the unidirectional California Current system, flowing north to south. Unique haplotypes in Punta Baja and the structure found could be the result of local oceanographic features specific to this major upwelling zone. It may be necessary to consider the Punta Baja populations individually when managing the purple sea urchin fishery in Baja California, as they show signs of being a unique stock.

The white spot syndrome virus (WSSV) is a pathogen of great concern to the worldwide shrimp culture. In comparative studies on the WSSV genome, regions such as the open reading frame (ORF) 14–15 and ORF 23–24, prone to deletions and recombination, had been useful to study the evolutive relationships among viral strains. When looking for the WSSV strains infecting Litopenaeus vannamei (Boone) in northwest Mexico, we found evidence of a genetic similarity in ORF 14–15 to a strain from India and a recombination involving ORFs 78, 79 and 80. Two genotypes were found involving the insertion of a 265 base‐pair segment of ORF 108 into ORF 78 with inversions and deletions within ORFs 78, 79 and 80. The WSSV has an Asian origin and the mutations found could be an adaptation strategy to infect L. vannamei and other crustacean species of the American continent.