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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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Trypsin from Pacific white shrimp Litopenaeus vannamei is a polymorphic protein composed of three alleles (A, B, and C). The C allele is monomorphic for the first region, while A and B are allelic variations for the second region that are segregated according to Mendelian rules. These three alleles give rise to three individual trypsin phenotypes displayed in sodium dodecyl sulfate polyacrylamide gel electrophoresis: CBA, CB, and CA. The expected frequencies from mating CBA males and females resulted in offspring that consisted of 25% CB, 25% CA, and 50% CBA trypsin phenotypes. To define a management protocol for studying shrimp performance associated with the trypsin phenotype, the goal of this study was to determine if the expected proportions of the three trypsin phenotypes are represented in the population structure at breeding age in 11 hatcheries. Here, we hypothesized that the population structure of the trypsin phenotypes is represented by frequencies that are subject to selection, and it is possible to establish a management protocol to study shrimp performance. A total of 2,828 breeding shrimp from 11 hatcheries were analyzed to describe their population structure. The results showed a high frequency of CBA breeders and a near absence of the CA phenotype in the population structure. To discard the possibility that man‐made selection is the cause of the trypsin phenotype frequency, the offspring of CBA breeders were cultured in nine commercial ponds, and the phenotype frequencies were monitored during 75 d. Interestingly, the CA phenotype was only present during the early stages of culture, which suggests that the population structure is not due to human selection of CBA shrimp in the hatcheries. In this condition, poslarvae production could be directed to make trials that contribute to describe the difference between the culture performance between phenotypes, but not to support the commercial production of larvae with the highest culture performance trypsin phenotype.

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