Variation in chromosome number and breeding systems: implications for diversification in Pachycereus pringlei (Cactaceae).

Polyploidy, the possession of more than two sets of chromosomes, is a major biological process affecting plant evolution and diversification. In the Cactaceae, genome doubling has also been associated with reproductive isolation, changes in breeding systems, colonization ability, and speciation. Pachycereus pringlei (S. Watson, 1885) Britton & Rose, 1909, is a columnar cactus that has long drawn the attention of ecologists, geneticists, and systematists due to its wide distribution range and remarkable assortment of breeding systems in the Mexican Sonoran Desert and the Baja California Peninsula (BCP). However, several important evolutionary questions, such as the distribution of chromosome numbers and whether the diploid condition is dominant over a potential polyploid condition driving the evolution and diversity in floral morphology and breeding systems in this cactus, are still unclear. In this study, we determined chromosome numbers in 11 localities encompassing virtually the entire geographic range of distribution of P. pringlei. Our data revealed the first diploid (2n = 22) count in this species restricted to the hermaphroditic populations of Catalana (ICA) and Cerralvo (ICE) Islands, whereas the tetraploid (2n = 44) condition is consistently distributed throughout the BCP and mainland Sonora populations distinguished by a non-hermaphroditic breeding system. These results validate a wider distribution of polyploid relative to diploid individuals and a shift in breeding systems coupled with polyploidisation. Considering that the diploid base number and hermaphroditism are the proposed ancestral conditions in Cactaceae, we suggest that ICE and ICA populations represent the relicts of a southern diploid ancestor from which both polyploidy and unisexuality evolved in mainland BCP, facilitating the northward expansion of this species. This cytogeographic distribution in conjunction with differences in floral attributes suggests the distinction of the diploid populations as a new taxonomic entity. We suggest that chromosome doubling in conjunction with allopatric distribution, differences in neutral genetic variation, floral traits, and breeding systems has driven the reproductive isolation, evolution, and diversification of this columnar cactus.

Microsatellite variability analysis in farmed catfish (Ictalurus punctatus) from Tamaulipas, Mexico

Analysis of cultured catfish from six farms in Tamaulipas, Mexico was achieved using a combination of microsatellite PCR analysis and semiautomatic fluoresce-based detection, in order to provide a first assessment of the genetic variability on cultured catfish in Mexico. Five microsatellites showed extensive polymorphism with allele numbers ranging from 10 and 20. Overall observed heterozygosity at each locus ranged between 0.76 and 0.91 and the average polymorphic information content (PIC) for the five loci was 0.811, indicating that these loci can be used for studies of paternity identification, linkage and population genetics. On the basis of the F ST values (F ST = 0.03829; p = 0.00000) it appears that there was a small amount of genetic differentiation between the channel catfish stocks. The high intrapopulation allelic diversity was the most remarkable parameter.