Cross-species amplification of microsatellites reveals incongruence in the molecular variation and taxonomic limits of the Pilosocereus aurisetus group (Cactaceae).

The Pilosocereus aurisetus group contains eight cactus species restricted to xeric habitats in eastern and central Brazil that have an archipelago-like distribution. In this study, 5-11 microsatellite markers previously designed for Pilosocereus machrisii were evaluated for cross-amplification and polymorphisms in ten populations from six species of the P. aurisetus group. The genotypic information was subsequently used to investigate the genetic relationships between the individuals, populations, and species analyzed. Only the Pmac101 locus failed to amplify in all of the six analyzed species, resulting in an 88 % success rate. The number of alleles per polymorphic locus ranged from 2 to 12, and the most successfully amplified loci showed at least one population with a larger number of alleles than were reported in the source species. The population relationships revealed clear genetic clustering in a neighbor-joining tree that was partially incongruent with the taxonomic limits between the P. aurisetus and P. machrisii species, a fact which parallels the problematic taxonomy of the P. aurisetus group. A Bayesian clustering analysis of the individual genotypes confirmed the observed taxonomic incongruence. These microsatellite markers provide a valuable resource for facilitating large-scale genetic studies on population structures, systematics and evolutionary history in this group.

Isolation, characterization, and cross-species amplification of polymorphic microsatellite markers for Pilosocereus machrisii (Cactaceae).

PREMISE OF THE STUDY: Microsatellite primers were developed in Pilosocereus machrisii, a columnar cactus with a patchy distribution in eastern tropical South America, to assess its genetic diversity and population structure. METHODS AND RESULTS: Eleven microsatellite markers were developed, of which one was monomorphic among 51 individuals from two populations. The number of alleles per polymorphic locus ranged from two to eight, and the total number of alleles was 57. From the 11 isolated loci, nine were successfully amplified in the other four Pilosocereus species. CONCLUSIONS: The results showed that these markers will be useful for studies of genetic diversity, patterns of gene flow, and population genetic structure in P. machrisii, as well as across other congeneric species.