Genetic diversity and population genetic structure of three endemic species of Mammillaria (Cactaceae) from the Tehuacán Valley in central México.

Mammillaria hernandezii, M. dixanthocentron and M. lanata are endemic and threatened cactus species that inhabit the Tehuacán Valley, an arid zone in southern México that has an important richness of cacti. Their populations have been exposed to habitat alteration and poaching. Available information regarding genetic diversity is limited, but necessary for their conservation, and collection and use of germplasm. We used microsatellite markers to determine genetic diversity and population genetic structure of six populations of M. hernandezii, four of M. dixanthocentron and a single recorded population for M. lanata. The levels of heterozygosity were moderate in the three species (M. hernandezii Ho = 0.46, M. dixanthocentron Ho = 0.45 and M. lanata Ho = 0.52), with significant differences in their allelic richness. The genetic differentiation between populations was significant in M. hernandezii (R_ST 0.22) and M. dixanthocentron (R_ST 0.17), with evidence of isolation by distance in M. dixanthocentron. Geographic isolation and inbreeding are the processes that seem to shape the genetic variability of populations and differentiation in these species. We identified three genetic groups for M. hernandezii, and five groups for M. dixanthocentron. Conservation and protection must be guaranteed in all three species, with special emphasis on populations with high genetic diversity and private alleles. Finally, we recommended establishing a program for the development of germplasm banks, to promote Mammillaria ssp. propagation as an emerging measure of ex situ conservation. [ABSTRACT FROM AUTHOR]