Genetic variation and population structure of the mixed-mating cactus, Melocactus curvispinus (Cactaceae)

Genetic diversity was measured in the mixed-mating cactus, Melocactus curvispinus , in Venezuela. Allozyme diversity was surveyed in 19 putative loci over 18 populations. Compared to other plant taxa, this cactus is rich in polymorphic loci ( P s =89.5%), with high numbers of alleles per polymorphic locus ( AP s =3.82), but moderate levels of heterozygosity ( H es =0.145). Substantial levels of inbreeding were detected across loci and populations at macrogeographic ( F IS =0.348) and regional levels ( F IS =0.194–0.402). Moderate levels of genetic differentiation among populations were detected at macrogeographical ( F ST =0.193) and regional ( F ST =0.084–0.187) scales, suggesting that gene flow is relatively restricted, but increases within regions without topographic barriers. The population genetic structure observed for this cactus was attributed to, at least, three factors: short-distance pollination and seed dispersal, the mixed-mating condition of the species, and genetic drift. High genetic identities between populations ( I =0.942) supported the conspecific nature of all populations surveyed. The levels and patterns of genetic structure observed for M. curvispinus were consistent with its mating system and gene dispersal mechanisms.