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 (Ps 89.5%), with high numbers of alleles per polymorphic locus (APs 3.82), but moderate levels of heterozygosity (Hes 0.145). Substantial levels of inbreeding were detected across loci and populations at macrogeographic (FIS 0.348) and regional levels (FIS 0.194–0.402). Moderate levels of genetic dierentiation among populations were detected at macrogeographical (FST 0.193) and regional (FST 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