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

Genetic diversity was measured in the mixed-mating cactus, Melocactus curvi spinus, in Venezuela. Allozyme diversity was surveyed in 19 putative loci o ver 18 populations. Compared to other plant taxa, this cactus is rich in po lymorphic 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 detecte d at macrogeographical (F-ST = 0.193) and regional (F-ST = 0.084-0.187) sca les, suggesting that gene flow is relatively restricted, but increases with in regions without topographic barriers. The population genetic structure o bserved for this cactus was attributed to, at least, three factors: short-d istance pollination and seed dispersal, the mixed-mating condition of the s pecies, and genetic drift. High genetic identities between populations (I=0 .942) supported the conspecific nature of all populations surveyed. The lev els and patterns of genetic structure observed for M. curvispinus were cons istent with its mating system and gene dispersal mechanisms.