Effect of Reproductive Modes on the Population Dynamics of an Endemic Cactus from Cuatro Ciénegas

Desert plants have several adaptations to cope with harsh environmental conditions; these adaptations range from the ability to store water to the diversification of reproductive modes, displaying sexual reproduction and clonality. Grusonia bradtiana is an endemic cactus from Coahuila which dominates vegetation at bajada landforms of Cuatro Cienegas. The species reproduces sexually by seeds and clonally by fission of stems, allowing the parent plant to create genetically identical offspring. The type of recruitment influences the structure and dynamics of the population as well as the life history attributes that determine population growth. Negative environmental impacts can modify the reproductive success of plants; genotypic variation and sexual reproduction are reduced under stressful conditions while clonality is favored. Furthermore, the amount and quality of offspring via sexual reproduction decreases with high clonality, as inbreeding has negative genetic effects or if species are self-incompatible. However, clonality allows population growth or stability in harsh environments, although it may limit genotypic diversity. We studied the effect of sexual and clonal reproductive modes on the population structure and dynamics of G. bradtiana in two contrasting populations with different management history. The populations were located at Sierra de la Fragua [FRA-disturbed site], and at Sierra de San Marcos y Pinos [SMP-conserved site] in Cuatro Cienegas Basin. Population structure of G. bradtiana is similar between studied populations, despite their management history. In contrast, we found a higher density of individuals of G. bradtiana at SMP population, where clonal reproduction predominated, compared to FRA. According to our predictions, sexual fecundity was higher in individuals of all reproductive categories in SMP, where the sexual reproductive strategy predominates, while production of seeds was lower at FRA population due to strong inbreeding depression in the species. Interestingly, combination of both reproductive strategies allows populations to remain numerically stable.