Mating system of a Mammillaria magnimamma (Cactaceae) population of the semi-arid central Mexican region

Abstract

Knowledge on the reproductive biology of globose cacti in the genus Mammillaria is incipient, despite being one of the most diverse and threatened groups in Cactaceae. We studied a clonal population of Mammillaria magnimamma (Hawort) located in the Valle del Mezquital, Mexico in which sexual reproduction occurs, although neither seedlings nor juveniles were observed. Based on their short life cycle, globose life form, and melittophilous pollination syndrome, this species was expected to exhibit a mixed mating system and null seed recruitment. We examined the population structure, reproductive phenology, and the mating system by means of controlled-pollination experiments (autonomous self-pollination, manual self-pollination, manual outcross pollination and open pollination). We tested for differences between treatments in the number of seeds per fruit and estimated outcrossing rates. Most (88%) of the M. magnimamma population consisted of clones (10.6 stems/ind) and no juvenile plants or seedlings were recorded. Seed were produced in all the experimental treatments. The average number of seeds per fruit was significantly higher (χ2 = 29.52; d.f. = 3; P < 0.0001) in the outcross than the self-pollination treatments. Outcrossing rates estimated from fruits, te, fruits = 0.829, and seeds, te, seeds = 0.8774, showed that M. magnimamma exhibits a mixed mating system. Despite the large number of seed produced, the persistence of these populations likely depends on clonal reproduction. The null recruitment and elevated anthropogenic pressure that this species undergoes across its distribution range threaten its populations.