Insurance against reproductive failure in a semelparous plant: bulbil formation in Agave macroacantha flowering stalks

Abstract

Bulbils are small aerial rosettes that occur on the flowering stalks of semelparous Agave plants and in related families, and that are capable of acting as clones of the parent plant. We hypothesized that bulbil formation was inversely related to fruiting success in the flowering stalk, and we explored this hypothesis in A. macroacantha, a species from South-Central Mexico. Forty randomly chosen plants were divided amongst three treatments: (a) elimination of all floral buds, (b) exclusion of pollinators, and (c) control. We also studied 22 plants in which the flowering stalk had been felled by goat grazing. Between September and November 1991 we kept a record of the numbers of bulbils and capsules produced in each flowering stalk. Significant (P<0.0001) differences between treatments were found in the proportion of plants hearing capsules and bearing bulbils. The control treatment had the highest proportion of plants producing capsules, treatment a had the highest proportion of individuals bearing bulbils, while treatment b showed an intermediate response. In the goat-grazed group, 45% of the plants failed to produce any propagative structure after the stalk was cut, and half of all plants produced bulbils on the remaining stump. A significant inverse relationship between the numbers of capsules and the numbers of bulbils per plant was found for the three randomly assigned treatments. Our results suggest that once the production of the flowering stalk has been triggered and the death of the rosette is irreversible, bulbils may act as an insurance mechanism that increases the probability of successful reproduction of the genet.

Demographic analysis of <em>Agave angustifolia</em> (Agavaceae) with an emphasis on ecological restoration

“…In Agave marmorata, for instance, stalk removal had an important impact on several demographic processes (fecundity, growth, and seedling establishment) resulting in a lower λ value compared to a population where no stalks were severed (Jiménez-Valdés et al 2010). In addition, many Agave populations present mast seeding years (Arizaga and Ezcurra 1995), which would be a further source of demographic variation through time.…”

Invasion of Agave species (Agavaceae) in south‐east Spain: invader demographic parameters and impacts on native species

“…Throughout their life span, agaves produce rhizomes, the apical meristems of which give rise to new individuals (Arizaga & Ezcurra, 2002; Infante et al ., 2003). Another clonal mechanism of reproduction occurs in floral stems, where bulbils are developed from sterile meristems (Arizaga & Ezcurra, 1995; Arizaga & Ezcurra, 2002).…”

Spatial distribution pattern of a clonal species: effects of differential production of clonal and sexual offspring

“…The ability to generate clonal descendants by plantlets occurs in several species in a number of families (Crassulaceae, Oxalidaceae, Polygonaceae, Saxifragaceae, Agavaceae, Bromeliaceae, Poaceae, Juncaceae, Liliaceae, and Gesneriaceae; Elmqvist and Cox 1996). In the Cactaceae it has only been reported in other species of genus Opuntia and Cylindropuntia: C. kleiniae, O. rufida, C. imbricata, O. phaeacantha, C. leptocaulis, O. spinosibacca, O. tunicata (Anthony 1954) and O. echios (Hicks and Mauchamp 1999) and has been considered an insurance mechanism against sexual reproductive failure (Arizaga and Ezcurra 1995;Palleiro et al 2006).…”