Reproductive ecology and inbreeding depression in Opuntia rastrera (Cactaceae) in the Chihuahuan Desert: why are sexually derived recruitments so rare?
Mandujano M. del C. | Montana C. | Eguiarte L.E.
We evaluated the influence of the reproductive ecology on low recruitment of sexually derived progeny observed in Opuntia rastrera Weber in the Southern Chihuahuan Desert, in two vegetation types. The flowers are diurnal, remaining open 9-10 hr. Pollen is released in the morning and at the same time the stigmas become receptive. Nectar is produced all day, but the production rate is higher at noon. The flowers are visited by insects, mainly solitary bees (Diadasia sp. and Lithurge sp.). Floral characteristics and the pollen/ovule ratio suggest that Opuntia rastrera is a facultative xenogamous species. Controlled pollinations indicate that it is not apomictic and pollinators are required to set fruit; it is also self-compatible, but there is strong inbreeding depression for fruit set. However, we were unable to demonstrate differences in reproductive characters between the populations in both vegetation types. The average density of adults per hectare was one order of magnitude higher in the nopalera (Opuntia-dominated scrublands) than in the grassland. However, the average density of plants that originated from seeds was one order of magnitude lower in the nopalera. Opuntia rastrera produces abundant flowers, fruits, and seeds in both vegetation types in natural conditions. The low success in the recruitment of new genets cannot be ascribed to the reproductive ecology.
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