Variability in mating strategies in a widespread cactus in the Chihuahuan Desert

Abstract

Opuntia is the most diverse and widespread genus in the Cactaceae; several species have broad distribution ranges and have successfully adapted to distinct habitats. One explanation for their success is the diversity of their reproductive systems. Opuntia macrocentra is one of the most common widespread species in North American deserts. A previous work on a northern population documented that this species has a mixed‐mating system and receives a low frequency of pollinators. In a southern population of O. macrocentra, we described its floral visitors, anthesis schedules and flower morphometry. Through controlled pollination experiments (selfing, outcrossing, supplementary pollen and natural pollination), we assessed the breeding and mating systems and measured pollen limitation. Eight different bee species visited the flowers. Based on their conduct, Diadasia rinconis and Lasioglossum sp. were the main pollinators. Flowers were homogamous and herkogamous. Floral traits and pollination experiments showed that O. macrocentra is xenogamous and self‐incompatible. Fruit set of the natural pollination, outcrossing and supplementary pollen treatments were not statistically different. Seed set was higher in natural pollination and the pollen limitation index for seed set was negative. Based on these results, we conclude that O. macrocentra is not pollen limited in the studied population. These results contrast with those of the previously studied population; therefore, we caution about making generalizations about the reproductive system based solely on studies in one population. The diversity of mating systems displayed by O. macrocentra may explain its broad distribution and adaptation to different environmental factors, one of which may be pollinator availability. Our results highlight the need to describe the reproductive ecology of populations instead of species, because reproductive systems and ecological factors such as plant–animal interactions may differ across their distribution range.

Reproductive ecology of the prickly pear Opuntia atropes, a native plant subject to management

“…In addition, thigmonastic stamens could prevent inefficient pollinators from accessing the nectar chamber and the innermost and most rewarding anthers (Cota-Sánchez et al 2013). These results indicate that O. atropes is specialized for bee pollination, conducted by an Opuntia specialist bee, as has been documented for other species of prickly pears (Ortiz-Martínez et al 2022). Floral traits, like the thigmonastic stamens, provide further support for the idea of phenotypic specialization of the flower (Ollerton et al 2007) as documented in the epiphytic cactus Rhipsalis neves-armondii (Martins & Freitas 2018).…”

“…1) and its size (Table 1), as described for other Opuntia species in which effective pollinators are medium to large bees (Fachardo & Sigrist 2020). This solitary bee belongs to a genus whose preferred host is Opuntia (Sipes & Tepedino 2005;Ortiz-Martínez et al 2022). In O. atropes, the halictids (Augochlorella sp.…”

“…Furthermore, repeated outcrossing with their wild counterparts (a frequent phenomenon in Opuntia) precludes the fixation of sterility genes (McKey et al 2010). Although outcrossing mating systems are expected in Opuntia, there have been documented several Opuntia species with mixed mating systems (Mandujano et al 2010), as well as species with variation in their mating systems across populations (Ortiz-Martínez et al 2022). This diversity of mating systems in prickly pears could have evolved in response to environmental pressures such as pollen limitation, resource limitation, and/or the frequency of clonal propagation.…”