How specialised is bird pollination in the Cactaceae?

Area of Science:

• Botany
• Ecology
• Evolutionary Biology

Background:

• Many cactus species possess ornithophilous (bird-pollinated) flowers, yet their reproductive biology remains largely unstudied.
• The genus Cleistocactus is recognized for its bird-pollinated species, suggesting potential specializations for avian pollination.

Purpose of the Study:

• To investigate the pollination systems of two Cleistocactus species, Cleistocactus baumannii and Cleistocactus smaragdiflorus.
• To assess the degree of specialization for bird pollination in cacti and its prevalence within the family.
• To re-evaluate previous studies on bird pollination in cacti.

Main Methods:

• Observational studies of floral visitors and pollination interactions.
• Analysis of floral traits associated with ornithophily.
• Comparative review of existing literature on cactus pollination.

Main Results:

• Both Cleistocactus species displayed ornithophilous floral traits.
• Cleistocactus baumannii was exclusively pollinated by hummingbirds.
• Cleistocactus smaragdiflorus was pollinated by both hummingbirds and bees, indicating a less specialized system.
• Bird pollination is documented in 27 cactus species, many with ornithophilous traits but often generalist pollination systems.
• Reddish flowers, associated with diurnal anthesis and tubular shape, occur in 27% of cactus species.

Conclusions:

• Phenotypic specialization for bird pollination is common in cacti, but it does not guarantee functional or ecological specialization.
• Cactus pollination systems can be complex, with species often interacting with multiple pollinator groups beyond birds.
• Further research is needed to fully understand the reproductive biology and pollination ecology of diverse cactus species.