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

Abstract

Species of Opuntia (prickly pears), widely propagated for human use, are present in many agroforestry systems. Like other perennials, they are subject to environmental pressures that influence their reproductive ecology and reproductive output. Here, we studied floral biology, breeding system, and flower-bee interactions of Opuntia atropes, which is subject to management, to better understand its reproductive ecology. We documented floral phenology, morphology, and mating system by observing live flowers, measuring fixed flowers, and performing pollination treatments. We recorded frequency, behavior, and floral visitors’ handling time to determine the most effective pollinator. Opuntia atropes has large, herkogamous flowers and high P/O ratios. These traits promote outcrossing, which was supported by the results of pollination treatments. Fruit weight and seed set exhibited moderate pollen limitation. Floral visitors comprised nine bee species. Diadasia sp. was the most effective pollinator according to frequency and behavior. Opuntia atropes shows preferential outcrossing through pollination by a specialist bee despite being in a modified habitat. Pollen limitation and variation in reproductive success may lead to mating system evolution in O. atropes. The observed bee diversity suggests that O. atropes is an important source of floral resources in the dry season in semi-arid environments under moderate human disturbance.

Keywords:
Opuntia; native bees; effective pollinator; bee diversity; floral biology; cactus; tropical dry forest