Browningia candelaris (Meyen) Britton & Rose, a self-incompatible cactus pollinated by hummingbirds and insects in the Atacama Desert

Abstract

Browningia candelaris is a cactus from the Atacama Desert with bat pollination syndrome (i.e., chiropterophilia). In Peru, the bat Platalina genovensium appears to be its main pollinator. However, in Chile, this bat only inhabits the Azapa Valley, being the pollinators and the reproductive system of B. candelaris unknown in the south of its distribution (e.g., Tarapacá). Through manual pollination trials, in 2017 and 2019, we evaluated the ability of B. candelaris to produce fruits and seeds with its own pollen, but without pollinators (i.e., autogamy), with its own pollen and pollinators (i.e., geitonogamy), and with exogenous pollen and pollinators (i.e., xenogamy). In addition, we evaluated natural pollination and the identity of pollinators. The autogamy flowers did not bear fruits, indicating that B. candelaris is unable to produce seeds in the absence of pollinators. Through geitonogamy there was only 20% fruiting, although only in one year, indicating a low capacity for self-pollination mediated by pollinators. About 75% of the flowers fructified by xenogamy indicating that cross pollination is the main reproductive mechanism. However, the xenogamy fruiting was 10% higher than the natural one, and the number of seeds per fruit 34.3% higher, which indicates a low effectiveness of the pollinators. The potential pollinators are the northern hummingbird (Rhodopis vesper vesper) and seven species of insects (3 Diptera, 3 Hymenoptera, 1 Lepidopteran). Additional studies on the pollination and reproduction of threatened desert plants seem to be mandatory to propose appropriate conservation strategies.