Pollination and reproductive system of synchronopatric species of Cactaceae (Cactoideae) subject to interspecific flow of pollen: an example of ecological adaptation in the Brazilian Chaco.

Abstract

Three synchronopatric Cactaceae species, Echinopsis rhodotricha, Harrisia balansae and Praecereus saxicola, have mostly nocturnal anthesis and similar flowers, characteristics that motivated us to perform a comparative study of reproductive ecology. Reproductive phenology was sampled monthly from December 2014 to November 2015. We describe floral biology, breeding system via pollination treatments and evaluate floral visitors from focal and filming observations. Pollen grains found on moth proboscis were compared among cactus species under light microscopy. We used fluorescent dye particles to test intra- and interspecific pollen flow. These three species have extended flowering with greater intensity in the wet season, causing high overlap. They have white and hypocrateriformis flowers that open at twilight or nightfall and last about 15h. H.balansae seems to be self-incompatible, while E.rhodotricha presented self-compatibility. P.saxicola presented self-fertility, but most of the population seems to be self-incompatible. We suggest sphingophily for the three species, but only P.saxicola was visited by Manduca rustica (Sphingidae). However, we observed pollen grains of all three species on the proboscis of moths, especially M.rustica and M.sexta. Prolonged anthesis allowed bees (herein considered as secondary pollinators) to visit flowers of E.rhodotricha and P.saxicola. It can be concluded that the studied species share nocturnal and diurnal pollinators, suggesting interspecific pollen flow, which, however, could not be detected with fluorescent dye particles. In view of the low frequency of primary pollinators, it appears that these three species have different reproductive strategies, ensuring the fruiting and production of viable seeds.