Biologia reprodutiva de duas espécies de Palicourea Aubl. (Rubiaceae) em floresta de terra firme na Amazônia Central

Abstract

The plants are part of biodiversity and source of energy for several organisms that may act positively or negatively on their reproductive success. During the reproduction, most plants interact with pollen vectors and other herbivores, affecting the pollination output and fruit and seed set. The objectives of this study are describing the reproductive biology of Palicourea corymbifera and P. nitidella (Rubiaceae) in the Amazon forest understory, and evaluating the roles that flower visitor species and the presence of ants play on pollination and fruit production by these two plant species. Fieldwork was carried out in the forest reserve Adolpho Ducke, Manaus, Amazonas, between November 2014 and January 2016. Flowering of P. corymbifera started in June and peaked in September when the first individuals started to fruit, whereas flowering of P. nitidella started in September and the fruit season in November. Populations of both plant species presented distyly, but P. nitidella included two additional semi-homostylic morphs, named here as “brevistyle variant” (VB) and “longistyle variant” (VL). Palicourea corymbifera and P. nitidella were self-incompatible, although the variant morphs presented 1 to 2% of fruits produced through geitonogamy. The VB and VL morphs showed peculiar relations of incompatibility between them and with other morphs, once VL was compatible with brevistyle and VB pollen but not compatible with pollen from VL or longistyle morphs. Flowers of the two species were diurnal, tubular and odourless; nectar sugar concentration ranged from 17 to 26%. Hummingbirds, bees and butterflies visited P. corymbifera and P. nitidella flowers. Based on visiting behaviour and contact with anthers and stigmas, hummingbirds were the main pollinators and some bees were nectar or pollen robbers. Thirteen and ten ant species patrolled and fed on the extrafloral nectaries of P. corymbifera and P. nitidella inflorescences, respectively. Through experiments with controlled ant presence/absence, fruit set showed increased success in inflorescences with presence of ants than in those with ants absent. However, the composition of flower visitor assemblages and the total number of visits per flower did not significantly differ between inflorescences with presence or absence of ants. On the other hand, visitor assemblages significantly differed between P. corymbifera and P. nitidella in spite they shared several visitor species. In addition, the total number of bee- and butterfly-visits per flower was higher in P. nitidella than in P. corymbifera inflorescences, but the number of hummingbird-visits per flower was not different between them. In overall, the presence of ants has no perceptible effects on flower visitor species of Palicourea or on their visiting frequencies, thus the increased fruit set in the presence of ants seems to be related to the protection that ants may confer against other herbivores. The high frequency of bees, which are likely less efficient for legitimate pollinations, could explain the occurrence of semi-homostylic morphs in P. nitidella.