Polinização por formigas em Microstachys serrulata (Mart. & Zucc.) Müll. Arg. (Euphorbiaceae) no Cerrado

Abstract

Zoophily or biotic pollination is very frequent and presents specifics mutualistic associations between flowers and insects or vertebrates. Insects are the most important pollinators, mainly those of the order Hymenoptera and especially the bees. Ants are known as predators, collectors of extrafloral nectar, seeds dispersers, only the reproductive ants are winged, and many species have the metapleural gland that produce substances able to chemically disturb pollen viability. Nevertheless, some ant species without this gland can act as effective pollinators in shrubs and herbs of arid environments. Our objectives were to investigate the pollination ecology of Microstachys serrulata (Mart. & Zucc.) Müll Arg. (Euphorbiaceae), a common shrub in Brazilian savanna, with small, inconspicuous flowers, odorless, and without studies about its reproductive biology. . Plants were observed in the ecological reserve of Clube de Caça e Pesca Itororoó de Uberlândia, in two phytophysiognomies: ‘campo sujo’ and ‘cerrado sensu stricto’. We found five orders of insect visiting the flowers and ants were the main pollinators. The biggest abundance of ants, especially Camponotus crassus, ensured a fructification as effective as natural pollination, which visitation carried out freely by the animals. Although a minor fructification can happen after apomixis (in the absence of pollen) and eventual pollination by distinct insects, is not enough to maintain the species in the environment. The pollen-ovule ratio observed and compared with Cruden (1977) indicates that the species is facultatively autogamous and the low fructification observed after apomixis and spontaneous self-pollination reinforces the need of biotic pollination. The studied system presents ants as the main pollinators directly responsible to maintain the plant population in the environment. Therefore, we suggest that more studies need to be made in arid environments such as those found in Brazilian savanna, to better explore the still underestimated mutualistic associations between ants and flowers.