Date Published: February 2, 2017
Publisher: Public Library of Science
Author(s): Marilza Silva Costa, Ricardo José Silva, Hipólito Ferreira Paulino-Neto, Mônica Josene Barbosa Pereira, Fabio S. Nascimento.
The conservation and sustainable management of Annona coriacea requires knowledge of its floral and reproductive biology, and of its main pollinators and their life cycles. In this work, we analyzed these aspects in detail. Floral biology was assessed by observing flowers from the beginning of anthesis to senescence. The visiting hours and behavior of floral visitors in the floral chamber were recorded, as were the sites of oviposition. Excavations were undertaken around specimens of A. coriacea to determine the location of immature pollinators. Anthesis was nocturnal, starting at sunset, and lasted for 52–56 h. The flowers were bisexual, protogynous and emitted a strong scent similar to the plant´s own ripe fruit. There was pronounced synchrony among all floral events (the period and duration of stigmatic receptivity, release of odor, pollen release and drooping flowers) in different individuals, but no synchrony in the same individuals. All of the flowers monitored were visited by beetle species of the genera Cyclocephala and Arriguttia. Beetles arrived at the flowers with their bodies covered in pollen and these pollen grains were transferred to the stigmata while foraging on nutritious tissues at the base of the petals. With dehiscence of the stamens and retention within the floral chamber, the bodies of the floral visitors were again covered with pollen which they carried to newly opened flowers, thus promoting the cycle of pollination. After leaving the flowers, female beetles often excavated holes in the soil to lay eggs. Larvae were found between the leaf litter and the first layer of soil under specimens of A. coriacea. Cyclocephala beetles were the main pollinators of A. coriacea, but Arriguttia brevissima was also considered a pollinator and is the first species of this genus to be observed in Annonaceae flowers. Annona coriacea was found to be self-compatible with a low reproductive efficiency in the area studied. The results of this investigation provide ecological data that should contribute to the conservation and economic exploitation of A. coriacea.
The pollination ecology allows the understanding of the structure of natural plant communities [1–4] and provides information about the shape of the flowers, which makes it possible to characterize the mechanisms of pollination and adaptation of visitors to the flower . Moreover, the relationship between plant and pollinator are also important in the structuring of communities, and can influence the spatial distribution of plants in the richness and abundance of species [3, 4, 6, 7]. In the Cerrado, known for its great wealth of plant species [3, 8–12] are studies on the reproductive systems, sexual and pollination, which, these are fundamental to the understanding of the biological processes [3, 13–15].
The commencement of anthesis in A. coriacea was characterized by a slight separation between the apices of the outer petals, when it is possible to see part of the inner petals. These flowers do not expose the gynoecium and androecium even when open, since the petals recurve towards the flower center, forming a floral chamber. Anthesis occurred during the night (from 17:00 hours), and the duration of flowers ranged 52–56 hours since the separation of the outer petals from the total detachment of the stamens of the receptacle (Fig 1).
The A. coriacea flowers have a night anthesis lasting 52–56 hours. In A. coriacea, as in most species of Annonaceae, anthesis occurs in two distinct phases due to the time difference between the received stigmas and pollen release, thereby preventing self-pollination . Most species of Annonaceae studied so far are self-pollinated, but cross-pollination is essential to greater reproductive success and increased gene flow once the flowers are dichogamy [11, 18, 30, 31].
Anthesis in Annona coriacea lasted 52–56 hours, starting synchronously at nighttime. It is a cantharophilic species, considering the flower structure and the abundance and behavior of visiting beetles. The main pollinator is C. atricapilla, and its secondary pollinators are C. undata, C. ohausiana, and C. octopunctata and A. brevissima. However, future studies are needed to assess the relative importance of these species of beetles as effective pollinators. By visiting the flowers, beetles feed on pollen and nutritious tissues located at the base of the petals, copulate and pollinate the flowers. After leaving the flowers, the females dig the soil and lay eggs (in the soil below araticum tree, or a distance up to 100 meters away), in places rich in leaf litter. There the larvae remain feeding on roots and decaying material until the emergence of the adult, a period coinciding with the beginning of the next flowering. A. coriacea is a self-compatible species, and the area had low reproductive efficiency (0.42) producing less fruit coming from natural pollination than those produced under treatment of cross-pollination.