Reciprocidade floral e morfofuncionalidade de estiletes em uma espécie enantiostílica monomórfica do gênero Senna Mill

Abstract

The occurrence of floral reciprocity between the right and left morphs in enantiostilia is necessary to stimulate the crossed pollen flow and to reduce the chances of self-fertilization. Monomorphic species, due to the occurrence of two morphs in the same individual, make geitonogamy possible, which confronts the evolutionary meaning of enantiostyly. The evaluation of reciprocity is difficult in enantiostyly, due to the lack of applied methods to measure the positioning of reproductive structures in flowers, since there are changes in the configuration of floral pieces during visits, especially in Cassiinae. Within the subtribe, atypical variations in the patterns of pollen deposition and uptake between species may also occur, which may lead to new perspectives on the group's natural history. The present work aimed to evaluate the intra and intermorphic floral reciprocity and to confront patterns of morphology and morpho-functionality of the right and left morphs of a monomorphic enantiostylic species of the genus Senna. The research was carried out in the Araripe National Forest, located in the extreme south of Ceará. A population of Senna rugosa (G. Don) H. S. Irwin and Barneby, a monomorphic enantiostylic species pollinated by vibration, was studied. We describe the variation in the position of sexual organs and use adaptive inaccuracy to infer intra and inter-morphic reciprocity. The reason for the occurrence of the different floral types was verified based on morphological and morpho-functional criteria, in addition to the guild of floral visitors, the compatibility system and pollen viability. Reciprocity patterns were not similar between flowers with right and left stigmas. Hercogamy between stigmas and pollination anthers furthest from the stylet is mainly generated by horizontal spacing, while depth is the measure that generates the greatest hercogamy with pollination anthers closer to the stylet. In left flowers, hercogamy is generated mainly by horizontal spacing, regardless of the anther considered. The individuals showed a similar proportion of the floral types considering the morphological criterion. However, considering the morpho-functionality, the proportion of flowers differed, with a lower proportion of functionally left flowers. The species was visited by seven species of bees, showed a certain level of self-compatibility and the pollen grains from the pollination and feeding anthers had high viability. Senna rugosa is the first report of a possible division of functions in pollen uptake between flowers of opposite morphs, showing variations in the morphological and morpho-functional patterns of flowers that may be linked to selective pressures such as reproductive safety and increased skills in pollen capture in stilettos in specific positions.