Division of work on anthers of Microlicia cordata (Spreng.) Cham. (Melastomataceae)

Microlicia stands out among the Melastomataceae because it presents well pronounced heterantry, characteristic that is usually associated as a solution to the "pollen dilemma". Since pollen is the only resource offered in these species, its use in feeding pollinators decreases the number of viable gametes for reproduction. Thus, there would be a division of labor in plants with heterantry, in which the anthers would have different functions, one would be used to feed the bees and another would act in the pollination. Microlicia cordata, an abundant species in the study area, has two cycles of stamens, the antesepalous cycle (pollination) with magenta anthers and the antepetalous cycle (feeding) with yellow anthers. In this study, the division of labor between the anthers was analyzed using different parameters involving the anatomy and morphology of anthers and pollen grains, quantity and viability of pollen grains as well as coloring of floral structures. It has been found that the anthers of the pollination stamens are larger than the anthers of the feeding stamens, although they are similar anatomically. There is a difference in the amount of pollen grains produced in the anthers of the different cycles, but there is no difference in viability. Pollen grains with little or no cytoplasmic content were observed in the anthers of both cycles. Color analysis showed that anthers of pollination stamens have less contrasting color to the corolla, and are probably less attractive to visitors. However, the anthers of the feeding stamens and the ventral appendage of the connective of the pollinating stamens have greater contrast with the corolla, which allows to conclude that they reflect the same color to the pollinators. These results support the model of division of labor between anthers, particularly related to the quantity of pollen grains available and the coloring of floral pieces.CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorDissertação (Mestrado)Microlicia destaca-se dentre as Melastomataceae por apresentar heteranteria bem pronunciada, característica que costuma ser associada como solução ao “dilema de pólen”. Visto que o pólen é o único recurso oferecido nessas espécies, sua utilização na alimentação dos polinizadores diminui o número de gametas viáveis para a reprodução. Sendo assim, havería uma divisão de trabalho em plantas com heteranteria, na qual as anteras teriam funções diferentes, um conjunto serviría para alimentação das abelhas e outro conjunto atuaria na polinização. Microlicia cordata, espécie abundante na área de estudo, possui dois ciclos de estames, o ciclo antessépalo (polinização) com anteras magenta e o ciclo antepétalo (alimentação) com anteras amarelas. Neste estudo, o modelo de divisão de trabalho entre as anteras foi analisado utilizando-se diferentes parâmetros envolvendo anatomia e morfologia das anteras e dos grãos de pólen, quantidade e viabilidade dos grãos de pólen bem como coloração das estruturas florais. Verificou-se que as anteras dos estames de polinização são maiores que as anteras dos estames de alimentação, embora sejam similares anatomicamente. Existe diferença na quantidade de grãos de pólen produzidos nas anteras dos diferentes ciclos, porém não há diferença na viabilidade. Grãos de pólen com pouco ou nenhum conteúdo citoplasmático foram observados nas anteras de ambos os ciclos. A análise de cores mostrou que anteras dos estames de polinização têm coloração menos contrastante com a corola, sendo provavelmente menos atrativas aos visitantes. Porém, as anteras dos estames de alimentação e o apêndice ventral do conectivo dos estames de polinização têm maior contraste em relação à corola, o que permite concluir que refletem a mesma cor aos polinizadores. Esses resultados apoiam o modelo de divisão de trabalho entre anteras, particularmente no que se refere à quantidade de grãos de pólen disponíveis e à coloração das peças florais

Anther specializations related to the division of labor in Microlicia cordata (Spreng.) Cham. (Melastomataceae)

ABSTRACT In heterantherous flowers, some anthers have an attraction and feeding function, while others are related to plant reproduction. Microlicia cordata has dimorphic stamens organized in two cycles: the antesepalous one with large stamens and pink anthers, and the antepetalous one with small stamens and yellow anthers. Division of labor was analyzed using the parameters of structure, composition, amount and estimated viability of pollen, and the color of floral parts. The anthers of the pollinating stamens were larger than the anthers of the feeding stamens, although anatomically similar. There was a difference in the amount of pollen produced by the anthers of the two cycles, but no difference was found in pollen viability. Considering a bee color vision model, the color of the anthers of the pollinating stamens contrasted less with that of the corolla, and thus is probably less attractive to visitors. Conversely, the anthers of the feeding stamens and the ventral appendage of the connective of the pollinating stamens contrasted more with the corolla, presenting the same color to the pollinators. These results are in accordance with the idea of division of labor among anthers of heterantherous flowers, especially regarding the quantity of pollen and the color of the floral parts