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.

Connective appendages in Huberia bradeana (Melastomataceae) affect pollen release during buzz pollination

“…Another indicator of appendages not functioning in pollinator attraction is the lack of a colour contrast between appendages and other floral parts, as it is common in other Melastomataceae species (Fig. 1; Velloso et al 2018; Dellinger et al 2019). We did not assess visitation rate and hence did not directly test for the attraction function of appendages.…”

“…However, surprisingly little is known about their functional role in the pollination process (Buchmann 1983; Hermann & Palser 2000). Several functions have been proposed, such as that colourful or scented stamen appendages may increase floral attractiveness to pollinators (Luo et al 2008; Velloso et al 2018; Solís‐Montero et al . 2018), reward pollinators (Dellinger et al 2014), serve as handles for buzzing bees when applying vibrations or help to position pollinators to optimize pollen transfer (Beattie 1971; Augspurger 1980; Renner 1989; Endress 1994; Han et al 2008; Luo et al 2008).…”

A sophisticated case of division of labour in the trimorphic stamens of theCassia fistula(Leguminosae) flower

“…Pollen flowers are generally pollinated by bees and offer a surplus of pollen as an exclusive reward to pollinators instead of nectar and other floral resources ( Vogel 1978 ). In pollen flowers, pollen grains (male gametophytes) act directly as the transport agent of the male gamete ( Arroyo 1981 ; Pacini 2000 ; Lersten 2004 ; Barrett 2010 ), pollen grains also comprise the diet of larvae of insects, especially bees, as a primary floral resource sought out by pollinators ( Agostini et al 2014 ).…”

“…The recurrent and independent evolution of pollen flowers ( sensu Vogel 1978 ) in multiple angiosperm families ( Buchmann 1983 ) implies the appearance of strategies that circumvent the ‘pollen dilemma’ in these plant lineages ( Westerkamp 1996 , 1997 ). Indeed, plant species bearing pollen flowers have several features to deal with the ‘pollen dilemma’.…”

“…Indeed, plant species bearing pollen flowers have several features to deal with the ‘pollen dilemma’. For instance, pollen flowers can show polystemony (large number of stamens in relation to other floral parts) or larger anthers compared to flowers with other resources ( Vogel 1978 ; Cruden 2000 ), both increasing pollen grains per flower to guarantee enough pollen for the two conflicting functions ( Agostini et al 2014 ). Additionally, pollen flowers commonly have poricidal anthers, controlling pollen release at each floral visit in a contingency strategy known as buzz pollination ( Buchmann 1983 ; Harder and Barclay 1994 ; Vallejo-Marín 2019 ).…”