Reproductive biology and floral visitors of Collaea cipoensis (Fabaceae), an endemic shrub of the rupestrian grasslands

Abstract

Plant interactions with flower visitors are essential to understand the reproductive biology, evolution and distribution of flowering plants. Morphological convergences of flower traits have allowed flowers to maximize their attraction to pollinator agents leading to the concept of pollination syndromes. Due to habitat heterogeneity, low water retention and resource availability in the soil, as well as broad altitudinal range of the system, plants often show restricted distributions in rupestrian grasslands. The present study aimed to describe the floral biology and reproductive aspects of Collaea cipoensis, a shrub restricted to small patches alongside watercourses in rupestrian grasslands of Serra do Cipó, Brazil. Specifically, we examined the dependence on pollinators to set fruits and the functional role of floral visitors (i.e. pollinators, nectar-robbers, nectar-thieves, and florivores). Collaea cipoensis is a strictly xenogamous species and two hummingbirds (Colibri serrirostris and Eupetomena macroura) are its potential pollinators. Although C. serrirostris also behaves as illegitimate visitor, it represents 90% of legitimate visits, thus being the most important pollinator. However, the most common flower visitors are two important nectar-robbers, the bee Trigona spinipes and the syrphid Toxomerus musicus. The species is self-incompatible and pollen-limited, as hand-pollination increased fruit production more than 50%. Still, hand-pollination set only 20% of fruits and 48% of seeds. Overall, the dependence on cross-pollination, the stressful environmental conditions and the high floral visitation rates by illegitimate visitors may limit reproduction of this species, leading to a fitness reduction. Our results reinforce the idea that rupestrian grasslands conform a complex scenario that restricts the species distribution.