Phenology, reproductive biology and diversity of buzzing bees of sympatric Dichorisandra species (Commelinaceae): breeding system and performance of pollinators

摘要

This paper reports on phenology, breeding system and dependence on pollinators of two sympatric Dichorisandra species. Dichorisandra incurva is a chamaephyte with continuous growth and precocious flowering, whereas D. hexandra is a geophyte with seasonal growth and delayed flowering. Flowering and fruiting occur mainly in the wet season; thus moisture can be important for both species. Besides moisture, photoperiod seems also to be related to the flowering only of D. incurva. Flowers of both species are poricidal, oligandrous, zygomorphic and buzz-pollinated by Apidae and/or Halictidae bees. Dichorisandra incurva is self-compatible, while D. hexandra shows a late-acting self-incompatible system. Moreover, herkogamy and poricidal anthers prevent spontaneous self-pollination in D. incurva. Therefore, medium- to large-sized Apidae are the most suitable pollinators as they make regular contact with anthers and stigmas and are further known to perform trapline foraging. This behaviour is particularly important for D. hexandra where Halictidae are considered pollen robbers, thus wasting pollen which, consequently, causes low reproductive efficacy in this species. Nevertheless, bee diversity is probably advantageous for the reproductive success of both Dichorisandra species. While the efficiency of each bee species is not known, further studies will show whether additional benefits are gained from the maintenance of these interactions.