Floral Variation, Nectar Production, and Reproductive Success of Two Drymonia (Gesneriaceae) Species with Mixed Pollination Syndromes

Abstract

Premise of research. Pollination syndromes are suites of correlated characters that reflect selection by most frequent and effective pollinators. However, the floral phenotypes of some angiosperm species combine traits from different pollination syndromes. The aim of this study was to assess the correspondence between floral traits and floral visitors, considering the breeding systems of two co-occurring Drymonia species with mixed floral phenotypes.Methodology. We assessed floral morphology, nectar production patterns, frequency of floral visitation, breeding systems, and natural fruit set in Drymonia strigosa and Drymonia oinochrophylla species at Los Tuxtlas, Veracruz, Mexico, during 2011–2014. We also conducted a field test of reproductive assurance in D. strigosa, the only species with a high potential for autonomous self-pollination.Pivotal results. In D. strigosa, morphology and nectar production patterns correspond to the ornithophilous syndrome; however, anthers have poricidal dehiscence, a trait associated with bee pollination. Hummingbirds were the most frequent floral visitors, and stingless bees were less frequent visitors acting mostly as nectar robbers. The species has a high autofertility potential, but autonomous self-pollination contributed little to fruit set during the study years. In D. oinochrophylla, most floral traits correspond to the melittophilous syndrome; however, high nectar production and large flower size resemble traits of chiropterophilous flowers. Primary pollinators were bees with less frequent visits by butterflies and moths; bats were not observed during the study period. Drymonia oinochrophylla is self-compatible, but it has little potential for autonomous self-pollination; therefore, seed production is highly dependent on pollinators.Conclusions. Our results suggest that mixed floral phenotypes in the two Drymonia species are not likely a consequence of visitation by multiple pollinator functional groups. Instead, incomplete correspondence of floral traits with classic pollination syndromes may represent undetected floral visitors in disturbed environments or plesiomorphies retained throughout the evolutionary history of the genus Drymonia.