Perfumed white trumpets and stinky black stars: sensory aspects of pollinator shifts and floral evolution in the South American genus Jaborosa (Solanaceae)

MARCELA MORÉ

Grasmere

Simposio; Mini-Symposium on Sensory Aspects of Pollination; 2010

The Rank Prize Funds

Angiosperms use different types of flower signals (e.g. visual, olfactory, echo and tactile) to attract pollinators. Different pollinator agents could exert selection pressures on a wide array of floral traits affecting plant reproductive success and could, eventually, drive speciation. Thus, concerted changes in flower traits (coloration, scent composition, corolla morphology, type and amount of reward) and pollinator associations within a plant lineage provide strong evidence for adaptive evolution. The genus Jaborosa (Solanaceae) is comprised of 23 species endemic to southern South America and exhibits astonishing inter-specific variation in floral traits. This variation ranges from nocturnal white flowers with very long corolla tubes that emit pleasant odours and produce abundant nectar, to diurnal black flowers with shallow corollas, which emit unpleasant odours and produce no nectar. To infer whether Jaborosa species diversified in relation to pollinator shifts, we mapped flower traits (corolla colour, flower shape, presence of nectar, fragrance composition) and actual pollinators onto a molecular phylogeny based on data from one nuclear (GBSSIwaxy) and two chloroplast genes (trnT/trnD and trnH/psbA). Corolla colour was measured by the means of a spectrophotometer, flower morphology measurements were obtained from digital pictures, and floral fragrance composition was assessed using GC-MS. Pollinator spectrum was determined in the field by direct observations and videotaping. Multivariate analyses were employed to identify suites of traits associated with each pollinator group. Phylogenetic reconstruction of the sequence data obtained so far confirmed the monophily of Jaborosa. Two major clades were recovered, one grouping all three species that clearly exhibit a sphingophilous syndrome (J. integrifolia, J. odonelliana y J. runcinata) and the second one grouping the remaining species. Interestingly, species pollinated by carrion flies (Calliphoridae, Muscidae and Sarcophagidae) were not nested together, suggesting that transitions to miophylous flowers or possibly from these to other pollination modes have occurred multiple times in the genus Jaborosa. This is surprising, given that each transition involved co-ordination of dramatic changes in metabolic (scent composition and nectar secretion) and developmental processes (flower shape). This runs against the idea that intermediate “stepping stones” are needed to effect large changes in floral adaptation. Our results suggest that the remarkable floral diversification in the genus Jaborosa could be a product of concerted changes associated with adaptation to different pollinator agents.