Evolutionary convergence of visual and olfactory signals in a guild of night-blooming flowers pollinated by hawkmoths of southern South America

MORÉ, M.; RAGUSO, R.A.; CARMONA, D.; BENITEZ-VIEYRA, S.

Montpellier

Congreso; Second Joint Congress on Evolutionary Biology; 2018

European Society for Evolutionary Biology (ESEB), American Society of Naturalists (ASN), Society for the Study of Evolution (SSE), Society of Systematic Biologists (SSB)

Flowers announce the presence of rewards (e.g. nectar, pollen) through a combination of sensory signals (e.g. visual, olfactory, tactile) which can evoke in their pollinators innate or learned behaviors that mediate effective pollination. Thus, plant species that share a functional group of pollinators often converge upon common signals of attraction as well as similar morphology, through pollinator-mediated selection. Nocturnal hawkmoths represent one such functional group, in that they rely on a combination of visual and olfactory cues to locate sources of floral nectar, often from flowers whose nectar spurs match the lengths of their extended probosces. Here, we tested for the presence of convergent flower traits, i.e. corolla color and floral fragrance, in a hawkmoth-pollinated (sphingophilous) plant community of Subtropical South America. First, we quantitatively characterized flower color and chemical composition of floral fragrance by means of spectrophotometry and gas chromatography coupled to mass spectrometry (GC/MS), respectively. Measurements were performed on 28 plant species in 10 angiosperm families, including 14 sphingophilous species with 14 diurnally pollinated sister species used as ´phylogenetic controls´. Flower color and scent were parameterized in "phylomorphospace", i.e. mathematical ordination of floral traits within the pollinators´ sensory spaces, while controlling for phylogenetic relationships. We found strong evidence for convergent evolution in visual signals, for instance, white flowers from different species were indistinguishable within the visual space of Manduca sexta, a representative nocturnal hawkmoth and primary node in our pollination network. Meanwhile, olfactory signals showed a lesser degree of convergence, in that some volatiles (e.g. methyl benzoate) were widespread among sphingophilous species, whereas others (e.g. nitrogenous compounds) were exclusive to clade or species. Our results indicate the paramount importance of visual contrast in hawkmoth attraction and relaxed selection by hawkmoths on specific olfactory signals, supporting the potential for scent-mediated floral constancy as an alternative to strict chemical convergence.