Geographic variation in floral scent of Echinopsis ancistrophora (Cactaceae); evidence for constraints on hawkmoth attraction

Abstract

Variation in floral phenotype (color, depth, nectar) suggests incipient specialization for bee or hawkmoth pollination across the geographic distribution of Echinopsis ancistrophora, with flower depth ranging from 4.5 to 24 cm. We used chemical and behavioral analyses to test whether fragrance has evolved in concert with morphology in these Andean cacti. Floral scent (145 total compounds) was collected using dynamic headspace methods and analyzed with gas chromatographyÁmass spectrometry, revealing subspecies-specific odors dominated by sesquiterpenes in E. ssp. ancistrophora and arachnacantha and fatty acid derivatives or aromatics in E. ssp. cardenasiana and pojoensis. Compounds indicative of sphingophily were not consistently found in moth-pollinated plants, and total scent emissions were significantly lower in populations with nocturnal anthesis. In wind tunnel assays, Manduca sexta moths were attracted to scent of ssp. ancistrophora from both bee and hawkmoth-pollinated populations, but not to scent of ssp. cardenasiana. However, hawkmoths were most attracted to the methyl benzoate-dominated scent of a distant relative, Echinopsis mirabilis. Thus, hawkmoth-pollinated descendants of the E. ancistrophora lineage may be phylogenetically constrained to emit weak, sesquiterpene-dominated fragrances that are not optimally attractive to hawkmoths, or floral scent may be under stronger selection by destructive flower visitors.

Spatial and temporal variation in volatile composition suggests olfactory division of labor within the trap flowers of Aristolochia gigantea

“…4.20) and were tentatively identified using NIST, Wiley, and Adams mass spectral libraries (see Schlumpberger and Raguso, 2008). When possible, peak identity was confirmed using authentic standards.…”

Geographical matching of volatile signals and pollinator olfactory responses in a cycad brood-site mutualism

“…As for morphological floral traits, scent properties of a species can vary geographically [9] in a manner which can be clinal [10] or unstructured [11], continuous or discrete. Possible explanations for this geographical variation include phenotypic plasticity, local hybridization, neutral processes such as genetic drift, and adaptive processes such as coevolution or pollinator shifts [4,9,12].…”

Flowering Phenology and Observations on the Pollination Biology of South American Cacti. 1.Denmoza rhodacantha

“…In recent years, evidence is accumulating, however, that in many cases, other than the pollinators predicted by the syndrome are in effect, either in addition to, or instead of the expected ones. This has opened the door to a general criticism of the value of pollination syndromes, especially as analysis of flower characteristics showed that almost no flowers fit the pre-defined syndromes precisely (Ollerton et al 2009, see also Schlumpberger &Raguso 2008 andSchlumpberger et al 2009 for detailed studies on the lability of the expression of pollination syndromes at a population-level context of cacti). Also, there is a rapidly increasing body of investigations that found "multi-purpose flowers", i.e.…”