Volume 66, June 2016, Pages 63–75
Highlights
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- Semen scented Xysmalobium parviflorum flowers produce large amounts of 1-pyrroline.
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- Sweaty scented X. tysonianum produce isovaleric acid and several foetid aliphatics.
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- X. asperum scent dominated by epoxy oxoisophorone with other terpenoids and aromatics.
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- Clear variation in scent chemistry between populations of X. parviflorum.
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- Minimal overlap between total scent profiles of 8 Xysmalobium species.
Abstract
Floral
volatiles play an important role in plant communication with both
pollinators and antagonists, but remain poorly explored for many plant
groups. Asclepiads (Apocynaceae: Asclepiadoideae subtribe Asclepiadinae)
represent a diverse group in South African grasslands, but the scents
of most species remain unexplored and few genera are sufficiently
sampled to allow comparisons between congeners. I used dynamic headspace
extraction methods and coupled gas chromatography-mass spectrometry
(GC–MS) to examine the scent chemistry of three unusually scented
asclepiads in the genus Xysmalobium and then combined these
data with previously published data to explore inter- and intraspecific
variation in the genus. A total of 74 compounds (33–44 per species) from
various compound classes were detected in the species examined here.
The sweet but faintly foetid scent of Xysmalobium asperum was dominated by epoxy oxoisophorone in combination with various other terpenoids and aromatics, and small amounts of p-cresol. The sweat-like scent of Xysmalobium tysonianum
was dominated by a few aromatics in combination with isovaleric acid
and several aliphatic compounds normally associated with microbial
degradation or fermentation. The semen-like scent of Xysmalobium parviflorum
flowers examined here contained large relative amounts of 1-pyrroline,
and comparison with previously published data for dung-scented flowers
from a different population revealed clear divergence in the relative
amounts of this compound and p-cresol. I also detected 25 compounds that were not shared between the two X. parviflorum populations. Comparison of scent data for eight Xysmalobium
species revealed very distinct chemical profiles with limited overlap
between species. These results are discussed in relation to the possible
roles of these volatiles as pollinator attractants and the evolution of
floral scents within the genus.
Keywords
- Chemotypes;
- 3,4-dihydro-2H-pyrrole;
- Fermentation volatiles;
- Intraspecific variation;
- 3-Methylbutanoic acid;
- Oviposition-site mimicry;
- Oxoisophoroneoxide;
- Sapromyiophily
© 2016 Elsevier Ltd. All rights reserved.
