Interspecific Variation of Floral Scent Composition in Glochidion and its Association with Host-specific Pollinating Seed Parasite (Epicephala)
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Trees of the genus Glochidion (Phyllanthaceae) are pollinated by females of Epicephala moths (Gracillariidae) whose larvae consume the seeds of the flowers that they pollinate. Each Epicephala moth species is specific locally to a single host species, although two to four Glochidion hosts often cooccur. To investigate the role of olfactory signals in maintaining the plant−moth specificity, we analyzed floral scent composition of five Glochidion species by using gas chromatography–mass spectrometry (GC-MS) and conducted Y-tube olfactometer bioassays with Epicephala moths and their host flowers. The GC-MS analysis showed that the floral scents of the five Glochidion species are dominated by (R)-(−)- and (S)-(+)-linalool, and (E)- and (Z)-β-ocimene, and that each species produces 6–20 compounds. Transformation of scent profiles by using chord-normalized expected species shared distances and analysis of the data with nonmetric multidimensional scaling showed that floral volatiles of cooccurring Glochidion species can be distinguished by relative chemical composition, especially that of minor compounds. The bioassay with pollinators of Glochidion lanceolatum and Glochidion ruburm further indicated that Epicephala moths are capable of discriminating their hosts by using floral odor. The results suggest that the floral scent of Glochidion is one of the important key signals that mediate the encounters of the species-specific partners in the Glochidion–Epicephala mutualism.
KeywordsBioassay Epicephala Floral scent Glochidion Obligate pollination mutualism Species specificity
We appreciate Y. Inui for providing the opportunity to conduct this study; T. Y. Chiang, T. W. Hsu, and S. C. Liu for assistance in the field in Taiwan; Y. Yamaoka and I. Shimizu for allowing us to use the GC and GC-MS; Y. Kumano and N. Fujiwara-Tsujii for technical advice in collecting and analyzing the floral scents; and the subject editor and anonymous reviewers for valuable comments on the manuscript. This work was supported by Grant-in-Aid for Scientific Research 15370012 from Japan Ministry of Education, Culture, Sports, Science and Technology (to M. K.) and by Grant for Basic Science Research Project from Sumitomo Foundation (to T. O.).
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