The Similarity of Floral Scent Composition in Two Breynia Species Pollinated by the Same Host-Specific Epicephala Moth

Abstract

Floral scent has been thought to play a critical role in the obligate pollination–seed consumption mutualism between Breynia (Phyllanthaceae) species and Epicephala moths. The two closely related Breynia species, B. fruticosa and B. Rostrata are jointly pollinated by the same moth species (E. lativalvaris and E. mirivalvata), which has led to an obligate pollination mutualism of ‘two-to-two’ species specificity. However, empirical data on host floral volatiles as chemical cues maintaining the plant−moth specificity are missing. In the present study, 27 volatile compounds were identified from floral scents of the two Breynia species. A total of 25 compounds were shared jointly by the two species, and only one compound, β-humulene, was species specific and exclusively produced by B. fruticosa. The two Breynia species clearly showed no interspecific floral scent profiles within both sexes, especially in male flowers. Male and female flowers of floral scent from these plants exhibited major qualitative differences, and male flowers produced more scent than female flowers. For male flowers of B. fruticosa, there was significant temporal variation in the volatile chemical profiles and total floral scent emission before and after pollination. Interestingly, β-phenylethyl butyrate and phenylethyl alcohol were present in maximal amounts during pollination, but they rapidly reduced in concentration after pollination. The findings suggest that the similar floral scent profiles of the two Breynia species reflect adaptations to the same pollinator, Epicephala, for their pollination. Sexually dimorphic floral scent between male and female flowers has been selected to provoke pollinator’s active pollination behavior on host flowers. Temporal changes in floral scent of male flowers before and after pollination may have evolved to limit the overexploitation of the ovaries by seed predators, Epicephala moths. We speculate that the two most abundant compounds in the male flowers, β-phenylethyl butyrate and phenylethyl alcohol, may be two signal compounds to attract Epicephala in a species-specific manner.