Diversification in both the floral morphology and chemistry in two daciniphilous orchid ecotypes in Borneo

Abstract

Morphological and floral chemical components are both important cues used by plants to attract pollinators. Two local ecotypes named ‘Nabawan’ and ‘Apin-Apin’ produced by the tropical orchid, Bulbophyllum ecornutum subspecies verrucatum, exhibit different morphology and scents to attract males of certain Bactrocera and Zeugodacus fruit fly species in the tribe Dacini as potential pollinators. Flowers of the Nabawan-ecotype possess a narrow-shaped lip (= labellum) structure and emit a characteristic fragrance of raspberry ketone along with smaller amounts of rhododendrol, whereas those of Apin-Apin-ecotype possess a broad-shaped lip and emit zingerone and zingerol as major components. Nevertheless, the structure of stiff hamulus appears similar and acts as a ‘crowbar’ during pollinarium removal by a fruit fly, indicating the basic mechanics of the movable see-saw lip structure to trap a fly is essentially the same. The changes in both morphology and chemistry, despite no significant difference in chloroplast DNA sequences, shown by the two ecotypes, might have occurred as part of a coevolutionary process involving both the Dacini fruit fly pollinators and the Bulbophyllum orchids in their natural habitats.