The Ramírez Lab

University of California - Davis

Coevolution in the euglossine-orchid mutualism

We are interested in studying the adaptations, speciation processes, and ecological determinants of long-term evolutionary associations between bee pollinators and their host plants. To address these questions, we have investigated host specialization and co-diversification among Neotropical euglossine bees and their orchid hosts.

Euglossine bees include some of the most important insect pollinators in the New World Tropics. Male euglossine bees exhibit unique adaptations, such as specialized hind-leg pouches, for the acquisition and accumulation of odoriferous compounds (fragrances) from flowers and other sources, including orchids. During courtship display, male euglossine bees expose these fragrance mixtures, presumably to convey species-specific mate choice and/or recognition signals to females. Our research has shown that the chemical composition of male-acquired fragrances evolves rapidly during lineage diversification, thus allowing reproductive isolation among bee lineages. These specialized physiological and behavioral traits are present in all species of euglossine bees. In addition, an estimated >700 species of orchid species (family Orchidaceae) have evolved intricate adaptations-such as specialized floral fragrances and pollinator entrapment-to exclusively channel pollination services by male bees.

To elucidate the possible patterns of coevolution between euglossine bees and their orchid hosts, we have assembled a species-level phylogeny of the entire tribe Euglossini, and sequenced DNA from orchid pollinaria recovered from male bees caught in the field. We are also performing chemical analyses (GC-MS) of the fragrances collected by male bees to investigate three related questions: (1) the evolutionary changes and the role of chemical bouquets in promoting pre-zygotic reproductive isolation in orchid bees; (2) the utility of male-gathered fragrances as informative characters for discerning cyrptic species; and (3) the underlying genetic and neuro-physiological mechanisms that govern chemical differentiation among closely related (cryptic) species.