A Novel Interplay Between Orchids and Fruit Flies: Scientists Uncover First-of-its-Kind Plant-Animal Symbiosis

A previously unobserved symbiotic relationship between the orchid Gastrodia foetida and its pollinating fruit fly, both primarily subsisting on fungi, has been discovered. The orchid emits an odor akin to mushrooms, attracting the flies. As the flies forage on the flowers, pollen grains adhere to their dorsal surface (1). As the insect departs one bloom to lay eggs in another, the affixed pollen makes contact with the receiving flower’s stigma, accomplishing pollination (2). Subsequent to successful pollination, the flower commences its decomposition while internally developed larvae start to consume the petals (3). The larvae continue their growth by feeding on fallen petals (4). Around a week later, they mature into adult flies. Credit: ANSAI Shun

This groundbreaking discovery marks the first documented instance of “nursery pollination” in orchids, signifying a potential evolutionary shift towards a mutualistic relationship between plants and animals.

Orchids have been traditionally noted for deceiving their pollinators by mimicking food sources, mating sites, or even partners, without actually offering any genuine rewards. The fungi-dependent, non-photosynthetic orchid genus Gastrodia typically employs such deception, emitting a scent resembling rotting fruits or decaying mushrooms to attract fruit flies of the Drosophila species.

The fruit flies are enticed into the flower, momentarily trapped, and subsequently bear pollen on their backs, which they carry to other plants of the identical species, thereby benefiting solely the plant.

Plant biologist Suetsugu Kenji from Kobe University, an expert on these specific orchids, observed that Gastrodia foetida has unusually fleshy petals that degrade and detach a few days post-pollination. Intrigued, he set out to examine these plants as a potential inaugural instance of orchids practicing “nursery pollination,” where the plant furnishes a breeding site for its pollinator.

Recent research, now published in the journal Ecology, reveals that these flies regularly deposit their eggs in the orchid’s blooms, providing an environment conducive to the full development of the larvae into adult flies.

Suetsugu highlights an arresting detail: despite being commonly referred to as ‘fruit flies,’ the Drosophila bizonata species, specialized in fungi consumption, mainly utilize the decaying petals of Gastrodia foetida for breeding. This is possibly because the orchid, which is a fungi-dependent, non-photosynthetic species, might chemically resemble the fungi it feeds on, reinforcing the adage ‘You are what you eat.’ Thus, the orchid becomes an ideal breeding ground for the fungi-specialized fruit fly. This revelation has profound implications, as it introduces a new category of nursery pollination system, diverging from the genus’ customary deceptive practices.

The researcher adds that this interaction is neither obligatory nor exclusive. The fruit flies also successfully breed on fungi. This discovery, therefore, might signify an evolutionary stepping stone from a deceptive to a mutualistic relationship. Two factors support this claim: the negligible cost to the orchid post-pollination and the prevalent deceptive strategies in closely related Gastrodia species that don’t offer nurseries.

Suetsugu concludes that this research furnishes the inaugural evidence of nursery pollination in orchids, an incredibly diverse plant group comprising almost 30,000 species. It additionally offers valuable insights into the complex, reciprocally advantageous relationships that can evolve in the natural world. These findings could influence broader studies of plant-animal interactions and their evolutionary trajectories.

Reference: “A Novel Nursery Pollination System Between a Mycoheterotrophic Orchid and Mushroom-Feeding Flies” by Kenji Suetsugu, published on 23 August 2023 in Ecology.
DOI: 10.1002/ecy.4152

Financial support for this research was provided by the Japan Science and Technology Agency.

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More about Nursery Pollination in Orchids

• Nursery Pollination in Orchids: A Novel System
• Kobe University Plant Biology Research
• Japan Science and Technology Agency Funding
• Overview of Symbiotic Relationships in Plants
• Ecology Journal
• Plant-Animal Interactions: An Evolutionary Perspective
• Orchids: Diversity and Evolution