Orchids are known for their intricate and specialized relationships with their pollinators, often relying on a single species of insect to carry their pollen.
But what happens when the pollinator is absent?
A team of researchers from Kobe University in Japan found out that an orchid species on a remote island had to adapt to a different pollinator, resulting in hybridization with another orchid species and loss of its identity.
The bumblebee and the wasp
The researchers were interested in Goodyera henryi, an orchid that grows on mainland Japan and is pollinated exclusively by a specific bumblebee with long mouthparts.
The bumblebee can reach the nectar at the bottom of the orchid's long flower tube, while transferring the pollen from one flower to another.
However, on Kozu Island, a small island about 170 km south of Tokyo, the bumblebee does not exist. How then does Goodyera henryi survive there?
The researchers observed that, on Kozu Island, Goodyera henryi is pollinated by the same scoliid wasp as its closely related orchid Goodyera similis, which also grows on the island.
The wasp has much shorter mouthparts than the bumblebee, so it cannot access the nectar in the long flower tube of Goodyera henryi.
Instead, it bites a hole in the side of the tube and steals the nectar without touching the pollen.
The researchers also noticed that the flower tube of Goodyera henryi was shorter on the island than on the mainland, suggesting that it had evolved to match the wasp's mouthparts.
However, this also meant that it had become more similar to Goodyera similis, which has a short flower tube and is adapted to being pollinated by the wasp.
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The hybridization and the loss
To confirm their suspicions, the researchers conducted a genetic analysis of the orchids from both locations.
They found that Goodyera henryi on Kozu Island had a high level of hybridization with Goodyera similis, indicating that they had interbred and exchanged genes.
This explained why they had similar flower tube lengths and were both pollinated by the same wasp.
However, this also meant that Goodyera henryi on Kozu Island had lost some of its distinctive features and identity as a separate species.
The researchers speculated that this might have been a trade-off for surviving in an environment where its original pollinator was absent.
By adapting to a new pollinator, it had gained access to nectar and pollen, but at the cost of being hybridized with another species.
The researchers concluded that this case study illustrates how plants in ecological relationships adapt to changing circumstances, and how remote islands can be natural laboratories for studying evolutionary processes.
They also suggested that more studies are needed to understand the long-term consequences of such adaptations for plant diversity and conservation.
The study was published in the journal New Phytologist The lead author was Professor Suetsugu Kenji from Kobe University's Graduate School of Science.
He said: "The combination of our expertise, access to the location, and our interdisciplinary methodology puts us in a special position to study the impact of bumblebee absence on orchid evolution in this context."
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