Who are the secret gardeners of a parasitic plant?
In the coastal forests of a tropical Japanese island near Okinawa grows an inconspicuous plant that is easy to mistake for a mushroom. It is a non-green parasite that feeds on the roots of other plants and produces up to 1 million tiny seeds, each covered in a minuscule, dry fruit. The seeds, in particular, present a mystery to scientists: How do they get dispersed?
In the tropical forests near Okinawa, Japan, a non-green plant known as Balanophora fungosa grows inconspicuously among the trees. This plant feeds on the roots of other plants and produces up to a million tiny seeds, each enclosed in a small dry fruit. Scientists have long wondered how these seeds are dispersed, as land hermit crabs were observed eating the fruits of the plant. A Kobe University study marks the first time land hermit crabs have been documented as both external and internal seed dispersers.
Kenji Suetsugu, a botanist involved in the study, noted that previous assumptions suggested the fruits simply fall due to gravity and are carried away by wind. However, the humid and windless forest floor makes this unlikely. Suetsugu hypothesized that ants, crickets, and cockroaches could be the dispersers, but when he covered plants with nets allowing only ants, the fruits were no longer picked up.
Time-lapse cameras revealed that land hermit crabs - specifically Coenobita brevimanus - were the primary dispersers. The crabs scraped off the fruits, sometimes removing entire fruit groups overnight, and some seeds even survived passage through the crabs' digestive tract. The crabs' ability to travel up to 100 meters suggests they are effective dispersers.
Suetsugu observed that the crabs actively sought out mature plants, likely attracted by the scent mature plants emit, making them direct advertisements to invertebrates known for feeding on any available ground-level resources. While large vertebrates have been the focus in seed dispersal studies, invertebrates like land hermit crabs often go unnoticed.
Suetsugu believes small-bodied invertebrates play a crucial role in maintaining seed movement, particularly on islands, in fragmented habitats, and on shaded forest floors. His study highlights the unexpected role of land hermit crabs in seed dispersal, with their abundance in coastal forests and omnivorous feeding habits potentially indicating a more general pattern.
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