The finding of an unusual instance where the same insect species is responsible for both pollinating a plant and spreading its seeds not only unravels an age-old botanical enigma but also highlights the various functions insects serve in our ecosystems.
The discovery of an unusual instance where the same insect species is responsible for both pollinating a plant and spreading its seeds not only unravels an age-old botanical enigma but also highlights the various functions insects serve in our ecosystems.
In the damp and shadowy understory of the subtropical forests located on Shimoshima Island in Japan, there thrive parasitic plants known as Balanophora, which derive their nutrients from the roots of other plants. For over a century, the method by which these plants disperse their seeds has remained unclear. While it was proposed that their minuscule seeds are blown away by the wind, the reality is that there is minimal wind in these (sub)tropical forest understories. Some varieties of Balanophora feature vibrant red colors, akin to strawberries, which attract birds and rabbits that help in seed dispersal. However, others, like Balanophora subcupularis, are dull in appearance and emit a yeasty scent, reducing the likelihood of involvement from vertebrates. The means by which these plants are pollinated has also been a mystery.
SUETSUGU Kenji, a botanist at Kobe University with a focus on the relationships between these parasitic plants and their ecosystems, emphasizes the often overlooked yet vital contributions of invertebrate pollinators and seed dispersers. To explore which creatures help B. subcupularis in its reproductive process, he and his team monitored the plants for over 100 hours and captured tens of thousands of automated nighttime images while the flowers were in bloom or when they bore fruit, identifying the insects that visited. Additionally, they conducted experiments to exclude animals and to observe seed feeding, confirming whether the insects they recorded are indeed effective pollinators and seed dispersers.
In two consecutive papers published in the journal Ecology, the team reported that B. subcupularis is pollinated by ants and camel crickets, which are drawn to the plants for their pollen and nectar. Interestingly, these same insects also consume the fleshy leaves that contain the seeds, thereby assisting in seed dispersal. “While it’s well-acknowledged that many plants depend on insects for pollination, it’s uncommon for ants and crickets to perform this function. Additionally, many plants utilize birds and mammals for fruit distribution, making it particularly rare for crickets or other small arthropods to take on this role. What is even more remarkable is that the same animal fulfills both roles, which is an exceptional occurrence,” remarked Suetsugu, expressing his astonishment at this discovery.
Suetsugu proposes that this rare dual function of pollination and seed dispersal may be shaped by two factors. First, he notes that “B. subcupularis flowers late in the year when most typical pollinators, such as bees, are less active. Furthermore, our research area is a small island at the northern limit of the plant’s habitat, possibly contributing to the reduced presence of pollinators and seed dispersers.”
The broader implications of these findings are not lost on Suetsugu: “This highlights the critical role invertebrates play in plant reproduction and prompts further exploration into how these relationships have evolved and what environmental influences foster such extraordinary adaptations. From a practical standpoint, our findings aid conservation strategies for rare and endangered species like Balanophora subcupularis. By understanding their dependence on specific invertebrates for both pollination and seed dispersal, we can better inform efforts in habitat preservation and the management of invertebrate populations, which are essential for these plants’ survival.”
This research was funded by the Japan Science and Technology Agency (grant JPMJPR21D6).