Social wasps, crickets and cockroaches contribute to pollination of the holoparasitic plant Mitrastemon yamamotoi (Mitrastemonaceae) in southern Japan

Abstract

Mitrastemon yamamotoi is completely embedded within the tissues of its hosts, except during the reproductive stage, when aboveground parts emerge from host tissues. Its highly modified appearance has attracted attention of many botanists, but very little is known about the reproductive system. Floral visitors to M. yamamotoi were observed in southern Japan. Pollination experiments were conducted to determine the plant's self-compatibility and pollen limitation, as well as the contribution of diurnal and nocturnal visitors to fruit set and outcrossing. Mitrastemon yamamotoi is mainly pollinated by social wasps, but previously unnoticed pollinators (i.e. crickets and cockroaches) are also important, based on visitation frequency and pollen loads. Results of the pollination experiments suggest that nocturnal visitors, such as crickets and cockroaches, contribute to geitonogamous pollination, whereas diurnal visitors, such as social wasps, facilitate outcrossing. The unexpected pollinator assemblage of M. yamamotoi might be influenced by multiple factors, including the highly modified flowers that are produced close to the ground in dark understorey environments, the species' winter-flowering habit and the location of the study site (i.e. near the northern limit of the species' range). Considering that M. yamamotoi occurs widely in subtropical and tropical forests in Asia, additional studies are needed to assess pollinator assemblages of M. yamamotoi at other locations.

Oxygyne: An extraordinarily elusive flower

“…Given that T. hongkongensis shares morphological features with Oxygyne (perianth tubes with an annulus and tepal extensions), a similar pollination syndrome is possible for Oxygyne. Meanwhile, Mitrastemon yamamotoi (Mitrastemonaceae) , a holoparasitic species (a parasite devoid of chlorophyll) which also produces flowers close to the ground in dark understorey environments, was recently established to be pollinated by social wasps, crickets, and cockroaches (Suetsugu, ). Suetsugu () suggests that pollination systems involving unusual and unexpected taxa might be more widespread than previously thought, especially in non‐photosynthetic plants with highly modified floral morphology.…”

“…Meanwhile, Mitrastemon yamamotoi (Mitrastemonaceae) , a holoparasitic species (a parasite devoid of chlorophyll) which also produces flowers close to the ground in dark understorey environments, was recently established to be pollinated by social wasps, crickets, and cockroaches (Suetsugu, ). Suetsugu () suggests that pollination systems involving unusual and unexpected taxa might be more widespread than previously thought, especially in non‐photosynthetic plants with highly modified floral morphology. These recent studies show that investigation into the pollination syndrome of the genus Oxygyne warrants much further attention.…”

Fruit‐ and seed‐feeding habit of the crane fly Libnotes puella (Diptera: Limoniidae) in Ryukyu Islands, Japan

“…We also identified two limonid flies (1♂ and 1♀) that visited the inflorescences of M . yamamotoi , reported by Suetsugu (), as L . puella .…”

“…puella oviposited on M . yamamotoi in the flowering season (Suetsugu ); the larvae fed only on the placenta of the infructescences without exploiting their seeds, and the adults emerged from the infructescences (Fig. ).…”

“…Consequently, no pollen grains were found attached to L . puella bodies (Suetsugu ). Therefore, the relationship between Libnotes and Mitrastemon probably does not involve brood‐site pollination mutualism, but the possibility deserves further investigation.…”