Near extinct Argyreia versicolor and rare Argyreia mekongensis are dependent on carpenter bee pollinators

Abstract

Argyreia versicolor and Argyreia mekongensis are extremely rare plant species. The former had not been seen for nearly 100 years until two individuals were found in Thailand in 2018, and only a handful of populations are known for the latter. The aims of this study were to examine the breeding systems of A. versicolor and A. mekongensis using pollination experiments and to determine their potential pollinators via floral observations. Our controlled pollination experiments uncovered the self-incompatibility of both species. Pollinator censuses indicated that females of two carpenter bee species, Xylocopa aestuans and Xylocopa latipes, were the predominant floral visitors for both Argyreia species. Our observations confirmed a harmonious match between the floral shape of both Argyreia species and the body sizes of these pollinators, ensuring effective pollen transfer and validating their role as putative pollinators. In line with the high frequency of pollinator visits observed, our controlled pollination experiments found no evidence of pollen limitation under field conditions. The findings of this study hold significance for the conservation of these endangered species, yet the situation is dire for A. versicolor, with one of the two individuals under study recently lost. Hence, it is crucial to intensify monitoring efforts for the species, aiming to identify additional individuals for potential inclusion in an ex-situ conservation program. Simultaneously, safeguarding the habitat of these plant species and their pollinators will be critical.

Abstract

Argyreia versicolor and Argyreia mekongensis , two species of morning glory endemic to Thailand and neighbouring countries, are extremely rare and knowledge of their reproductive ecology is essential for conservation efforts. Our research found that both species are self-incompatible and require pollinators to reproduce. We also found that both morning glory species are pollinated by carpenter bees ( Xylocopa aestuans and Xylocopa latipes ). Given the extreme rarity of these species (particularly A. versicolor , for which we know of only a single surviving individual), immediate action is needed. Successful conservation will require identifying additional individuals and safeguarding the habitat of these plant species and their pollinators.