Beetle Pollination in the Holoparasitic Lophophytum pyramidale (Balanophoraceae): A New Case of Brood‐Pollination Mutualism?

Beetle pollination is considered an ancestral trait in angiosperms, retained in a few specialised families engaging in longstanding interactions with ancient groups of beetles. While beetles represent some of the earliest angiosperm pollinators, there is also increasing evidence that some beetle‐pollinated plants represent a derived condition. Characterising and describing these interactions is critical to understanding the evolution of beetle pollination and specialised brood pollination (i.e., pollinators that also breed on host plants). Here we focus on the holoparasitic plant Lophophytum pyramidale (Balanophoraceae). This family is one of the most intriguing groups of terrestrial plants characterised by extreme reproductive and vegetative morphology modifications. Still, little is known about most species' reproductive biology and ecological interactions. We investigated the flowering events and floral visitors of a population of L. pyramidale in the Atlantic Rainforest in Brazil. The flowering season lasts about 2 months, and plants are monoecious. Female flowers mature before the male ones, suggesting L. pyramidale is a protogynous species. Three arthropod orders (Coleoptera, Diptera, Hymenoptera) were observed visiting the flowers of L. pyramidale . Beetles, including Oxycorynus melanocerus , O xycorynus nigripes (Belidae: Oxycorynini), Mystrops sp. (Nitidulidae: Mystropini) and other small species of Nitidulidae, Hydrophilidae and Tenebrionidae were commonly observed visiting both male and female flowers and, therefore, are considered the main pollinators. The presence of larvae of Oxycorynini and Nitidulidae beetles developing within the reproductive structures evidences that some pollinators use this plant species as a breeding site, specifically Oxycorynus spp. and the Nitidulidae. Using DNA barcoding, we find further that the two species of Oxycorynus do not have niche partitioning and essentially share the same breeding sites within plants. Overall, we demonstrate that this Balanophoraceae species represents a case of brood‐site pollination by beetles, a condition likely derived within the family.