Reproductive biology of rainforest Rutaceae : floral biology, breeding systems and pollination vectors of Acronychia oblongifolia and Sarcomelicope simplicifolia subsp. simplicifolia

The conservation of plant species requires an understanding of the factors that affect viable seed production, but often these factors are poorly understood. We investigated the reproductive biology of two Australian endemic rainforest species, Acronychia oblongifolia (A.Cunn. ex Hook.) Endl. ex Heynh and Sarcomelicope simplicifolia (Endl.) T.G.Hartley subsp. simplicifolia, with the intent of improving conservation and restoration outcomes. The floral biology of these species was quantified to provide baseline data and insights into their pollination syndrome. Flower visitor surveys (using both digital recordings and human observations), a manipulative wind pollination experiment, and hand-pollination experiments were carried out to investigate pollination vectors and determine the breeding system. Acronychia oblongifolia and Sarcomelicope simplicifolia subsp. simplicifolia were both found to best fit the general entomophily pollination syndrome. All floral visitors were arthropod species (Acronychia oblongifolia: 31; Sarcomelicope simplicifolia subsp. simplicifolia: 47) and fewer than 30% of the floral visitors identified, predominantly Diptera, Hymenoptera and Coleoptera, were regarded as potential pollinators. Failure of simulated wind gusts (40 km h-1) to transport pollen 50 cm indicated anemophily is unlikely for these species. Autonomous and manipulative selfing treatments produced few (Acronychia oblongifolia: <3%) or no (Sarcomelicope simplicifolia subsp. simplicifolia) viable seed, indicating these are predominantly outcrossing species, although fruit and viable seed production were highly variable within and among all other treatments (open to natural pollinators, pollinator exclusion, pollinator exclusion and manipulative outcross, and pollinator exclusion and manipulative selfing). Pre-dispersal seed predation was recorded for both species, at several study sites. Pre-dispersal seed predation and increased distances between compatible individuals caused by habitat fragmentation, are two factors limiting the production of viable seeds for both species.