Reproductive biology of the threatened and highly fragmented shrub

Abstract

The Australian Proteaceous genus Persoonia is known to be pollinated by bees and have variable breeding systems that range from strictly self-incompatible to differing levels of self-compatibility. The endangered Persoonia hirsuta (Hairy Geebung) is a species currently in decline throughout its distribution, with many populations occurring in fragmented habitats comprising fewer than 10 plants or a single isolated individual. Despite its threatened status and recent population decline, the reproductive biology of P. hirsuta is unknown. In this study, we surveyed floral visitors and their foraging behaviour, and investigated the breeding system of P. hirsuta by conducting experimental hand-pollinations at two of the largest known populations. P. hirsuta was almost exclusively visited by native bees, including Leioproctus, Megachile and Tetragonula species. This study was the first to report Xylocopa bees and Zizinia butterflies visiting Persoonia flowers. On average, both foraging time per flower and the number of flowers visited per plant varied significantly among insect genera. Notably, Xylocopa bees visited more flowers per plant than did any other pollinator (22.1 ± 10.8 flowers). P. hirsuta has a breeding system that displays partial self-incompatibility with significantly higher fruit set in the cross- and open-pollination treatments at both populations (19.4 ± 10.8 to 44.8 ± 8.2%) than in the autogamy and selfed treatments (0.6 ± 0.6 to 9.0 ± 5.1%). The results of this study are critical to the future management of P. hirsuta, and suggest that its small and isolated populations may produce very few viable fruits in the absence of outcrossing.