Contrasting breeding systems revealed in the rainforest genus Davidsonia (Cunoniaceae): can polyembryony turn the tables on rarity?

Abstract

Plant breeding systems can have a profound effect on a species ability to persist, colonise new areas and adapt to environmental change. Determining the breeding systems in rare and common congeners may shed light on factors influencing rarity. Endemic to Australia, the Davidsonia genus comprises three species of rainforest trees. The two sympatric, subtropical species, Davidsonia jerseyana (F.Muell. ex F.M.Bailey) G.Harden & J.B.Williams, and D. johnsonii G.Harden & J.B.Williams, are endangered whereas the tropical D. pruriens F.Muell. is widespread. Other than exclusive clonality in D. johnsonii, the reproductive systems in the genus are unknown. We used segregation analysis of microsatellite loci in open-pollinated progeny arrays to investigate the breeding systems in D. jerseyana and D. pruriens. Reproductive success, under glasshouse conditions, was measured by the proportion of viable seeds, germination rate and seedling growth and survival over 12 months. Davidsonia jerseyana appears to be predominantly selfing with high fecundity. In D. pruriens, polyembryony was common and 89% of the progeny were identical to the heterozygous maternal parent, implying likely apomixis. Overall, fecundity was significantly lower than for D. jerseyana, although survival was higher from D. pruriens polyembryonic than from monoembryonic seed. The high fecundity in D. jerseyana indicates a lack of inbreeding depression and also suggests that it would be less likely to be endangered than the less fecund D. pruriens. This raises the possibility that polyembryony and likely apomixis may provide a reproductive advantage to D. pruriens, which could otherwise share rarity with its congeners.