Possible Spore Dispersal of a Bird-Nest FernAsplenium setoiby Bonin flying foxesPteropus pselaphon

Abstract

Fern spores are generally considered to be dispersed by abiotic processes, particularly anemochory (wind dispersal). Recently, it was shown that Bonin flying foxes Pteropus pselaphon feed on fronds of Asplenium setoi, a species of bird-nest fern, because its spores were found in the flying fox feces (Nakamura et al. 2008). This discovery implied that Bonin flying foxes might serve as biotic agents of Asplenium spore dispersal. However, it is not known whether the spores that pass through the gut of the Bonin flying fox maintain their germinability and viability. Flying foxes Pteropus spp. frequently interact with plants as pollinators and seed dispersers, particularly on isolated oceanic islands (Cox et al. 1991; Elmqvist et al. 1992; Rainey et al. 1995; Nyhagen et al. 2005). Insular flying foxes, members of the genus Pteropus, eat various parts of many plants species, including fruits, flowers, and leaves (Funakoshi et al. 1993; Entwistle and Corp 1997; Banack 1998; Nyhagen et al. 2005; Inaba et al. 2005; Nakamoto et al. 2007). Insular flying foxes appear to have a generalist diet strategy; they consume a taxonomically nonrandom set of plant species and do not focus on the core plant taxa on small oceanic islands with unpredictable fruit resources. In terms of their diet strategy, they can, therefore, be considered as sequential specialists (Banack 1998). Flying foxes squeeze plant pulp and then drink the juice or sap and do not swallow seeds > 5 mm in diameter (Richards 1995). The germination of small seeds (< 5 mm) passed through the gut has been verified in some flying fox species (Entwistle and Corp 1997; Nakamoto et al. 2007). Parsons et al. (2007) reported that bryophyte fragments found in feces of the spectacled flying fox Pteropus conspicillatus, found in Australian tropical forests, grew when cultured, suggesting that flying foxes can play a role as dispersal vectors of mosses. Fern spores are diaspores and are generally considered to be dispersed by wind. If spores in the feces germinate and develop into prothallia, then the flying foxes might be able to disperse the spores. Furthermore, in many ferns, including Asplenium setoi, growth from spores to sporophytes requires sexual reproduction (fertilization) with outbreeding (outcrossing) between two different prothallia (gametophytes). Many ferns have selfincompatibility in the prothallium and cannot perform self-fertilization (selfing) (Soltis and Soltis 1992). Biotic dispersal processes favor ferns with these characteristics, because several spores of the same species tend to be dispersed together. In this study, we used a germination test to examine whether spores of a bird-nest fern retain viability and fertility after their passage through the digestive tract of flying foxes. We performed DNA analysis of the ferns, as it is almost impossible to morphologically distinguish A. setoi from the related species of the genus Asplenium based on the young fronds.