ORIGINAL ARTICLE Andromonoecy and high fruit abortion in Anthonotha noldeae in a West African montane forest Merodie A. Beavon • Hazel M. Chapman Received: 16 November 2010 / Accepted: 4 June 2011 / Published online: 30 June 2011 Ó Springer-Verlag 2011 Abstract Anthonotha noldeae (Rossberg) Exell et Hillc. Leguminosae, Caesalpinioideae, an Afromontane forest canopy tree, produces a superabundance of flowers, but few (1.1%) initiate fruits, and even fewer (0.44%) reach maturity and disperse. Fifty-three percent of fruits are predated. A. noldeae is andromonoecious. Over all 20 trees for which we counted floral gender ratios (hermaphrodite vs. staminate flowers), the ratio was 2.1:1. There was sig- nificant (F 19,379 = 8.52; p \ 0.001) variation in the pro- portion of the two flower types produced among individuals. Floral gender ratios did not predict the pro- portion of mature fruits produced on a tree (r 2 = 0.066; p = 0.273), or its phenotypic gender (Gi)—which is defined as the contribution of an individual tree to the next generation in terms of female function relative to all other individuals in the population (r 2 = 0.069; p = 0.262). Gi varied among trees from 0 (functionally male) to 0.8. There was no correlation between tree size and phenotypic gender (r = 0.08; p = 0.74; n = 20). Open flowers initi- ated significantly more fruits than bagged or caged flowers (p = 0.0073), showing A. noldeae relies on birds to pro- duce fruits. However, 80% of visits to flowers were made by insects, while only 20% of visits were from pollinating sunbirds. While low fruit initiation was the most restrictive reproductive step, low pollination rates combined with insect robbers, fungal attacks and high levels of predation of immature fruits may contribute to the extremely low fruit set in A. noldeae. Keywords Plant gender Á Andromonoecy Á Breeding systems Á Afromontane forests Á Fruit abortion Introduction Many plant species produce a superabundance of flowers and immature fruits (Bawa and Webb 1984; Lloyd 1980a; Stephenson 1981). High abortion rates of flowers and fruits are common, and in extreme cases less than one percent of flowers develop into mature fruits (Bawa and Webb 1984; Lewis and Gibbs 1999). Unpredictability in terms of flower predators, pathogens, pollinators and weather conditions could all theoretically select for an excess of flowers (Burd 1998; Ehrlen 1991; Stephenson 1981; Bawa and Webb 1984). There are many hypotheses used to explain a superabundance of flowers. Some suggest it increases plant fitness through male function. For example, sexual selec- tion theory (Bawa and Webb 1984; Janzen 1977; Lloyd 1980a; Sutherland and Delph 1984) assumes aborted flowers are functionally male (aborting before fertilisation if hermaphrodite), so their presence increases individual male reproductive success by providing more pollen with which to compete for the fertilisation of ovules. In contrast, the pollen limitation hypothesis (Bierzychudek 1981; Burd 1994; Janzen 1977) proposes that when pollinators are scarce, an increased floral display is more likely to attract pollinators, increasing the likelihood of producing out- crossed progeny, thus improving female function [but see Bawa and Webb (1984)]. Similarly, the genotype sorting hypothesis (Bawa and Webb 1984; Marshall and Ellstrand 1988; Stephenson 1981) is based on the surmise that excess M. A. Beavon Á H. M. Chapman (&) School of Biological Sciences, University of Canterbury, PB 4800 Christchurch, New Zealand e-mail: hazel.chapman@canterbury.ac.nz 123 Plant Syst Evol (2011) 296:217–224 DOI 10.1007/s00606-011-0488-1