© CSIRO 2004 10.1071/BT03139 0067-1924/04/020185 www.publish.csiro.au/journals/ajb Australian Journal of Botany , 2004, 52, 185–193 CSIRO PUBLISHING High self-pollen transfer and low fruit set in buzz-pollinated Dianella revoluta (Phormiaceae) David H. Duncan A , Adrienne B. Nicotra A and Saul A. Cunningham B,C A Botany & Zoology, Australian National University, Canberra, ACT 0200, Australia. B CSIRO Entomology, GPO Box 1700, Canberra, ACT 2601, Australia. C Corresponding author; email: saul.cunningham@csiro.au Abstract. We used pollinator observation, flower manipulation, controlled pollination and pollen-tube analysis to better understand the reproductive ecology of Dianella revoluta R.Br., a common species known to have depressed fruit set at fragmented sites. This buzz-pollinated species was found to receive large quantities of self-pollen even during a single pollinator visit, but is only partially self-compatible. This may be the first direct demonstration of pollinator-facilitated, autogamous self-pollen transfer accounting for a significant proportion of stigmatic pollen load. Frequent high self-pollen transfer may account for the observed low rate of fruit development in open-pollinated flowers. Self-pollen tubes reached the base of the style in comparable numbers and at the same rate as outcross pollen tubes, with no sign of pollen-tube competition favouring outcross pollen. Barriers to greater self-fertility occur late, probably through early abortion of selfed ovules. We also investigated what impact overlapping distribution with D. longifolia may have on D. revoluta pollination and reproduction. Although these species shared pollinators, they differed in terms of frequency of visits. There was also separation of floral phenology within the course of a day. BT03139 Poli nationandm atings ystemof D.revoluta D.H.Duncan etal . Introduction Although many factors influence the susceptibility of plant species to habitat-fragmentation effects, there is agreement that pollination specialisation, and mating system, are likely to be important determinants of a species’ level of risk (Bond 1994; Murcia 1996). Native-pollinator faunas have been shown to decline in fragmented landscapes (Aizen and Feinsinger 2002) and, all else being equal, species with fewer potential pollinators have a higher probability of losing theirs during this process of attrition (Bond 1994). Species that are self-incompatible are also likely to suffer reproductive declines because of greater dependence on adequate pollinator service for outcross-pollen receipt. Net reproductive success of plants, however, also depends on many other aspects of a species’ biology and life history, and the interplay between those traits. Indeed, a recent meta-analysis by Aizen et al. (2002) found that species’ self-incompatibility and degree of pollinator specialisation were not good predictors of fragmentation effects, at least not as they are usually assessed. For many plant species we will need to know more about pollinator behaviour and the pollen-flow dynamics that occur when pollinators visit, in order to gauge the importance of pollination biology and mating system. For example, ongoing reproductive success may be relatively secure for a self-incompatible species if it is well supplied with outcross pollen. Alternatively, a generalist-pollinated species may be prone to suffer reproductive failure because of being swamped by pollen from other plant species. Ideally, a species’ pollinator service should be determined from field studies that consider the outcome of pollinator behaviour at flowers (e.g. Snow 1982) as well as season-to-season variation in pollinator distribution and abundance (e.g. Minckley et al. 1999). High-resolution studies on single species are a key part of developing our understanding of fragmentation effects (Aizen and Feinsinger 2002). In this study, we investigated the reproductive ecology of D. revoluta—a common and sometimes dominant understorey species of mainland Australia, where it often forms large clonal patches (Henderson 1987). Despite its considerable distribution and abundance, a study of fragmentation effects in mallee woodland found that fruit-set efficiency of D. revoluta was significantly higher in nature reserves than in nearby linear strips (Cunningham 2000). One of the key concerns relating to habitat fragmentation is that effects may take the form of a slow erosion of essential