Original article Reproductive consequences of mate quantity versus mate diversity in a wind-pollinated plant K. Vandepitte a, b, * , I. Rolda ´ n-Ruiz b , O. Honnay a a Laboratory of Plant Ecology, University of Leuven, Arenbergpark 31, 3001 Heverlee, Belgium b Plant – Growth and Development, Institute for Agricultural and Fisheries Research, Caritasstraat 21, 9090 Melle, Belgium article info Article history: Received 7 February 2009 Accepted 24 April 2009 Published online 17 May 2009 Keywords: Wind-pollinated Dioecious AFLP Mate availability Mate diversity Mate proximity Pollen limitation Mercurialis perennis abstract Since most pollen travels limited distances in wind-pollinated plants, both the local quantity and diversity of mates may limit female reproductive success. Yet little evidence exists on their relative contribution, despite the importance of viable seed production to population dynamics. To study how variation in female reproductive success is affected by the quantity versus the diversity of surrounding mates contributing pollen, we integrated pollination experiments, data on natural seed set and seed viability, and AFLP genetic marker data in the wind-pollinated dioecious clonal forest herb Mercurialis perennis. Pollination experiments indicated weak quantitative pollen limitation effects on seed set. Among- population crosses showed reduced seed viability, suggesting outbreeding depression due to genetic divergence. Pollination with pollen from a single source did not negatively affect reproductive success. These findings were consistent with results of the survey of natural female reproductive success. Seed set decreased with the distance to males in a female plants’ local neighborhood, suggesting a shortage of pollen in isolated female plants, and increased with the degree of local genetic diversity. Spatial isolation to other populations and population size did not affect seed set. None of these variables were related to seed viability. We conclude that pollen movement in M. perennis is likely very limited. Both male proximity and the local degree of genetic diversity influenced female reproductive success. Ó 2009 Elsevier Masson SAS. All rights reserved. As plants often mate and disperse offspring locally, one impor- tant question in plant reproductive ecology is to what extent female reproductive success in outcrossing plants is affected by surrounding mates contributing pollen. Increased reproductive success after manual pollinations is commonly attributed to insufficient pollen due to a shortage of mates or pollinators in natural conditions (reviewed in Burd, 1994; Ashman et al., 2004). In contrast, recent evolutionary models predict that seed output should at evolutionary equilibrium never be limited by the quantity of pollen (Harder and Routley, 2006; Harder et al., 2008). The widespread observation of pollen-limited reproduction in angiosperms could, therefore, represent the effects of poor pollen quality rather than insufficient pollen (Harder et al., 2008). Indeed, genetic studies support the idea that low mate diversity can negatively affect reproduction through poor pollen quality. A low number of different mates can reduce seed set and viability due to reduced pollen competition or selection (Marshall and Ellstrand, 1986; Winsor et al., 2000; Paschke et al., 2002), while a declining genetic diversity among mates, for instance due to mating among relatives, can increase seed and embryo abortion through the accumulation of deleterious alleles (Charles- worth, 1989; Waser and Price, 1989; Keller and Waller, 2002). However, available studies so far (reviewed in Ashman et al., 2004 and Ghazoul, 2005) rarely weighed the influence of the diversity versus the quantity of mates (but see Campbell and Husband, 2007). This is certainly true for wind-pollinated plants where pollen- limited reproduction was recognized only recently (Knapp et al., 2001; Davis et al., 2004). Wind-dispersed pollen typically shows a leptokurtic dispersal curve from static point sources with most pollen deposited near the source and a long flat tail characterized by low deposition (Levin and Kerster, 1974; Tonsor, 1985). Therefore, the proportion of fertilized ovules can rapidly decrease with the distance to, and local number of mates, in outcrossing wind-pollinators (Allison, 1990; Knapp et al., 2001; Davis et al., 2004; Steven and Waller, 2007; Stehlik et al., 2008). Yet, as most pollen is deposited near the source, female reproductive success of wind-pollinated plants might also * Corresponding author. Laboratory of Plant Ecology, University of Leuven, Arenbergpark 31, B-3001 Heverlee, Belgium. Tel.: þ32 9 2722970; fax: þ32 9 2722901. E-mail address: katrien.vandepitte@bio.kuleuven.be (K. Vandepitte). Contents lists available at ScienceDirect Acta Oecologica journal homepage: www.elsevier.com/locate/actoec 1146-609X/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.actao.2009.04.004 Acta Oecologica 35 (2009) 548–553