JOBNAME: No Job Name PAGE: 1 SESS: 8 OUTPUT: Fri Feb 11 14:58:11 2011 SUM: 9C3E0E53 /v2451/blackwell/journals/psbi_v0_i0/psbi_320 Phenotypic selection on flowering phenology and size in two dioecious plant species with different pollen vectors MIGUEL A. MUNGUIA-ROSAS,*† JEFF OLLERTON* and VICTOR PARRA-TABLA† *School of Science and Technology, Avenue Campus, University of Northampton, Northampton, NN2 6JD, UK and †Tropical Ecology Department, Biological and Agronomic Science Campus, Yucatan University, AP 4-116, Col. Itzimná, 97100, Merida, Yucatan, Mexico Abstract Dioecious plants may be pollinated biotically by animals or abiotically via wind or water currents. It has been hypothesized that these two types of pollen vectors might impose contrasting selective pressures on plant flowering phenology. In the present study we describe the flowering phenology of two sympatric dioecious species with contrasting pollination modes: Mercurialis perennis (wind-pollinated) and Tamus communis (insect- pollinated). We estimated selection differentials and gradients for flowering time and flowering synchrony. As flowering time might depend on the accumulation of enough internal resources, we also estimated direct and indirect selection on plant size. Both species have male-biased sexual ratios, and males are bigger and produce larger flower displays than females, but only in T. communis do males bloom earlier and for longer than females. Selection gradients suggest that selection tends to favor early-flowering females of T. communis. There is no evidence of direct current selection on the flowering phenology of M. perennis. Intersexual differences in phenology fit with sex allocation and sexual selection theories. As we hypothesized, phenology of the animal-pollinated species is under stronger selection than that of the wind-pollinated species and we discuss the potential role of pollen vectors in shaping the flowering phenologies of the study species. Keywords: dioecy, flowering phenology, mutualism, phenotypic selection, wind pollination. Received 12 August 2010; accepted 4 December 2010 Introduction Dioecy is a plant sexual system where all genets in a population are either male or female (Richards 1986). This sexual system is relatively rare among angiosperms; it occurs in only approximately 6% of species (Renner & Ricklefs 1995) and evolved either directly from hermaph- roditism or indirectly via gynodioecy, androdioecy or monoecy (Bawa 1980).Although it is widely accepted that the evolution of dioecy resulted from selective pressures promoting out-crossing, other ecological factors such as resource availability, sexual selection and pollination vectors are also important (Bawa 1980; Ashman 2006). These ecological factors can also interact and together result in the evolution of separate sexes; for example, resource-mediated changes in plant phenotype can alter the degree of pollination and pollinator movements, and thus ultimately the sexual system (Ashman 2006). There exist some interesting correlations between dioecy and life-history traits. Dioecious plants are typically perenni- als, have fleshy fruit and small inconspicuous flowers, and are pollinated either by insects or wind (Bawa 1980; Renner & Ricklefs 1995; Vamosi et al. 2003). Dioecious plants are frequently highly generalist (e.g. Matsuyama et al. 2009), although they may be more specialized (with fewer insect pollinators) in the tropics (Renner & Feil 1993). In flowering plants as a whole, wind pollination evolved from insect-pollinated plants, very probably as a reproductive assurance strategy (Culley et al. 2002), although it is still relatively rare compared with animal pollination (Ollerton et al. in press). Wind pollination has evolved more frequently in dioecious plants because Correspondence: Miguel A. Munguía-Rosas Email: allusion82@hotmail.com Plant Species Biology (2011) ••, ••–•• doi: 10.1111/j.1442-1984.2011.00320.x © 2011 The Authors Journal compilation © 2011 The Society for the Study of Species Biology 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64