Pollinators’ mating rendezvous and the evolution of floral advertisement Michael A. Fishman, Lilach Hadany n Department of Molecular Biology and Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel HIGHLIGHTS c Allocation of plant resources to attracting vs. rewarding pollinators has an optimum. c This optimum is attainable through a sequence of small variation/selection steps. c Plants where pollinators also mate should advertise more and reward less. c The results can be tested by examination of plant/pollinator populations. article info Article history: Received 17 April 2012 Received in revised form 29 August 2012 Accepted 6 September 2012 Available online 27 September 2012 Keywords: Resource allocation Floral advertisement Alternate rewards Plant pollinator coevolution Resource defense polygyny abstract Successful cross-fertilization in plant species that rely on animal pollinators depends not just on the number of pollinator visits, but also on these visits’ duration. Furthermore, in non-deceptive pollination, a visit’s duration depends on the magnitude of the reward provided to the pollinator. Accordingly, plants that rely on biotic pollination have to partition their investment in cross- fertilization assurance between attracting pollinator visits – advertisement, and rewarding visitors to assure that the visit is of productive duration. Here we analyze these processes by a combination of optimality methods and game theoretical modeling. Our results indicate that the optimality in such allocation of resources depends on the types of reward offered to the pollinators. More precisely, we show that plants that offer both food reward and mating rendezvous to pollinators will evolve to allocate a higher proportion of their cross-fertilization assurance budget to advertisement than plants that offer only food reward. That is, our results indicate that pollinators’ mating habits may play a role in floral evolution. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction A flowering plant has to allocate finite resources to many diverse functions. Evolutionary success accrues to genotypes that optimize resource allocation to growth/survival vs. reproduction – either sexual or asexual. Finally, the investment in sexual reproduction involves partitioning of resources between cross- fertilization assurance and seed/fruit production (cf. Charlesworth and Morgan, 1991). In plants that rely on biotic pollination, the investment in assuring cross-pollination has two main components: attracting pollinator visits – advertisement; and rewarding visiting pollina- tors because successful pollen transfer depends on a visit’s duration (Jones and Reithel, 2001), which increases with the magnitude of the reward (Chittka et al., 1997; Howell and Alarcon, 2007). Let us define advertisement as any signals produced by a flowering plant that increase the probability of a visit by a pollinator (cf. Fenster et al., 2006; Raguso et al., 2007). That is, plant’s signals that constitute its appeal to pollinators. There are several types of plant signals attracting pollinators e.g., flower or inflorescence shapes (M¨ oller and Sorci, 1998; Wignall, 2006; Whitney and Glover, 2007), color schemes (Wilbert et al., 1997; Wesselingh and Arnold, 2000; Johnson and Midgley, 2001), flower or inflorescence size (Spaethe et al., 2001; Davis et al., 2008), and floral scents (Knudsen et al., 2001; Raguso, 2008). Not all floral attributes are equally well suited for advertisement. For example: small changes in flower shape and/or color can cause major differences in the perception of that plant by its pollinators (Chittka, 1997; Dyer et al., 2007) – a change what may render the plant unattractive to them (Wesselingh and Arnold, 2000). Here, we focus on the variation in quantitative floral signals, such as floral/ inflorescence size or the intensity of scent. There are two confounding aspects when dealing with this subject. On one hand, in many cases a pollinator cannot detect, barring direct comparison, small differences in the magnitude of quantitative signals. Thus, the only effect of an increased signal magnitude Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/yjtbi Journal of Theoretical Biology 0022-5193/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jtbi.2012.09.006 n Corresponding author. Tel.: þ972 364 09831. E-mail addresses: lhadany@post.tau.ac.il, lilach.hadany@gmail.com (L. Hadany). Journal of Theoretical Biology 316 (2013) 99–106