Sexual Conflict Over Floral Receptivity

Abstract

Abstract. In flowering plants, the onset and duration of female receptivity vary among species. In several species the receptive structures wilt upon pollination. Here we explore the hypothesis that postpollination wilting may be influenced by pollen and serve as a general means to secure paternity of the pollen donor at the expense of female fitness. Taking a game-theoretical approach, we examine the potential for the evolution of a pollen-borne wilting substance, and for the coevolution of a defense strategy by the recipient plant. The model without defense predicts an evolutionarily stable strategy (ESS) for the production of wilting substance. The ESS value is highest when pollinator visiting rates are intermediate and when the probability that pollen from several donors arrives at the same time is low. This finding has general implications in that it shows that male traits to secure paternity also can evolve in species, such as plants, where mating is not strictly sequential. We further model coevolution of the wilting substance with the timing of stigma receptivity. We assume that pollen-receiving plants can reduce the costs induced by toxic pollen by delaying the onset of stigmatic receptivity. The model predicts a joint ESS, but no female counter-adaptation when the wilting substance is highly toxic. This indicates that toxicity affects the probability that a male manipulative trait stays beneficial (i.e., not countered by female defense) over evolutionary time. We discuss parallels to male induced changes in female receptivity known to occur in animals and the role of harm for the evolution of male manipulative adaptations.Key words. Arms race, floral longevity, pollen competition, pollination, protandry, receptivity.Over all reproductive modules, the female function of many plant species is often pollen limited . Nevertheless, in animal-pollinated plants, pollen deposited on single flowers often exceeds the number of fertilizable ovules (Levin 1990;Bernasconi et al. 2006a) and is derived from genetically different pollen donors (Ellstrand 1984;Marshall and Ellstrand 1985;Campbell 1998; S. Teixeira and G. Bernasconi, unpubl. ms.), providing opportunity for competition among different pollen donors for fathering the seeds (Delph and Havens 1988;Snow and Lewis 1993;Stanton 1994;Bernasconi 2003).The length of time a flower is open and the duration of receptivity of female function beyond the first pollen deposition may influence the number of effective pollinator visits and thus reproductive success. Specifically, variation in floral longevity may affect the number and genetic diversity of competing pollen donors (Primack 1985;Galen et al. 1986;Bingham and Orthner 1998;Ashman 2004) and yield a range of benefits to the pollen recipient. These include ensuring sufficient pollen; optimizing genetic composition of the pollen load; increasing the probability of outcrossing; and increasing number, genetic diversity or quality of the offspring (Schemske and Pautler 1984;Schlichting et al. 1987Schlichting et al. ...

Using theories of sexual selection and sexual conflict to improve our understanding of plant ecology and evolution

“…1) (Bernasconi et al 2004), for example over floral receptivity, where selection will favour harmful pollen with an ability to fertilize the ovules ahead of others, securing paternity at the expense of female fitness (Lankinen et al 2006). It is known that pollen deposition can induce floral changes, e.g.…”

“…It is also noteworthy that development of sexual selection theory into the theory of sexual conflict (Parker 1979; Chapman et al 2003), which is widely investigated in insects, was only considered relatively recently in plants (Bernasconi et al 2004; Lankinen et al 2006; Prasad and Bedhomme 2006; Delph and Herlihy 2012). In Web of Science, the search term ‘sexual conflict plant*’ and ‘sexual conflict animal*’ finds 280 and 3311 articles, respectively, during the last 10 years (2004–14) thus around 12 times more studies made on animals (please note that this was an equally rough survey as above).…”

Conflicting selection pressures on reproductive functions and speciation in plants

“…Most of these approaches are applicable to plants, but of course we also need to carefully consider differences between taxa when constructing experiments, such as the dependence of pollinators in many plants (cf. Lankinen et al 2006).…”

“…It has recently been suggested that parental conflicts in plants can also be expressed during pollen competition (Brandvain and Haig 2005;Lankinen et al 2006). In angiosperms, closed carpels and transfer of male gametes from the stigma to the ovules via a pollen tube (siphonogamy) separate pollen arrival on the stigma from conception, creating an arena for pollen competition and female choice after pollen transfer (Mulcahy 1979;Skogsmyr and Lankinen 2002).…”

“…Floral longevities have, however, also been found to be shorter than Evol Ecol (2009) 23:147-157 149 expected by this trade-off (Schoen and Ashman 1995). In a recent model, Lankinen et al (2006) showed that a pollen trait that induces floral wilting can evolve because this will secure paternity by preventing arrival of pollen from other donors. Thus, the pollen trait manipulates the female function by influencing pollinator access to the flower (possibly by exploiting an existing mechanism).…”