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. ...

Enhanced frugivory on invasive Silene latifolia in its native range due to increased oviposition

“…Greater risk of oviposition in North American plants might arise if flowers on North American plants were open and attractive for a longer time than on European plants. Because S. latifolia flowers wilt rapidly after pollination (Lankinen et al. 2006), if North American plants experienced lower pollinator visitation they might remain open for longer, thereby increasing the time of exposure of individual flowers.…”

Intrafloral phenology of Trifolium polymorphum Poir. (Leguminosae) aerial flowers and reproductive implications

“…This recorded period was obtained in cultivated experimental conditions (without environmental factor control) in which the pollination effect was not considered. Pollination usually reduces floral longevity by means of ethylene production (Stead 1992;Proctor & Harder 1995;van Doorn 1997;Arathi et al 2002), and it is a way to minimize the invested female resources and assure male fitness by reducing pollen-grain competition once the grains reach the stigmatic surface (Lankinen et al 2006). It is likely to assume that some variation in flower longevity found in T. polymorphum could be explained by this cause.…”

How does breeding system variation modulate sexual antagonism?

“…This, however, conflicts with the interests of any sperm or pollen donor, generating diverging selection on male and female traits that affect selfing (figure 2c). This idea clearly requires empirical attention, but previous work indicates that sexual conflict over post-pollination changes in stigma receptivity (Lankinen et al 2006;Lankinen & Kiboi 2007) and the degree of outcrossing (Luscher & Milinski 2003) may indeed occur.…”