Biased Sex Allocation in Hermaphroditic Plants

Abstract

Female-biased sex allocation is commonly observed in hermaphroditic plants, though equal resource allocation to the female and the male functions is predicted to be evolutionarily stable in a simple model. I briefly reviewed factors that select for biased sex allocation in hermaphroditic plants; i .e., non-linear fitness, self-fertilization, non-linear trade-off in resource allocation to the female and the male functions, local mate competition, and pollen limitation. I also showed that the trade-off between growth and reproduction does not select for biased sex allocation unless constraints prevent simultaneous maximization of the amount of resources allocated to reproduction and equalizat i of resources allocated to the female and the male functions. Finally, I present a new hypothesis that can explain female-biased sex allocation. In this model, a source-sink relationship in flower/fruit growth was considered. The ESS sex allocation including fruits is femalebiased if fruit growth is sink-limited at least during its early stage.

Primary floral allocation per flower in 12 Pedicularis (Orobanchaceae) species: significant effect of two distinct rewarding types for pollinators

“…Variation in floral allocation per flower with respect to two rewarding types According to sex allocation theory (Charlesworth and Charlesworth 1981;Charnov 1982;Sakai 2000), for hermaphroditic plants, biased sex allocation should be determined by trade-off between male and female function gain in the condition of limited resources for obtaining maximized total fitness (Janzen 1977). For the nectarless rewarding plants in Pedicularis, its pollen may be major food resource of protein of bumblebee species (Goulson 1999;López et al 1999;Roulston and Cane 2000).…”

“…For cosexual plants, the pattern is considered to vary with environmental conditions and resources status (commonly associated with plant size), hence, induce to changed fitness contributions through these functions (Freeman et al 1981;Lloyd and Bawa 1984;Brunet 1992;Sakai 2000). Evidence of size or environment mediated sexual investment has been documented in numerous studies (de Jong and Klinkhamer1989; Klinkhamer et al 1997;Wright and Barrett 1999;Ashman et al 2001;Guitián et al 2003;Méndez and Traveset 2003;Guitián et al 2004;Zhao et al 2008).…”

Size‐dependent sex allocation in Aconitum gymnandrum (Ranunculaceae): physiological basis and effects of maternal family and environment

“…When female and male components of fitness are affected differentially by the amount of resources invested, then organisms are expected to modify their sex allocation according to their size (Ghiselin 1969; Charnov 1982; Lloyd & Bawa 1984; Iwasa 1991; Klinkhamer et al. 1997; Sakai 2000; Zhang & Jiang 2002; Sato 2004). Furthermore, without direct effects of size on fitness, theory suggests that when a male fitness gain curve decelerates more quickly (or accelerates more slowly) than a female curve, large plants are expected to emphasize female reproduction (de Jong & Klinkhamer 1989).…”

Plasticity in sex allocation in the plant Mercurialis annua is greater for hermaphrodites sampled from dimorphic than from monomorphic populations

“…Although the adaptive significance of this plastic variation is not always clear, evolutionary theory on size‐dependent sex allocation in hermaphrodites predicts shifts towards male or female function as plants grow in size as a function of the relative shapes of the male and female fitness gain curves (Zhang & Jiang, ). Plastic shifts in sex allocation in response to mate availability also make intuitive sense: plants should accentuate their male or female allocation with increased opportunities for mating as a male or a female, respectively (Sakai, ). The most striking example of this in plants is the development of the gametophytes of certain homosporous ferns as males or hermaphrodites depending on the density and gender of the immediate mating environment, with spores developing as males in the presence of hermaphrodites (and vice versa; Haig & Westoby, ; Banks, ; DeSoto et al ., ).…”