Pollen Performance and Sex‐ratio Evolution in a Dioecious Plant

Abstract

Abstract.-There has been a proliferation of studies, in a variety of taxa, that have detected sex-linked or cytoplasmic genes that enhance their own transmission via sex-ratio distortion. One of the most important parameters influencing the dynamics of these elements is the magnitude of their transmission advantage. In many systems, the mechanism of sex-ratio distortion is to abort X-or Y-bearing gametes. With this mechanism, the transmission advantage associated with sex-ratio distortion is diminished when the production of male gametes limits offspring production or when competition among the gametes of different males is intense. In this study, we analyzed the outcome of pollen competition between males that produced different sex ratios in the dioecious plant, Silene alba, and estimated how the sex-ratio bias influenced the transmission properties of the sex chromosomes. We varied the intensity of pollen competition by controlling the quantity of pollen used in crosses and used a combination of single-male pollinations and pollen mixtures to evaluate the effects of multiple paternity. Paternity in pollen mixtures was estimated using allozymes. Sex-ratio bias was directly influenced by the quantity of pollen, but the magnitude of this effect was small. The relative performance of pollen from different males varied substantially, especially when there was multiple paternity. Specifically, males with biased sex ratios sired far fewer offspring of either sex in pollen mixtures. In crosses involving single males, however, these "sex-ratio" males produced the same number of offspring as other males, so the female bias caused a significant transmission advantage for X-linked genes. X-linked genes could enhance their transmission via sex-ratio distortion in Silene populations, but the magnitude of this transmission advantage will depend on the ecological circumstances that influence the opportunity for multiple paternity.

The influence of demography and local mating environment on sex ratios in a wind‐pollinated dioecious plant

“…Our results on the influence of population size, plant density, and the composition of the local mating neighborhood in R. hastatulus highlight the interaction of ecology, demography, and genetics for sex-ratio variation. Although the importance of certation has been controversial (Carroll and Mulcahy 1993;Taylor et al 1999), our study provides further evidence in support of the hypothesis that this mechanism contributes toward female-biased sex ratios.…”

Does Landscape Fragmentation Influence Sex Ratio of Dioecious Plants? A Case Study of Pistacia chinensis in the Thousand-Island Lake Region of China

“…High quantity pollen (pollen mixture from several males) could produce more female progeny than low quantity pollen (pollen from a single male) [16]. Similar results were also found in the dioecious herb Rumex nivalis, where stronger female-biased sex ratio progeny were presented with maternal parents closer to the males due to the pollen tube competition [17].…”

“…Sex-biased herbivory might also create a biased sex ratio [13], [14], [15]. Other studies of progeny sex ratios have observed that pollen competition might produce different sex ratios in offspring [16]. High stigmatic pollen loads can induce pollen tube competition and produce stronger female-biased seed sex ratios [17].…”

Pollination Intensity Influences Sex Ratios in Dioecious Rumex Nivalis, a Wind-Pollinated Plant

“…Although primary sex ratios in S. latifolia are often female biased, the degree of bias is far less pronounced in comparison with Rumex (Carroll and Mulcahy 1993;Taylor 1994). In controlled crosses males produce heritable differences in sex ratios ranging from slightly male biased to strongly female biased (Taylor 1994(Taylor , 1999Taylor et al 1999;Ingvarsson and Taylor 2002). This heritable variation is unlikely to be subject to environmental modification in a manner similar to the way that pollination conditions alter sex ratios in Rumex.…”

“…Meiotic drive or segregation distortion can result in the selective abortion of male-determining gametes resulting in a bias in the frequency of female-determining gametes (Taylor and Ingvarsson 2003). Segregation distortion has been detected in Silene latifolia (Taylor 1994(Taylor , 1999Taylor et al 1999;Ingvarsson and Taylor 2002), the other well-studied dioecious species with heteromorphic sex chromosomes (Charlesworth 2002). Although primary sex ratios in S. latifolia are often female biased, the degree of bias is far less pronounced in comparison with Rumex (Carroll and Mulcahy 1993;Taylor 1994).…”