What makes the sex ratio female‐biased in the dioecious tree Salix sachalinensis?

Abstract

Summary1. The female-biased sex ratio in the genus Salix is widely documented, but little is known about the ecological mechanisms causing this bias. We investigated the flowering sex ratio, population dynamics, clonality and spatial segregation of the sexes in three Salix sachalinensis populations of different ages (young, intermediate and old) for a total of 2922 trees over 3 years. 2. Spatial segregation of the sexes did not occur in any of the populations. 3. Flowering sex ratios were female biased (2 : 1) in both the intermediate and old populations, but were slightly male biased in the young population. The female-biased sex ratios in the mature populations were due to the increasing number of flowering females with increasing plant size, but not to differences in demographic parameters; neither mortality nor growth rate differed between the sexes in any population. 4. Amplified fragment length polymorphism analysis revealed that there were very few clonal individuals in any population, suggesting little effect of clonality on the biased sex ratios. 5. These results suggest an initially and inherently determined female-biased sex ratio in mature S. sachalinensis populations.

The influence of hydrological regimes on sex ratios and spatial segregation of the sexes in two dioecious riparian shrub species in northern Sweden

“…Females have been found on more nutrient-rich sites than males (Bierzychudek and Eckhart 1988) and on sites with lower soil temperatures (Dawson and Bliss 1989). Other studies do not find SSS, for example Gamache and Houle (1997) studying S. planifolia in sub-arctic Canada and Ueno et al (2007) studying S. sachalinensis in northern Japan. Where SSS is not evident, it is suggested by Dudley (2006) that it may be taking place through different niche properties than those measured, for example, the less visible and less easily measured use of rooting spaces.…”

“…Yet other studies report 1:1 sex ratios in all environments for some species, for example, Kaul and Kaul (1984) for P. deltoides Bartr. It is possible that where there is no bias in the sex ratio, males and females of a species might respond to prevailing environmental conditions by differential production of pollen and ovules (Niesenbaum 1992) or changing flowering sex ratios (Ueno et al 2007). …”

“…Marshall (Nichols-Orians et al 1993); an inherent, genetically based imbalance in sex ratios Ueno et al 2007) and density-dependent controls (Falinski 1980). Seed sex ratios in dioecious species may play an important role in resulting sex ratios among adult plants ( de Jong et al 2002), but in many members of the Salicaceae it is not possible to know the seed sex as reliable molecular markers linked to sex determination genes have not been easy to identify (Alström-Rapaport et al 1998;Semerikov et al 2003).…”

“…Much of the research conducted on northern and alpine willow species has found female-dominated sex ratios, e.g. S. arctica -2:1 (Dawson and Bliss 1989), S. rosmarinifolia L. -3:1, S. aurita L. -4:1, S. caprea L. -2:1 (Falinski 1980), S. sachalinensis -2:1 (Ueno, Suyama and Seiwa 2007). Attributing this biased sex ratio to SSS is difficult because a range of factors may be involved including: differential mortality through preferential vole feeding on males in S. myrsinifolia Salisb.−phylicifolia L. (Danell et al 1985;Elmqvist et al 1988) though this has not been found in S. polaris Wahl.…”

Female versus male: Rumex thyrsiflorus Fingerh. under in vitro conditions. Does sex influence in vitro morphogenesis?

“…Early maturation of male individuals is common in dioecious plants, probably because of their lower costs of reproduction compared to females (Obeso 2002;Ueno et al 2006). As a result of earlier reproduction of males, there could be a higher number of males in young populations (Ueno et al 2007 and references therein). In most cases, the data on sex ratios focuses on flowering plants, because it is difficult to evaluate the sex of non-reproductive individuals without genetic sex markers, and one cannot exclude the sex-related differences in seed viability (Stehlik and Barrett 2005;Pickup and Barrett 2013).…”