Sex Ratio Variation in the Dioecious Shrub Oemleria cerasiformis

Abstract

Many examples of biased sex ratios are known in natural populations of plants. Proximal causes of these biases are gender diphasy (sex changing), differential mortality between male and female genets, differential rates of clonal growth (numbers of ramets per genet), and differential flowering (differences in flowering frequency or age to maturity). In the western North American shrub Oemleria cerasiformis we determined sex ratios for 60 natural populations and found an excess of males in 56 populations. The male bias was greatest in populations with little recent recruitment. Sampling of young and old plants indicated that males flowered at an earlier age than females, which led to a transient flowering bias in very young plants, and that the genet sex ratio was 1:1 in young mature plants but male biased in old plants, as a result of differential mortality. Examination of dead genets confirmed that mature females have higher mortality rates. Females also have greater reproductive effort and slower growth rates than males. The major cause of biased sex ratios in O. cerasiformis is greater mortality of female plants during their reproductive years, which probably arises directly or indirectly from their greater allocation to reproduction.

Sex-specific pattern of spatial genetic structure in dioecious and clonal tree species, Populus alba L.

“…Sexdependent pattern in clonal plants has been revealed also for mortality (Allen and Antos 1993) and reproductive success (Matsuo et al 2014). No doubt all of these life-history traits may have an impact on population dynamics and demography which are closely related with fine-scale SGS.…”

“…It is widely assumed that females incur higher costs of reproduction owing to flowering and fruiting processes (Lloyd and Webb 1977;Obeso 2002;Vessella et al 2015). Consequently, this may lead to resource allocation trade-offs affecting female survival rates (Obeso 2002), growth (Iszkuło and Boratyński 2011;, clonal growth (Allen and Antos 1993) or other fitness-related traits, which in turn may give rise to sexrelated demographic patterns.…”

“…Ramet-level male-biased sex ratio is frequently reported among clonal species and is ascribed to more intensive clonal reproduction of males (Allen and Antos 1993;Matsushita and Tomaru 2012;Petzold et al 2013;Yakimowski and Barrett 2014). Male-biased sex ratios either at the ramet or genet level are commonly attributed also to higher mortality in females, which is linked to their higher resource demands (Lloyd and Webb 1977;Obeso 2002) leading to resource allocation trade-offs affecting survival rates (Allen and Antos 1993;Petzold et al 2013). None of these was monitored by us in field as the single-season study design precludes tracing the dynamics of the ramet production or mortality which requires long-term observation, especially in long-living tree species.…”

Biomass allocation patterns and allometric relationships between components of the androdioecious Acer tegmentosum

“…The theory of plant life history is largely concerned with optimal resource allocation between male and female functions (Allen and Antos 1993;Rocheleau and Houle 2001). It is assumed that there is a resource tradeoff between reproductive and vegetative distribution (Popp and Reinartz 1988;Allen and Antos 1993;Antos and Allen 1999;Obeso 2002;Torimaru and Tomaru 2012).…”

“…It is assumed that there is a resource tradeoff between reproductive and vegetative distribution (Popp and Reinartz 1988;Allen and Antos 1993;Antos and Allen 1999;Obeso 2002;Torimaru and Tomaru 2012). A number of comparative studies have examined sexual dimorphism, although some disagreement persists with this issue.…”