Canopy seed storage is associated with sexual dimorphism in the woody dioecious genus Leucadendron

Abstract

Summary1. Species of the dioecious South African plant genus Leucadendron vary strikingly in their degree of sexual dimorphism, with males of dimorphic species typically possessing more and thinner branches and smaller leaves than the corresponding females. 2. Many Leucadendron species are serotinous, with females of serotinous species maintaining seeds in transpiring cones for a number of years. Since cones must be kept alive, serotinous females presumably incur higher costs in terms of water loss than non-serotinous females and, particularly, males. Given that branching architecture is known to affect water conductance, with less resistance in less highly branched plants, we predicted a positive correlation between the degree of serotiny in a species and sexual dimorphism in branching. 3. We tested the effect of serotiny and several other factors on the degree of sexual dimorphism in Leucadendron by conducting a comparative analysis of variation across 49 species using phylogenetic regression. 4. There was a strong positive association between the degree of serotiny and sexual dimorphism. This association is consistent with the idea that the costs of maintaining cones may select females to be less highly branched than males. 5. Synthesis. Serotiny is a strategy of maternal care that contributes to offspring survival after seed maturation. We found that, in Leucadendron, the evolution of increased serotiny corresponds with the evolution of more marked sexual dimorphism. This study exposes a hitherto unidentified association between sexual dimorphism and maternal care in plants and points to a possible additional reproductive burden carried by serotinous plants compared with those that release their seeds at maturity.

Ecological genetics of sex ratios in plant populations

“…Samples of female, male and non-reproductive plants exhibit male-biased sex ratios in four younger populations, but close to even sex ratios in older populations in which all individuals were reproductively mature (figure 2). This pattern is most probably explained by the longer time required for females to reach reproductive maturity because of costs associated with serotinous cone production (see Harris & Pannell 2010), and assumes that non-flowering individuals in the younger populations examined are largely female. Populations of most dioecious species are composed of mixed age cohorts and it is therefore more difficult to assess the influence of age on sex ratio dynamics.…”

The role of breeding system in community dynamics: Growth and mortality in forests of different successional stages

“…A study analyzing the sex ratios of 126 dioecious species has showed nearly continuous variation from strong male to strong female bias, and exhibit male‐biased sex ratios in some younger populations, but close to even sex ratios in older populations in which all individuals were reproductively primary (Barrett, Yakimowski, Field, & Pickup, 2010). In an ultimate manner, the changing sex ratio was attributed to the longer time required for females to reach reproductive maturity because of costs associated with serotinous cone production (Harris & Pannell, 2010), in which significant resource is also invested.…”

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

“…Not surprisingly, this result accords with the predictions that there are clear tradeoffs between vegetative and reproductive matters. Harris and Pannell (2010) reported that females of highly serotinous species were less branched than males in dioecious Leucadendron. Another study showed more branches and smaller leaves in males than in females (Midgley 2010).…”