Abstract
Most dioecious plants are trees. However, because of the difficulty in
determining sex from vegetative morphology, previous investigations of
the sex ratios of dioecious trees were limited to flowering individuals,
leading to inadequate and potentially unreliable data on patterns of sex
ratios and the underlying mechanisms driving their variation. Here, we
applied sex-specific molecular markers to investigate the sex ratio of a
fully mapped population of the dioecious tree Diospyros
morrisiana (Ebenaceae) in a subtropical forest. We also investigated
the sexual dimorphism of life-history traits and spatial association
between male and female trees to determine potential processes shaping
the sex ratio at different life stages. Molecular sexing revealed a
female-biased population sex ratio for this D. morrisianapopulation, contrasting with the male-biased operational (i.e.,
flowering) sex ratio. The sex ratio of D. morrisiana shifted from
female-biased to male-biased over older life stages. We found that
reproduction had a larger impact on the growth of female trees, which
may account for the ontogenetic shift in sex ratio. There was no
evidence of spatial segregation of the sexes beyond a scale of 2
m. Through molecular sexing of
all individuals across all life stages, our work revealed for the first
time a shift from a female- to a male-biased sex ratio in a huge
population of a dioecious tree species. To better understand variation
in sex ratios and the underlying mechanisms in dioecious trees, the sex
of non-flowering and juvenile individuals should be included in future
studies.