Af. Rocheleau et G. Houle, Different cost of reproduction for the males and females of the rare dioecious shrub Corema conradii (Empetraceae), AM J BOTANY, 88(4), 2001, pp. 659-666
Males and females of dioecious plant species often differ in their reproduc
tive investment. Such differences frequently result in differential demogra
phic costs represented by lower growth, survival, and/or frequency of repro
duction, and/or by more Variable reproductive effort through time for femal
es. We present the results of a study on Corema conradii, a rare dioecious
shrub of the coastal dune heathlands of northeastern North America. We esti
mated the reproductive investment of both males and females, determined the
ir age structure, and compared their spatial patterns in a population at li
es-de-la-Madeleine, Quebec. We also determined the sex ratio of the foul po
pulations known to occur on the islands. Males invested more in reproductio
n at flowering. but when fruit production was considered, female reproducti
ve investment was higher in terms of biomass, Mg, and Ca, but not in terms
of N. P, and K. The age frequency distribution of males and females did not
differ significantly from one another. The population dispersion pattern w
as contagious. with patches of similar-age individuals. There was no spatia
l segregation between males and females, although the sex ratio varied some
what spatially. Females did not start reproducing at a later age than males
and did not appear to have a shorter longevity. However. the crown and rad
ial growth rates of females were lower than those of males. When estimated
by the crown intercept method, the sex ratio of all four populations was ma
le biased. However, because males had a higher crown growth rate, genet sex
ratio was in fact balanced. Higher investment in reproduction was associat
ed with a lower growth rate, which represents a differential cost of reprod
uction according to sex in this species.