HANNAN, GARY L. Department of Biology, Eastern Michigan University, Ypsilanti, MI 48197. - Phenotypic gender modification in Platystemon californicus (Papaveraceae), a wind-pollinated, self-incompatible annual.
Current sex allocation theory assumes that a trade-off exists between
allocation to male versus female reproductive effort because a limited
pool of resources is available for reproduction. Expected fitness
gains derived from investment of resources in each sex differ among
pollination mechanisms, mating systems, and plant sizes (including
architecture). Platystemon californicus is a
self-incompatible, wind-pollinated annual plant exhibiting strict
modular growth and extreme variability in numbers of stamens, pollen
grains, carpels and ovules within flowers, providing an opportunity to
detect results of selection for shifts in phenotypic gender in plants
from diverse habitats, of different sizes and at different
developmental stages. Number of male and female reproductive
structures per flower exhibited significant variation among 41
populations. Comparisons of field versus garden-grown plants from
seven populations indicated that numbers of male and female structures
were mostly genetically based. Theory predicts that wind-pollinated
species should allocate an increased proportion of resources to male
function as plants become larger. I found that flowers of larger
plants had more stamens, carpels, and ovules and produced more pollen
than did flowers of smaller plants. However, the only difference in
relative allocation to male vs. female structures was for the ratio of
stamens to ovules per flower; larger plants had more stamens per
ovule than did smaller plants. Earliest flowers on a plant generally
had fewer stamens, carpels and ovules than did later flowers, but
relative numbers of flower parts did not differ significantly with
developmental stage (although trends toward increasing maleness were
found). Although P. californicus is extremely variable in
floral construction within and among populations and among plant size
categories within populations, the patterns of phenotypic gender
modification inferred by current theory were not found.
Key words: Papaveraceae, phenotypic gender, Platystemon californicus, sex allocation theory