Arisaema
triphyllum, jack-in-the-pulpit, is a perennial herb that lives
in the understory of eastern deciduous forests. Its ability to change
sex has fascinated biologists for years. In their first few years
of life, A. triphyllum do not flower at all. Later, when they
are larger, plants produce male flowers. When plants reach a large
size, they are able to produce female flowers. Because jack-in-the-pulpits
have no woody parts, they are capable of shrinking from one year to
the next; when they do, they usually change from femaleback to male.
Thus, small jack-in-the-pulpits are male, large ones are female. Individuals
make this switch many times in their 20+ year lifetimes.
I discovered that this reproductive strategy is a way for plants to
increase their lifetime fitness (i.e. overall number of offspring).
Jack-in-the-pulpit seeds are large and require considerable energy
to produce; by contrast, pollen is much less expensive. By reproducing
as males when they are small, individuals act as fathers, shifting
the energetic cost of reproducing to those individuals that serve
as their offsprings' mothers. Without this option, individuals in
poor condition (because of herbivory, drought, or a heavy reproductive
year) would have to forgo reproduction for a year or more.
