l
Gender
bending in a Mexican forest
Plant
reproductive biology continues to provide fertile ground for good research.
Take, for example, the phenomenon of distyly in hermaphrodite plants, the
subject of the paper by González et al. (Veracruz, Mexico, pp.
371–378). In distylous plants, there are two floral morphs
that differ in respect of style length. The authors point out that in several
species this ensures outbreeding because fertilization can only occur between
the two different morphs. There are also species that, despite being
morphologically hermaphrodite, allocate resources to female function in one
morph and male function in the other, although complete ‘functional
dioeciousness’ is rare. The work described in this paper was focused on a distylous
hummingbird-pollinated shrub, Palicourea padifolia. It grows in Central
American cloud forests and, at least in the population under investigation, the
two morphs are equally represented. Allocations to male and female function
were studied in the same population over a 5-year period. In general, the
long-styled (LS) plants produced more flowers per inflorescence, perhaps
indicating a tendency to male function (more flowers being equated with greater
pollinator attraction and the possibility of greater donation of pollen). This
is consistent with the observation that hummingbirds transfer pollen from LS to
short-styled (SS) plants. However, pollen flow in the other direction does
occur (both morphs set fruit) and this may be mediated by insects. In terms of
female function, the data are variable. In two of the study years, SS plants
clearly invested more in female function than did LS plants. In two years there
was no difference and, in one of the study years, the LS plants were ‘more
female’ than the SS plants. Functional gender expression, as the authors term it, in wild populations of P. padifolia
thus varies from year to year, throwing doubt on previous single-year studies.
It will be interesting to know what causes this
variation.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
