Male plants of the species Leucadendron xanthoconus (left) turn yellow near blooms, out-showing females of the species
(right). Like male animals trading practicality for sex appeal, the display may hinder survival but boost mating.
sowed pollen from one clone or from
two in little growth cups furnished with
identical nutrients that substituted for
female tissue. Because no actual female
tissue was around to influence growth,
variation among males reflected just the
interactions of the males.
In some combinations, pollen from
different trees germinated much as it
did when set out alone. But other combinations seemed to pit pollen grain
against pollen grain. Most dramatically,
a particular northern clone’s germination rate ended up dropping 46 percentage points when the clone was paired
with a southerner than when it was left
to germinate alone.
Pine pollen grains travel by air instead
of by insect, and a lucky pollen bit lands
in a droplet of liquid exuded by the
female organ. Once in the droplets, pollen grains release proteins in the course
of absorbing moisture and preparing to
fertilize the ovules. Perhaps, Varis speculates, some of these compounds might
start molecular fights. Even if a female
just accepts whatever pollen succeeds
in reaching the right places, males may
influence their mating success by sabotaging each other.
Male flowers of broadleaf arrowhead, a
North American aquatic plant, appear to
compete by showing off instead of sabo-
taging. The insect-pollinated Sagittaria
latifolia separates its sex organs in dif-
ferent flowers, although sometimes the
same individual plant grows both male
and female flowers. In a survey of all
variations, individual male flowers grow
bigger than female ones, Barrett and
two Toronto colleagues reported in the
September Annals of Botany. Research-
ers looking at all the male flowers on a
particular plant, single-sex as well as
hermaphrodites, found that the male
displays lasted longer than female dis-
plays, with new flowers opening as old
ones finished blooming.
s J.C. Moore and J.R. Pannell. “Sexual
selection in plants.” Current Biology.
March 8, 2011.