Flowers change scent to advertise different rewards
The secret is in the floral scent
Male and female flowers advertise different "rewards" by giving off different scents, scientists have said.
Mated female epicephala moths prefer the smell of male
flowers, suggesting male flower scent triggers pollen collecting
behaviour.
The female moths then transfer the pollen from male flowers to the female flowers in which they lay their eggs.
The team analysed the scent from both male and female flowers and found major differences in their chemical make-up.
According to the researchers, this is the first example where
male and female floral scent is used to signal the alternative rewards
provided by each sex of flower to their pollinators.
The results are published in the journal Proceedings of the Royal Society B.
Physical and behavioural differences between the sexes
(sexual dimorphism) is widespread in the animal kingdom, for example
antlers on male red deer and the ornate plumage of some male birds.
It is much less common in plants
with separate male and female flowers, because the same pollinator needs
to visit both sexes to ensure fertilisation.
But in some members of the phyllanthaceae, a family of plants
found in the tropics and sub-tropics, there is a unique bond with
epicephala moths where single sex flowers offer different rewards.
"The female moth is attracted to male flowers to collect
pollen before depositing it in the female flower ensuring pollination
for the plant, and by laying her eggs here she secures the seeds as food
for her young," explained lead researcher Dr Tomoko Okamoto from Kyoto
University, Japan.
In the dark these moths use only scent signals from the
flowers to find host plants, with each moth species only pollinating one
species of plant.
"Epicephala moths have an excellent ability to handle
olfactory information which other insects do not have, supporting the
highly specific interaction and complicated behaviours," said Dr
Okamoto.
So the team collected floral scents from epicephala moth
pollinated and non-epicephala pollinated flowers and analysed them using
a technique called gas chromatography-mass spectrometry (GC-MS).
This allowed them to "visualise the differences in the scent samples," according to Dr Okamoto.
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- Growing in the tropics there are about 2000 species in the phyllanthaceae family.
- Epicephala moth pollinated plants have both male and female flowers on the same individual (monoecious).
And what they found were dramatic
differences in the scent profiles between male and female flowers in
moth pollinated plants, but no differences between the sexes in non-moth
pollinated plants.
"The volatile compounds emitted by male and female flowers
are very different, often involving compounds derived from different
biosynthetic pathways," Dr Okamoto told BBC Nature.
While behavioural tests with mated female moths that had no
experience of pollen were shown to prefer male floral scent over the
female one.
"[This is] the first example in which sexually dimorphic
floral scent has evolved to signal an alternative reward provided by
each sex," said Dr Okamoto.
The team also suggest that plants pollinated by epicephala moths evolved this trait independently.
Dr Okamoto explained: "[These] moths have a very high ability
to handle the olfactory information which triggers the complicated
behaviour.
"Very small insects have a big world."