Single sex flowers differ by scent

A female epicephala moth pollinating a phyllanthaceae female flowerThe 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.

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Battle of the sexes

A peacock

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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Glochidion lanceolatum

  • 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.”

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