Just like men and women have different preferences and tastes in sights and smells, so the sexes of the bee fly can be fickle – especially when it comes to the looks of the daisy they prefer to visit. Unlike humans, though, female bee flies tend to opt for the more boring option.
This is the finding of researchers of the Department of Botany and Zoology at Stellenbosch University, who are studying the interaction between pollinators and plants in the Cape flora. Mr Marinus de Jager, a doctoral student in botany, and his supervisor Dr Allan Ellis, have published a study on gender-specific pollinator preferences for floral traits in the international journal Functional Ecology.
The beetle daisy (Gorteria diffusa) commonly grows along road verges and in the most arid veld types from the south of Namibia, to Namaqualand and the Little Karoo. Remarkably, one finds fourteen different floral forms or “types” of this one species of daisy. In previous studies, at least thirteen of these different floral forms have been counted within a 300 km range in Namaqualand, with another being found in the Little Karoo only. They vary in colour from bright orange to light yellow. Most of these flower forms also have insect-like black spots on them.
The bee fly (Megapalpus capensis) is the most common pollinator of the beetle daisy (Gorteria diffusa).
In 2010, Dr Ellis and fellow researcher Prof Dr Steven Johnson of the University of KwaZulu-Natal (UKZN) showed how the daisy deceives male bee flies into visiting it, all in an effort to spread their pollen effectively.
“The special markings or ornaments on their petals closely resemble female insects and so attract amorous, pollinating males,” Dr Ellis sums up the findings of previous studies. “This type of sexual deception was previously thought only to have been mastered by orchids.”
In the latest study, the Stellenbosch University researchers found that the bee fly shows strong gender-specific interactions with the variety of insect-like spots which characterize the beetle daisy.
Male and female flies exhibit contrasting preferences for spot components, the research shows. Females prefer simplistic spots and avoid any spots with ultraviolet (UV) highlights.
Males, on the other hand, have less boring preferences and tend to visit daisies with three-dimensional raised spots and glossy spots. Males also prefer spots with tiny white UV reflecting highlights on them.
“If you have a close look under a UV light, you will see that female flies also have UV highlights on their bodies,” reports Mr de Jager. “This is probably why male flies prefer to visit this type of spot, because they actually think it’s a female fly.”
In line with women’s so-called sense for the more refined things in life, such as perfume, the female bee flies preferred to visit flower spots with a floral odour, while males were not fussy about smells.
“This means that in contrast with orchids, sexual deception in the beetle daisy is achieved largely by the flower’s ability to visually mimic a female insect, all in an effort to lure male pollinators,” says Mr de Jager.
Their findings add to the research team’s understanding of why one finds so many flower forms of the beetle daisy in nature. It seems to boil down to this annual flower spreading its risks to attract potential pollinators to its flowers, all in an effort to ensure that the necessary seed bank is available for the next year’s flower season.
“Our results clearly show that these elaborate insect-like spots have evolved in response to male preferences,” says Dr Ellis.
“The trade-off that exists between attracting male and female flies may also have contributed to the different floral forms that one finds among beetle daisies in various regions,” Mr de Jager adds.
• This release is based on the article “Gender-specific pollinator preferences for floral traits” in Functional Ecology
Engela Duvenage, Media: Faculty of Science, Stellenbosch University
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