Evolution boffins buzzing over bee discovery

By Dave Chambers

Scientists have discovered why a South African bee species grew extraordinarily long legs.

Research at Stellenbosch University has found that oil-collecting Rediviva bees‚ first described in 1984‚ evolved legs of up to 23mm to harvest oil from the equally long spurs of snapdragon flowers.

The females from this species of oil-collecting bees in South Africa (Rediviva longimanus) have disproportionately long legs with dense hairs on the feet. They use the front legs to collect oil from the equally long spurs of the snapdragon flower (Diascia whiteheadii). Picture ANTON PAUW

“This is one of the few examples where a pollinator had to adapt to the flowers that it pollinates‚ rather than the other way round‚” evolutionary ecologist Anton Pauw wrote in the peer-reviewed Proceedings of the Royal Society B: Biology.

Lead author Pauw‚ from Stellenbosch’s botany and zoology department‚ said flowers often adapted to their pollinators in spectacular ways in order to be able to reproduce.

In this case‚ however‚ Rediviva bees had developed front legs of varying lengths —up to 23.4mm in the case of the “longimanus” variant — to reach oil produced at the back of the snapdragon’s twin spurs.

Spur length also varies between the 70 species in the largest genus of oil-producing flowers (Diascia)‚ which is also indigenous to South Africa.

A snapdragon flower (Diascia whiteheadii) with an open flower and several buds. The twin spurs contain oil. Picture ANTON PAUW

The bees’ front legs are coated in dense velvety hairs that soak up the oil‚ which is then mixed with pollen to form a super-nutritious bread for larvae in underground nests. The oil is also used to line nest walls.

Working with researchers from Germany‚ the UK‚ Belgium and the US‚ Pauw analysed DNA to produce a family tree for 19 of the 26 Rediviva species.

“We were able to show that very closely related bee species often differ dramatically in leg length and that this divergence could be explained by differences in the spur length of the flowers that they visit‚” he said.

Documenting interactions between oil-collecting bees and the 96 plant species they visit required years of observation. Many of the oil-secreting plants flower only the first year after a fire.

Pauw said the next step would be to analyse snapdragons’ genes to test whether spur length and leg length evolved simultaneously. “Oil-collecting bees are threatened by man’s activities‚ in particular by urbanisation. By understanding their role in generating and maintaining plant diversity‚ it might be possible to predict and ameliorate human impacts‚” he said.

-TMG Digital


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