Credit: N. MUCHHALA & J. D. THOMSON

Proc. R. Soc. B doi:10.1098/rspb.2009.0102 (2009)

Darwin suggested that particularly long-tongued pollinators and long-tubed flowers are dancers in a sort of coevolutionary tango, each acting as selection pressure on the other. When faced with a flower that keeps its nectar at the end of a long tube, a nectar bat (Anoura fistulata, pictured) with a longer-than-average tongue has an advantage over its shorter-tongued conspecifics. Now, Nathan Muchhala and James Thomson of the University of Toronto, Canada, have shown that pressures run the other way as well.

The duo experimentally manipulated the length of the flower Centropogon nigricans and found that longer tubes delivered more pollen to bats in male flowers, and took more pollen from bats in female flowers. The exact mechanism, however, remains unknown.