Did Drosera evolve long scapes to stop their pollinators from being eaten?
OBJECTIVE
Insectivorous plants frequently display their flowers on the ends of long racemes. Conventional wisdom is that long racemes in insectivorous plants have evolved to provide spatial separation between flowers and traps, which consequently prevents pollinators from being captured. However, it is also possible that long racemes evolved for better seed dispersal or to make flowers more visible to pollinators.


METHODS
Two sympatric insectivorous plants with identical pollinators were studied: Drosera cistiflora, with an upright growth form but a short raceme; and Drosera pauciflora, with a basal rosette of traps and a very long raceme. If long racemes evolved to protect their pollinators then D. cistiflora should capture more pollinators than D. pauciflora. However, if long racemes evolved to attract pollinators then taller flowers should receive more pollination visits than shorter flowers.


RESULTS
Examination of D. pauciflora and D. cistiflora traps revealed that no pollinators were captured by either species, suggesting that long racemes did not evolve to protect pollinators from being captured. Experimental manipulations of flower height in D. cistiflora showed that experimentally shortened plants received significantly fewer pollination visits than plants which were taller in stature.


CONCLUSIONS
Long scapes in Drosera and non-insectivorous plants probably evolved due to similar selective pressures such as pollinator attraction.
Anderson
Bruce
B
Department of Botany and Zoology, University of Stellenbosch, Matieland 7602, South Africa. banderso.bruce@gmail.com
D000818:Animals; D005075:Biological Evolution; D029787:Drosera / Q000033:anatomy & histology* / Q000502:physiology*; D035264:Flowers / Q000033:anatomy & histology* / Q000502:physiology*; D054817:Pollination / Q000502:physiology*