Pollination: with small rewards come bad results

Published in the journal Current Biology, this study will be mentioned during the SOL 2012 -- Solanaceae conference, taking place from August 26 to 30 at the University of Neuchâtel.

Nectar plays a central role in most plant-pollinator relationships. It serves as a reward for services rendered by visitors that transport the plant's pollen. In nature, certain orchid species do not honour this tacit agreement. Instead, the plant economises these energy resources which it might be able to relocate to other plant structures for its own advantage: vigorous growth, greater seed production or improve on its pest defence mechanisms.

However, can this pollination with a reduced reward work for cultivated plants in terms of increased yield? Anna Brandenburg decided to test this hypothesis on petunia, an ideal model plant for garden vegetables since it belongs to the same family as the potato or tomato, the Solanaceae family.

After performing multiple crosses for this research, the biologist was able to create petunia lines that produced a volume of nectar three times less than that of the standard Petunia axillaris. At first glance, it seems that the plant comes out ahead, since Anna Brandenburg observed that manual pollination resulted in an increased seed production (20% to 30% more) in the low nectar plants compared to P. axillaris.

However, everything changes once the natural pollinators come into play. The hawkmoth (Manduca sexta) clearly spends less time visiting flowers offering a smaller reward, which consequently results in a considerable reduction in seed production. Thus, a simple self-serving action of the hawkmoth, namely the reduction of drinking time per flower, is sufficient to prevent the spread of cheating Petunias.

This situation, however, is reversible. By adding nectar to the flower varieties that produce less nectar, Anna Brandenburg was able to attract the pollinators' attention. Hence, with the hawkmoth staying longer on the plant, the quantity of seeds produced corresponds to the one that the biologist obtained with manual pollination.