Plants in the Central and South American genus Axinaea have a unique and highly complex bird pollination system, according to a new study published in the journal Current Biology.
This image shows a Sooty-capped bush tanager holding a stamen from Axinaea costaricensis in its beak. Note the pollen grains on the bird’s beak, front head, and cheeks. Image credit: Florian Etl.
Axinaea flowers offer up its male reproductive organs as a tempting and nutritious food source for the birds. As the birds seize those bulbous stamens with their beaks, they are blasted with pollen by the flowers’ complex ‘bellows’ organs. The birds then deliver that pollen to receptive female floral organs as they forage on.
“This unique and highly complex pollination system is completely new to science and provides another example of the intricate relationships that have evolved between flowers and their pollinators,” said Dr Agnes Dellinger from the University of Vienna, the first author on the study.
Axinaea flowers appear in clusters of a few to more than 20 flowers, with pink, red, yellow, or orange petals that usually don’t open completely. The stamens of those flowers stand out based on their contrasting colors and conspicuous, bulbous appendages.
Something else about the stamens also piqued curiosity of Dr Dellinger and her colleagues – one or more of these stamens was almost always found missing in the flowers they observed in the field or on herbarium specimens.
They learned what had happened to those stamens through a combination of pollination experiments, video monitoring, and detailed analyses of stamen structure and composition.
The scientists have observed multiple bird species, mostly tanagers, enjoying Axinaea food bodies and acting as pollinators in the process.
“The majority of bird-pollinated flowers offer nectar as a reward, and in the rare known cases involving food bodies, these reward tissues are restricted to the outer, sterile floral organs and are never found on reproductive organs,” Dr Dellinger said.
“Food bodies situated on male reproductive organs are otherwise only known from beetle-pollinated flowers. There is no other known example among plants of such a precise and anatomically distinct bellows organ.”
_____
Agnes S. Dellinger et al. 2014. A Specialized Bird Pollination System with a Bellows Mechanism for Pollen Transfer and Staminal Food Body Rewards. Current Biology, published online July 03, 2014; doi: 10.1016/j.cub.2014.05.056
