First evidence of plants evolving weaponry to compete in the struggle for selection

Last updated: 29 May, 2014

Rutting stags and clawing bears are but two examples of male animals fighting over a mate, but research in New Phytologist has uncovered the first evidence of similar male struggles leading to the evolution of weaponry in plants.


The team, led by Dr. Andrea Cocucci from the Instituto Multidisciplinario de Biologia Vegetal of Argentina, studied a species of milkweed (Apocynaceae), found in tropical climates. While plants do not mate like animals, but rather reproduce via pollinators such as insects or birds, competition between individuals to exploit those pollinators can result in confrontation between the plants.


Milkweed reproduce by hooking sacs of pollen grains, known as pollinia, to the bodies of birds and other pollinators, which can be unwittingly dropped into another flower to complete pollination.


It is possible for multiple pollinarium to become entangled together due to the limited number of attachment points on the pollinator, and this Dr. Cocucci’s team believe, is the source of confrontation.


The team studied the South America milkweed genus Oxypetalum and found horn-like structures on the pollinia sacs which have no obvious biological use. The paper suggests that these horns are used to prevent the sacs from being hooked together with pollinia from other parent plants.


“Our results suggest that neither self-propulsion nor well-developed sensory perception are required for sexual selection to take place through intrasexual struggles,” said Dr. Cocucci. “Apparently, only physical contact is enough to influence the mating success of competitors and to promote the evolution of defensive and attack weaponry.”


An example of the horned pollinaria found in South American milkweed. (Photo Credit: Andrea Cocucci)

An example of the horned pollinaria found in South American milkweed. (Photo Credit: Andrea Cocucci)


The authors also produced a couple of nice video simulations of the pollination process showing the concatenation mechanism which can be downloaded from the article Supporting information on this page:


Original press release published by Wiley on March 20, 2014:


The article was also featured in the 29th March 2014 issue of The Economist: Locking horns: Sexual selection in plants.


A Commentary on the paper was published in issue 203:1 of New Phytologist: Peter CI, Shuttleworth A. 2014. Catching on to concatenation: evidence for pre-pollination intra-sexual selection in plants. New Phytologist 203: 4–6.



Cocucci AA, Marino S, Baranzelli M, Wiemer AP, Sérsic A. 2014. The buck in the milkweed: evidence of male–male interference among pollinaria on pollinators. New Phytologist 203: 280–286.