The bull in the milkweed: evidence of animal-like male-male competition in plants.

COCUCCI A. A.; MARINO, S.; BARANZELLI, M.; WIEMER, A. P.; SÉRSIC, A. N.

Mainz

Simposio; 21st International Symposium of the German Botanical Society; 2012

Sexual selection was originally defined for animals as dependence of the mating success on competition between conspecifics over mates through physical or sensory interaction. Secondary sexual characters (SSC) were recognized as the evolutionary outcome of this kind of selection, with direct physical interaction leading to differences in fitness. Pollinaria of milkweeds may physically compete for access to attachment points on the pollinators? body, and occasionally pollinaria may link onto pre-existing pollinaria on a pollinator resulting in concatenation. We tested the hypotheses that concatenation may result in interference between proximal and distal pollinaria and that features of non- concatenating pollinaria might be attributed to prevention of concatenation, by analyzing pollen donation efficiency, experimental manipulation of the phenotype, and the phylogenetic patterns of co-occurrence of traits. It is shown that concatenation was able to diminish the reproductive performance of proximal pollinaria, that horns on pollinaria prevented concatenation, and horn acquisition was correlated with a loss of concatenation. The experimental removal of horns in species that did not concatenate reverted to concatenation. The present evidence appears to be the first of male body-body struggles in the fashion that is known in animals, and this may represent the first ever recognized SSC in plants.