Geopolitics in a buttercup

It is difficult to explain how mutualisms evolve and then persist in the face of selection for cheating behavior. A classic example of a mutualism is that between globeflowers Trollius europaeus and their specialist and obligate pollinating flies. Because the fly larvae eat globeflower seeds, the host plants effectively ‘pay babies to get babies’. In a new paper, Ferdy et al. use an adaptive dynamics model to show how globeflower morphology can so intensify fly larval kin competition that female flies are selected to lay small clutches of eggs, even at the cost of having to visit more flowers. Fewer eggs result in fewer seeds being eaten and, therefore, floral morphology alone could result in the evolution and maintenance of this mutualism.