Asymmetry in wild mustard, Sinapis arvensis (Brassicaceae), in response to severe physiological stresses

It has often been assumed that when a severe stress is applied to a growing Organism asymmetry in a number of different traits will occur due to abnormal development. To test whether asymmetry is correlated with fitness in plants, and whether different environmental stresses cause distinct or similar forms of asymmetry, we measured fluctuating asymmetry in Sinapis arvensis (Brassicaceae),grown in several environments: five characterized by a distinctive environmental stress (high boron,high salt, low water, low light, low nutrients), and a 'control' environment that was as stress-free as possible with ample water, nutrients and light. Relative to the controls, all of the stress environments increased asymmetry and decreased fitness. Asymmetry fan be used to gauge environmental stress in S. arvensis, but the organ affected depends on the stress. For example, petal asymmetry was greatest in the high salt treatment, whereas fruit asymmetry was greatest in the low light treatment. Asymmetry also varied among traits within individuals; an individual's asymmetry rank depended on which organ was being examined.. Finally, individual fitness was not strongly correlated with asymmetry, indicating that asymmetry cannot be used to cull stress-intolerant individuals from a population during selection. Our results suggest that asymmetry may often be specific, and not general. Under a specific asymmetry model, a particular stress affects the development of a particular organ or set of organs, but not necessarily the whole plant.