Fluctuating asymmetry and Echinospartum horridum fitness components

Abstract

In the last two decades, fluctuating asymmetry (FA) has been used commonly as an indicator of the stress experienced by individual organisms during development, although the technique has not been without controversy. In general, estimates of FA in populations have been positively correlated with measures of stress but, in the few studies in which it has been investigated, the correlations between estimates of FA and stress in individuals have been inconsistent. This study compared the FA in the opposite spines of stems and flowers to other bio-indicators of physiological stress in plants, such as annual crown growth ratio, annual flower production, annual crown death ratio, and branch fractal dimension. The position of an individual Echinospartum horridum within a patch influenced the stress conditions, and influenced its colonization strategy. Plants in the interior of patches are under high intraspecific competition due to negative density feedback (low flower production and branch biomass, and high annual crown death ratio), showed larger flower FA and spines FA repeatability (within-individual variation in FA) than plants at the periphery. Plant growth rates and the FA of spines were negatively correlated, but flower asymmetry and flower production was not significantly correlated, which reflects the capacity of E. horridum to adjust flower production to its developing conditions. We concluded that because organisms respond differently to different conditions, enhanced by the plasticity of plants in the development of morphological structures in response to changes in the environment, it is advisable to use multiple parameters to assess physiological stress in plants.