Translational and Fluctuating Asymmetry as Tools to Detect Stress in Stress-adapted and Nonadapted Plants

Plants having experienced previous exposure to a stress are expected to be more resistant to further stress than those not having been exposed. While the assessment of stress in plants is a difficult task, particularly for stress-adapted plants, developmental instability has proven a useful tool for assessing stress in organisms. We examined the effect of water availability on developmental instability (translational asymmetry and fluctuating asymmetry) and growth of Anthyllis cytisoides L. under a precipitation gradient. We compared A. cytisoides in very xeric (Almerı́a, 256 mm of average rainfall) and subhumid (Málaga, 613 mm of average rainfall) areas, from northand south-facing slopes, after both a period of extreme drought (1995) and a humid period (1997). Translational symmetry varied between northand south-exposed plants but differently for the Almerı́a and Málaga populations. We observed that developmental stability was enhanced in southexposed plants in the population from the more xeric habitat (Almerı́a) after both dry and humid periods. In contrast, A. cytisoides living in a subhumid habitat did not alter their developmental stability in response to exposure after a humid period but exhibited a decline in stability in south-exposed slopes after a dry period. That is interpreted as a consequence of the adaptation of A. cytisoides to aridity. Growth patterns were also investigated. By reducing growth, plants can mitigate stress through a reduction of water and nutrient demands, allowing the maintenance of a steady supply of nutrients for developmental stability. This strategy was followed by plants acclimated to drought. But in mild weather, such as that of Montes de Málaga, a high growth rate cannot be supported when water is scarce. We also observed that floral fluctuating asymmetry was greatest on north-facing slopes at both the Almerı́a and Málaga sites. That is, southern exposure enhanced floral homeostasis during development. Additionally, comparisons between translational and fluctuating asymmetry showed that translational asymmetry is more sensitive to environmental change than fluctuating asymmetry.