Radial and Bilateral Fluctuating Asymmetry of Iris pumila Flowers as Indicators of Environmental Stress

Abstract

In this study we compared the biomonitoring potential of various types of flower asymmetry indices in Iris pumila (Dwarf Bearded Iris). We chose 197 naturally growing clones from the arid steppe habitat in the largest sandy area in Europe (Deliblato Sands Nature Reserve), and we transplanted two replicates of each clone to a polluted highway site with a heavy traffic flow. After a period of acclimatization, lower levels of photosynthetic pigment concentrations and higher stomatal density and specific leaf area in transplants verified that the chosen highway site was indeed more stressful and therefore suitable for estimation of the flower asymmetry biomonitoring potential. We analyzed radially and bilaterally symmetrical flower structures (radial fluctuating asymmetry (RA) and bilateral fluctuating asymmetry (FA)) on three perianth parts—falls, standards, and styles—and calculated various asymmetry indices based on linear and geometric morphometrics. Despite utilizing a heavily polluted environment and fairly large sample sizes, only one asymmetry index was significantly higher on the polluted site with demonstrated stressful effects on utilized plants, indicating that flower asymmetry was not an efficient method for biomonitoring in the case of I. pumila RA and FA indices.

Phenotypic Selection on Flower Traits in Food-Deceptive Plant Iris pumila L.: The Role of Pollinators

“…In I. pumila, the shape and symmetry of the individual floral organs do not seem to play an important role in attracting pollinators, since no difference between the shapes of pollinated and non-pollinated floral organs was observed for both the symmetric and asymmetric components of shape variation. In the previous studies on I. pumila, FA has been used as a tool to evaluate developmental instability in response to environmental and pollution stresses [56,57]. The underlying hypothesis was that a more stressful environment would be reflected by a higher floral organ shape FA [26,28,56,57].…”

“…In the previous studies on I. pumila, FA has been used as a tool to evaluate developmental instability in response to environmental and pollution stresses [56,57]. The underlying hypothesis was that a more stressful environment would be reflected by a higher floral organ shape FA [26,28,56,57]. In addition, symmetric structures are thought to be a pollinator's innate preference [23].…”

Male sterility significantly elevates shape variation and fluctuating asymmetry of zygomorphic corolla in gynodioecious Glechoma hederacea (Lamiaceae)

“…However, it should be noticed that published evidence for the relationship between the FA of flower parts and fitness-related characteristics of plants is not unambiguous, and several studies did not find any such relationship in various plant species ( Waldmann 2001 ; Siikamäki et al 2002 ; Barišić Klisarić et al 2016 ). Likewise, Barišić Klisarić et al (2019) reported only a weak relationship between the pollution from highway traffic and shape FA in flowers of Iris pumila .…”