Researchers from the Departments of Ecology and Genetics from the University of Granada have provided the first evidence of the help of natural selection in zygomorphy, which refers to flowers with only one plane of symmetry, in a natural population of Sierra Nevada. The researchers have noticed in the species studied, Erysimun mediohispanicum, that zygomorphic flowers are more frequently pollinated and show higher biological fitness, both because of the number of seeds produced and the number of seeds that germinate and survive to the juvenile phase. The research results have been recently published in The American Naturalist journal.
Charles Darwin proposed the fundamental evolutionary mechanism known as ‘natural selection’. This mechanism is based on the idea that the environmental conditions determine the effectiveness of certain special features in some organisms for survival and reproduction.
According to the researchers leading this research, José M. Gómez, Francisco Perfectti, and Juan Pedro M. Camacho, in the field of flora, flower-shape change has evolutionary meaning, because it is very important for the biological fitness of the plant. However, unlike other features such as the size, this morphology is a very complex concept, which is difficult to measure and therefore to assess. Because of this, the studies on the evolution of floral morphology are scarce and, in fact, “there is not much information about the adaptation capacity of flower-shape change under natural conditions”.
The scientists from Granada are pioneers in joining forces to study the morphological evolution of the species Erysimun mediohispanicum, which is characterized by the great intraspecific variety of its floral form.
To study flower-shape change, these scientists have applied a technique that is not very usual in these kinds of studies–geometric morphometry. This technique is a tool in which the shape changes can be studied with the movement of morphometric points, from a planar image of the flower (taken by a digital camera). The two-dimensional space relationship of these points is consistently maintained, so that the shape of the species studied can be reconstructed with the desired precision. The space changes can be appreciated thanks to this set of graphical and analytical methods.
The result of this process has been a variation pattern of everyone of the 300 specimens studied in a population in Sierra Nevada. Since the species studied blooms only once, the patterns found are for two years. They are, therefore, studies of microevolution in which subtle changes are observed through few generations.
Natural Selection in favour of zygomorphic flowers
The researchers have not only investigated flower morphology, but also have demonstrated that plants with zygomorphic flowers (flowers with only one plane of symmetry) are more frequently pollinated and they show higher biological fitness. For this reason, “natural selection favours zygomorphic flowers”. The researchers have presented “the first evidence of natural selection helping zygomorphy in a natural population”.
It is known (based on phylogenetic trees), that for millions of years, ancestral flowers were radial (they had two or more planes of symmetry), unlike modern ones that are bilaterally symmetric or zygomorphic. These variation patterns have enabled the researchers to trace the evolution from radial symmetry to zygomorphy in a process that has been called “microevolution of zygomorphy”. The microevolution has therefore been compared with macroevolution, which involves changes over a larger time scale.
Reference:
Prof. José M. Gómez Reyes. Dpto. de Biología Animal y Ecología (Animal Biology and Ecology) Universidad de Granada. Telephone Numbers: 958 248 915 – 958 248 590. E-mail. jmgreyes@ugr.es