The phylogenetic relationship of birds of prey
Prof. Dr. Michael Wink is coordinating the "Molecular Evolution" research project at the University of Heidelberg, which deals with topics such as evolutionary research, biodiversity and systematics as well as molecular ecology. Modern DNA analysis methods have shed new light on the relationships between birds of prey.
The creation of new genealogical trees in the field of molecular evolution is based on the comparison of DNA sequences. Selected marker genes of the species of interest – these might be protein-coding genes or rRNA genes – are compared and their homologies assessed. It is also possible to determine molecular differences using DNA fragment length analyses of PCR-amplified repetitive DNA stretches. These repetitive sequences originate from small genome segments of which the vertebrate genome possesses between 20,000 and 30,000. The analysis focuses on several loci of what is known as microsatellites (STR) or minisatellites (VNTR). In order to be able to analyse a large number of loci in a short period of time, several loci are simultaneously amplified using a method known as multiplex PCR.
The molecular clock
Due to the mutations accumulating in these DNA stretches (mainly through deamination, depurination or dimerisation), the species-specific sequence differences become greater the longer two species have been separated from each other. This molecular clock enables the fairly accurate reconstruction of the relationships between species and genera and evolutionary processes, because they are not derived from phenotypical or morphological traits. This information is worth keeping in mind, because cladistics (=method of biological systematics) only groups monophyletic groups that are derived from a common ancestor into taxonomic units such as genera or families. Not all current taxonomic groups fulfil this criterion as it is often the case that convergent or less informative morphological traits lead scientists to draw false conclusions about the evolution of the organisms being compared.
Monophyletic and convergent
Professor Wink used comprehensive DNA analyses to investigate the evolution of birds. He was able to show that the evolution of the birds of prey, which exist in many different regions of the world, and that of vultures is not the same as is claimed by current systematics.
Based on nucleotide sequence data of the mitochondrial cytochrome b gene and the nuclear gene RAG1 (recombination gene in T cells), Prof. Wink’s team was able to show for 300 birds of prey and owl taxa whether the Falconiformes/Strigiformes orders and the individual families represented monophyletic groups or whether the morphological adaptations of birds of prey and vultures – such as strong, hook-shaped beaks, strong feet with claws, excellent vision and excellent flying capacity – did not develop independently from the different relationship circles. The scientists were able to show that the falcon, hawk, osprey and owl families formed monophyletic groups, which are however not closely related to each other. Falcons and owls form independent groups with no close relationship to the true birds of prey. Similarities in their lifestyles can most likely be ascribed to convergence, i.e. to an independent development of certain traits due to the same selection pressure. Inheritance did not affect the development of these traits.
The convergent evolution of birds of prey can be best explained using vultures as an example. Sequence analyses confirmed that New World vultures (e.g. Andean condor – Vultur gryphus) are not related to Old World vultures (e.g. Griffon vulture – Gyps fulvus), but belong to the taxonomic group of Ciconiidae (storks and similar birds). However, this does not mean that they are part of the stork family. New World vultures have a common ancestor with petrels, cranes, flamingos and stork and are hence regarded as a monophyletic group in the order of Ciconiiformes. The researchers’ results also suggest two lineages among the Old World vultures: Bearded vultures, Egyptian vultures and Palmnut vultures most likely represent a very old evolutionary lineage, which also includes honey buzzards, which are no close relatives of the true buzzards (e.g. common buzzard – Buteo buteo). Griffon vultures (see above) and cinereous vultures represent a second, independent evolutionary lineage.
In another project, Wink and his colleagues reconstructed the speciation of singing birds (robins, kinglets, blue tits) on the Canary Islands on the basis of the nucleotide sequences of the mitochondrial cytochrome b gene. Volcanic islands, the age of which can be determined with reasonable accuracy (Canary Island cytochrome b is assumed to be between 1 and 20 million years old), are regarded as excellent models of allopatric speciation (this means that the populations evolve in geographic isolation). It appears that the Canary Islands were colonised in several events by birds from the European or African mainland. The DNA sequences enable the differentiation of distinct island populations, of which some have to be regarded as new subspecies or even species.
DNA analyses as a tool for the protection of species
The example of Manx Shearwater (Puffinus puffinus) seabirds living in Mediterranean regions shows the practical use of these new findings in the systematics of birds. DNA analyses identified the two subspecies P. p. velkouan and P. p. mauretanikus as two distinct species, which led the protective status of the birds to be raised from Birdlife International’s SPEC category 4 to SPEC category 2.
Thus, molecular evolutionary research is also able to make a concrete contribution to the increased protection of a particular animal species – which is in keeping with the noble goal of sustainably maintaining and protecting biodiversity.
About Professor Wink
Prof. Dr. Michael Wink studied biology and chemistry at the University of Bonn. After his PhD, he habilitated in pharmaceutical biology at the Technical University in Braunschweig in 1984. Supported by a Heisenberg grant of the DFG, he then worked at the MPI for Breeding Research and the Gene Centre at the LMU in Munich. In 1988, he was appointed professor at the University of Mainz and one year later became professor of pharmaceutical biology at the University of Heidelberg, where he heads the Department of Biology at the Institute of Pharmacy and Molecular Biotechnology (IPMB). Wink has authored more than 460 peer-reviewed papers and numerous reference and textbooks.
© BIOPRO Baden-Württemberg GmbH
Selected literature: Volker Storch, Ulrich Welsch, Michael Wink: Evolutionsbiologie, 2. edition, Springer Publishing House, Berlin Heidelberg 2007