1/17/2012 Class Aves Avian Systematics • Subclass Sauriurae • Systematics deals with evolutionary – Infraclass Archaeornithes - Archaeopteryx relationships among organisms. Allied – Infraclass Enantiornithes - Opposite birds with classification (or taxonomy). • Subclass Ornithurae • All birds are classified within the single – Infraclass Odontornithes - New World Class Aves toothed birds – 2 Subclasses – Infraclass Neornithes – 4 Infraclasses • Superorder Paleognathae - ratites and tinamous • Superorder Neognathae - all other birds Avian Systematics • Living birds comprise approximately: – 30 Orders – 193 Families – 2,099 Genera – 9,700 species Avian Phylogeny based on Feduccia (1995) 1 1/17/2012 Avian Systematics Avian Systematics • In practice, it can be difficult to delineate • Basic unit of classification = Species species from subspecies (geographical – Biological Species Concept = a species is variants) by both definitions of species. a group of similar looking individuals that are capable of interbreeding successfully • 2 Schools of Thought on differentiating – Molecular Species Concept = a species is species: a group of organisms that are diagnosably – Lumpers = tend to group similar forms into different genetically from other groups of a single species organisms – Splitters = tend to differentiate species when only minor variation present Avian Systematics Bases for Classification • The goal of systematics (and • Morphology = physical characteristics classification) is to provide a correct – historical method by which phylogenies phylogeny (evolutionary family tree) for derived organisms. – still a common method, particularly for • Avian systematics deals with how the fossil birds phylogeny of modern birds is • Biochemical Evidence = closely related established. birds should have more similar genes than more distantly related birds • Supplementary Evidence 2 1/17/2012 Morphology Morphology • Cladistics = a method of using a number of • Physical characteristics used for characters to establish a cladogram, which establishing phylogenies must be presumably outlines the evolutionary shared derived characters, rather than relationships among species based on these primitive characters. characters. • If two birds share a derived character, • Caution: a cladogram is only as good as the we can hypothesize that they shared a characters that are put into it, so careful choice must be used in entering characters common ancestor with that same into the model. derived character. Morphology • Morphological evidence alone is not sufficient to derive correct phylogenies. • One problem is convergent evolution = two species which are not closely related may look similar because they are adapted to similar lifestyles or environments. •Examples: – Auks (N hemisphere) vs. Penguins (S hemisphere) – New World Warblers and Australian Thornbills 3 1/17/2012 Penguins – southern Hemisphere Auks – northern Hemisphere New World Warblers Australian Warblers/Thornbills Biochemical Evidence Biochemical Evidence • Protein Electorphoresis = method of • DNA/DNA Hybridization = also an attempt to separating proteins in an electric field measure amount of genetic similarity. More depending on their charge, which reflects direct than using proteins. their amino acid sequence. – Fragments of single stranded DNA from 2 species • Ideally, this should measure the genetic associated under specific conditions. Forms 2- distance between 2 birds, because the amino stranded hybrid complex. acid sequence is dependent on the DNA – Hybrid complex then heated until dissociation. sequence. – Higher numbers of shared base pairs lead to increased thermal stability, so the more similar the • Not used much anymore. DNA, the higher the heat required for dissociation. 4 1/17/2012 Biochemical Evidence Biochemical Evidence • Problems with DNA/DNA Hybridization • DNA Sequencing = measures genetic – Differences may reflect adaptive radiation (and similarity of a portion of the genome (usually associated rapid DNA change) rather than distant certain specific genes) directly. ancestry • Measures nucleotide sequences of certain – Natural selection acts on phenotype not on genes directly (often use mitochondrial DNA) genotype (convergence is also possible within DNA) • Most direct measure of genetic similarity and – There is some argument over how accurately the common method for deriving phylogenies thermal stability reflects actual DNA sequences. currently. • DNA/DNA hybridization not used much • Usually will use several genes to verify anymore. phylogeny. Supplementary Evidence Supplementary Evidence • Behavior = related species should show • Karyotypes = shapes and numbers of similar unique (derived) behaviors chromosomes. Again, should be most similar – Example: New World Vultures historically between closely related species. assigned to Falconiformes based on morphology. • Ectoparasites = external parasites are often Share unique habit of urinating on legs to increase specific for a particular species of bird. heat loss when hot with storks (Ciconiiformes). DNA evidence supports relationship with storks. Closely related birds should have similar ectoparasites since they evolved along with • Biogeography = ranges of closely related the birds. forms should be geographically closer than more distantly related forms. • TAKE HOME = systematics is not a static science, but is dynamic, changing as new information comes to light. 5.