Ch. 23: Systematics, Phylogenies, and Comparative Biology -Systematics o Similar characteristics of all organisms One or more cells, metabolism, ATP, DNA o Diversity of life o Organisms grouped based on shared characteristics and molecular sequencing o Fossil records can’t provide al the informationo Systematics: reconstruction of evolutionary relationships o Phylogeny: hypothesis about patterns of relationship among specieso All species from one ancestor Descent with modification Phylogeny shows how recently species shared an ancestoro Similarity may not accurately predict relationships Rates of evolution vary and may not be unidirectional Evolution can be convergent -Cladistics o Derived characteristics: similarity inherited from most recent common ancestor o Ancestral similarity arose prior to common ancestoro Only shared derived characteristics are informative o Can be morphological, physiology, behavior, DNA o Characters should be recognizable o Ex of ancestral vs. derived Hair in mammals = derived Lungs in mammals is derived Shared derived feature of hair means mammals all share a common ancestor more recently than the common ancestor of amphibians and reptiles -Mutual Cladistics Analysis o First step: decide whether ancestral or derived use an out-group comparison out-group species don’t always exhibit ancestral condition if a state is exhibited by an outgroup, then it is ancestral -more reliable with more outgroups o Cladogram: depiction of hypothesis of evolutionary relationshipo Clade: species sharing a common ancestor as indicated by the possession of shared derived charactersEvolutionary units that show a common ancestor Synapomorphy: derived character shared by clade members Amniotes are clades for which evolution is a synapomorphy -Mammals are a clade and hair is a synapomorphyo Plesiomorphies: ancestral states o Symplesiomorphies: shared ancestral traits o Symplesiomorphies reflect character states inherited from different ancestors but don’t imply species are closely relatedo Homoplasy: shared character state that hasn’t been inherited from a common ancestor Convergent evolutionEvolutionary reversal o Systematist rely on parsimomy: favors the fewest assumptions o DNA sequencing reveals many characteristics o Character states are polarized by the sequence of an outgroupo Cladograms are constructed to minimize character evolution -Other Phylogenic Methods o Because of only four bases, high probability that two species will independently evolve the same character state o Statistical Approach Start with assumption about rate of evolution Fit data to derive best phylogeny o Molecular clock Rate of evolution is constant and divergence in DNA used to calculate times of branching -Systematics and Classification o Classification: how we place species into the taxonomic hierarchyo Monophyletic group: most recent common ancestor of the group and all its descendants o Paraphyletic group: most recent common ancestor but not all its descendants o Polyphyletic group: doesn’t include most recent common ancestor of all members of the groupo Taxonomic hierarchies are based on shared traits and evolutionary relationships -Species Concepts o Biological Species Concept: species are groups of interbreeding populations that are reproductively isolated o Phylogenetic Species Concept: species is a population set of characterized by one ore more shared derived characters o BSC can’t be applied to allopatric species because they can interbreed PSC takes into account if they are separated enough to develop derivedcharacterso BSC can only be applied to sexual species, while PSC can be applied to sexual and asexual o Critics of PSC says it leads to recognition of slightly different populations as separate species -Phylogenetics o Basis for all comparative biologyo homologous structures: same ancestral source o homoplastic structures: not derived from same ancestral source o phylogenetic analysis determines which is which-Comparative Biologyo Most complex characters don’t evolve in one step o Initial stages evolved as adaptation to some environmental pressureo Phylogenetic methods used to distinguish between competing hypotheses o Phylogenetics helps explain species diversification Use analysis to suggest and test hypotheses-Disease Evolutiono AIDS first recognized in 1980s but was around for more than a million years as SIV in primates o Phylogenetic analysis of HIV and SIV HIV descended from SIVDifferent strains of HIV exist -Independent transfers from primate species -Human strain is more closely related to a different strain of SIVthan other HIV strains Humans acquired HIV from different host species -Each subtype of HIV is most closely related to a different strainof chimp SIVo Chimps passed SIV to humans-Subtypes of HIV 2 are most closely related to west African monkeys, so they’re most rare -HIV mutates rapidly so one HIV infected individual can contain many different genotypes o Possible to create a phylogeny of strains and identify them to one