PHYLOGENY and SYSTEMATICS CHAPTER 25

VOCABULARY Phylogeny – evolutionary history of a species or related species Systematics – study of biological diversity in an evolutionary context

CLASSIFICATION Kingdom Phylum Class Order Family Genus Species

Figure 25.7 Hierarchical classification

Figure 25.8 The connection between classification and phylogeny

Built from shared derived characters Homology – shared likeness due to common ancestry ( YES!) Analogy – shared likeness due to convergent evolution ( NO!) Convergent evolution – species from different evolutionary branches may come to resemble each other due to similar ecological roles and natural selection How is a phylogeny built?

Figure Parsimony and the analogy-versus-homology pitfall

Figure Convergent evolution and analogous structures The ocotillo of southwestern N. America (left) looks like Alluaudia of Madagascar (right).

EVOLUTIONARY HISTORY OF TAXA Monophyletic – when a single common ancestor gave rise to all species within that taxon (ideal) Polyphyletic – members of a taxon are derived from 2 or more common ancestors Paraphyletic – when a taxon excludes species that share a common ancestor

Figure 25.9 Monophyletic versus paraphyletic and polyphyletic groups

MOLECULAR BIOLOGY AND SYSTEMATICS Species diverge only when changes occur in nucleotide sequences Species that are phylogenetically closely related have more similar nucleotide sequences

Protein comparisons Problem- Does not use all DNA of organism DNA/RNA comparisons DNA hybridization – compares H bonding Restriction maps using restriction enzymes (often with mtDNA) DNA sequencing Using PCR to clone trace amounts of DNA RNA sequencing Changes slower than other DNA What do we use to construct phylogenies?

PHYLOGENETIC SYSTEMATICS Phenetics – based on measurable similarities and makes no phylogenetic assumptions Cladistics – classifies according to the order in time that branches arose along a dichotomous tree Clade – an evolutionary branch Outgroup – a species that is relatively closely related to the group of species being studied, but is clearly not as closely related as any study group members are to each other

Synapomorphies – shared derived characteristics Characteristics that are homologous and evolved in an ancestor that is common to all species on one branch of a fork, but not common to other branch Parsimony – find the simplest explanation

Figure Constructing a cladogram

Figure Cladistics and taxonomy

Figure Modern systematics is shaking some phylogenetic trees (this means class Reptilia in its traditional form is paraphyletic, not monophyletic)